US2326724A - Roofing - Google Patents

Description

Au'g- 10, 1943 G. A. FAsoLD Ef A1. y 2,326,724

ROFING Filed June 20, 1941 3 Sheets-Sheet l ATTORNEYS Aug. 10, 1 943. G. A. FASQLD ET AL ROOFING Filed June 20, 1941 3 Sheets-Sheet 2 Aug.` 10, 1943;.` v G. A. FAsoLD ET AL ROOFING Filed June 20, 1941 5 Sheets-Sheet 3 INVENTORS www@ @ma BY W' ATTORNEYS Patented Aeg. 1o, 194.3

' Rooms George Arthur Fasold, Mount Healthy, lanni Harold W. Greider, Wyoming, Ohio, assignors to The Philip' Carey Manufacturing Company, a. corporation of lOhio Application June 20, 1941., Serial N0. 399,024

Claims.

This invention relates to roofing and the manufacture thereof an-dis a continuation in part of our applicationSerial No. 347,154 filed July 24, 1940. This invention relates particularly to roofing embodying bituminous material as a Waterproofing. While reference is made to roofing, this term is used generally as referring to waterand weather-resistant coverings such as shingles (individual or strip shingles), roll roong, cap sheets, sidings, roof deck coverings made from such preformed materials, built up roofings and the like. l

Heretofore bituminous prepared roof-lng has been very extensively manufactured using as a base a fibrous web such as a sheet of roofing felt, impregnating the fibrous web with a bituminous material, and coating one or both surfaces of the impregnated web with a weather-resistant bituminous coating material. The bituminous coating material usually contains a mineral filler such as slate flour or powdered limestone. Usually there is applied to the bituminous coating on the surface intended to -be exposed to the weather a suitable granular material such aS slate granules or iinely divided mineral surfacing material such as talc or mica. Finely divided materials suchas mica flakes, talc, 'silica dust or the like may be made adherent to the non-weather exposed surface of the roofing to prevent sticking of the adjacent layers of the roofing material in the package.

According to the present invention rcoflngs. for example rooflngs of the character referred to. can .be improved to a very pronounced degree as will appear more in 'detail hereinbelow. An im-` blistering resistance -but also is greatly improved in fire resistance, and the manufacture of roofings having both high blister resistance and high fire resistance is also an important feature and objectof this invention. While improvement in re resistance is not a necessary incident to all embodiments of this invention, those embodil- `ments .which have improved re resistance are regarded as preferred embodiments of the present invention. The importance of high iire re sistance is self-evident. According to the present invention a `roofing of the relatively inexpensive -bituminzed felt type can be made which is comparable in fire resistance to more costly nonbituminous types of roofing such as slate and asbestos cement shingles. In our pending application Serial No. 370,638 led December 18,'1940. for Roofing and material for rooting and the manufacture thereof,.we have described roongs and roof coverings which are primarily characterized by their high nre resistance 'and which include embodiments that do not necessarily have lthe high blister resistance of the present invention. This application in certain respects like- Wise is a continuation in part of said application Serial No. 370,636.

It is another important aspect of this invention that the blister prevention and also fire re- V sistance can be obtained without sacrifice of other desirable attributes of the roofing and thatv in preferred embodiments of this invention the roong can be improved in respects other than blister resistance and fire resistance. Thus, roofings, having a bituminized fibrous web base and that embody this invention Ihave been made which exhibit greatly improved strength in comparlson with rooflngs of this type heretofore made as measured by such well known tests as the Mullen bursting test and the tensile strength test. Moreover, roongs embodying this invention, e. g., in the form of shingles, can be made .which are considerably tougher and more resisty ant to impact shocks than ordinary rooiings heretofore made and which likewise have greater physical stability under conditions of exposure to weather, are less subject to deteriorative changes, and have improved resistance to sliding. It is a further advantageof this invention that rooflngs may be made which have improved temperature susceptibility, that is, which exhibit less changejn properties with temperature changes than do ordinary bituminized roongs heretofore made. According to preferred embodiments of this invention, roofings are afforded which, While somewhat stiffer than ordinary bituminous roofings heretofore made at normal atmospheric and at roof temperatures, are more pliable and ilexible Without rupture at lower temperatures such as 50 F. and even at 32 F. Moderate stiffness at ordinary atmospheric temperatures and at roof temperatures is a desirablel quality, but excessive brittleness and lack of pliability either `at normal atmospheric temperatures or at low temperatures such as occur when a roofing becomes hard and brittle upon prolonged ageingr are objectionable.

According to this invention the blistering problem is-remedied by providing a bituminous layl' or coating for the roofing which is of such stront nature at summer sun roof surface temperature as to successfully resist the formation of blisters due to the vapor pressure of entrapped moisture at such temperature/s and which at the same time has the other qualities and characteristics that are desirable in a bituminous roong and even improves upon such other qualities and properties, e. g., in the respects mentioned above. This tuminous roofings which carry a coating of asphalt that especially under summer sun temper- -atures is highly plastic and is readily deformed and blistered by any moisture that becomes entrapped in void spaces of the roofing.

Heretofore blistering has for many years been a serious defect of bituminous rooflngs and numerous attempts have been made by technologists in the industry to remedy blistering. So far as we are aware the rooflngs that have been made heretofore which afford the highest resistance to blistering are roofings that have been manufactured utilizing the method and apparatus which we have disclosed in our United States Patents Nos. 2,105,531 and 2,159,587, the improved product of high resistance to blistering and high durability being covered by our Patent No. 2,159,586, and roongs embodying the inventions of these patents have been manufactured and sold in very large quantities. In these prior patents we have pointed out how the porosity of a bituminous roong and particularly the porosity of a base sheet such as roofing felt, can be reduced to an exceedingly small percentage thereby minimizing the blistering tendency. While the present invention may be utilized in conjunction with the inventions covered by our aforesaid patents and in preferred practice is so used, this is not necessarily the case inasmuch as exceedingly high resistance to blistering can be afforded by different means, namely, by providing a coating which is so strong at summer sun roof surface temperatures that it acts as a blister barrier through which blisters cannot push from beneath and in which blisters cannot form and Without utilizing the inventions of our prior patents.

In those embodiments of this invention which have high fire resistance, the fire resistance is due to the composition and characteristics of the bituminous coating composition or waterproofing layer. While the base sheet for the roofing might be made of non-combustible material this does not solve the problem if the bituminous Waterproofing coating itself burns or tends to spread the flame. One of the attributes of the coating composition which render it re resistant is that the coating while comprising an essentially thermoplastic bituminous base also comprises a nely` divided heat resistant material having surface characteristics such that as incorporated in the bituminous coating it is now resistant when the bitumen in the coating becomes softened by heating to elevated temperatures at or approaching flame temperatures and provides a skeletal mat which remains coherent and persists in place so that the `finely divided heat resistant material does not tend excessively to nov down an inclined roof deck, e. g., a roof deck having a 30 assenza '..sult in a coherent mat-'like mass which has high represents a radical departure from ordinary biheat insulating, properties and in preferred embodiments develops pores therein, augmenting the heat insulating effectiveness thereof so as to shield an underlying combustible roof deck from the heat of the flame. Another attribute of the fire resistant coating is that it is highly resistant to combustion so that any charring upon exposure to flame is gradual and discontinues without substantial spreading as soon as exposure to flame is discontinued and preferably the coating when subjected to llame temperatures is substantially non-bleeding, that is, the bitumen does not tend to separate and flow from the skeletal mat of heat resistant material but chars'and carbonizes whileremaining in place commingled with the finely divided heat resistant material.

Other features of this invention relate to the disposition of the special coating material in strata in roof deck coverings and to the disposition, character and quantity of the finely divided mineral filler in the coating material and in the roofing structure.

In order to afford a better understanding of the practice of this invention it will be described in connection with a specific example of the practice thereof which is both blister resistant and re resistant. The material that is used for the blister barrier and fire resistant surface coating or layer will rst be described. A typical bituminous base for this material is obtained by airblowing a residual asphalt flux from the refining of Mid-Continent petroleum to a softening point, ring-and-ball method, of about 220 to 240 F. The asphalt is heated to a heat-liquefied condition, and into the heated asphalt is incorporated. v about 40% of asbestos dust.

(The percentage being by weight based on the total weight of the mixed asphalt and finely divided asbestos.)

The nely divided asbestos in the form of asbestos dust is a by-product of the chrysotile asbestos milling industry and is characterized byv The bituminous mass containing the Afinely divided asbestos even at high mixing temperatures (about 400 to 500 F.) exhibits a certain physical stability and resistance to ow and exhibits senilplastic characteristics asdistinguished from being a highly iuid mass. Notwithstanding this semi-plastic state we have 'found that the mass can readily lbe applied to a suitable foundation by a coating operation. At temperatures of about 390 to 500 F. the high viscosity massapplies easily and bonds well to the base. At temperatures below about 390 F. the mass becomes somewhat difcult to work and does not spread as satisfactorily.

The base material that is used according to the present example of the practice of this invention is ordinary roofing felt made of vegetable and animal nbre, e. g., roofing felt weighing about 8 pounds per square feet. The felt is impregnated with a suitable bituminous impregnating material, e. g., a conventional bituminous roofing saturant having a softening point of about F. t about 160 F. 'Ihe roofing felt may beimcoated with the special coating composition using' -pregnated with the bituminous saturant and agitator in the reservoir for the mixed coating composition can be used for this purpose. We

have found that the mixing of the asbestos dust any conventional type of impregnating and coatexposed to fire is consumed quite readily.

Preferably, and for the purpose of the present example, the method andv apparatus disclosed in Our'Patents Nos. 2,105,531 and 2,159,587 are employed for the purpose of impregnating the vfeltl base in order to obtain maximum blister resistance and durability as well as maximum fire resistance. In so doing the felt is rst thoroughly impregnated with bituminous saturant as by passing it a plurality of times'through a bath of the saturant that is maintained at a temperature of about 350 to 400 F. After the felt is thoroughly impregnated with the saturant it is immersed in a bath of special bituminouscoating composition above described, maintained at a temperature of about 450 to 500 F. and, as disclosed in our aforesaid prior patents, is squeezed between squeeze rolls to expel residual airand vapors and is caused to become sealed with the a surface layer of the coating composition` that is substantially uniformly distributed and weighs about 50 pounds per 100 square feet of the roofing. The iineness of subdivision of the asbestos dust in the coating composition enables the composition to be spread to uniform thickness and with uniformity of distribution of the asbestos with the bitumen can be facilitated by preheating'it to at least about 390 F. before it is mixed with the bitumen. Preferably the nely-divided asbestos is heated to a temperature above the temperature at which the heat liquiiicd bitumen is maintained so that during mixing the bitumen is brought up to a desirably high mixing temperature due to the heat of the illler. For example,

we 'nave lfound it to be desirable to maintain bitumen in storage at about 400 F, and to preheat the finely-divided asbestos to about 500 F. When the bitumen is takenfrom the reservoir tothe mixer it is mixed with the asbestos du'st rwhich raises the temperature of the mixture to mediately prior to the coating step. By following the preferred procedure the bitumen can be handled and mixed without local overheating and the stiifening effect of the finely-divided asbestos interferes to a mininium extent with the mixing operation. Moreover, this procedure facilitates the application of the coating composition in a very uniform layer on the felt and in .a condition such that the finely-divided matedust in the coating. As the roong cools conventional mineral surfacing material such as slate granules can be applied to the surface forweather exposure and the granules can be partially embedded in the coating composition. The granular surfacing material is preferably substantially non-porous and is preferably substantially noncombustible. On the opposite side of the sheet there may be applied a thin coating of bituminous coating material, e. g., having a softening point of about 220 F. to 240 Ffso as to weigh about 5 pounds' per 100 square feet and a finely divided duhg material such as talc or mica dust or similab material may be applied and partially embedded in the coating. Preferably for maximum fire resistancev the back coating should be special coating composition embodying our invention, e. g., the same as applied to the top or weather y side of the sheet. Because of the relatively high temperatures employed in applying the coating material it is desirable to provide somewhat 'more cooling means than are customarily employed for cooling the roong so that the machine may be operated at normal speed and so that the finished roong will emerge at a temperature which is not excessively high and at which cutting and packing in the regular way are permitted.

In the special coating as applied it is important that the asbestos dust be disposed uniformly and continuously both in amountanddistribution over the base sheet. To this end the special 'coating material should be thoroughly mixed and should be applied in a thoroughly' mixed condition to the base sheet. A suitable rial will become distributed continuously and uniformly both in amount and distribution` over the felt. The foregoing 'preferred procedure is likewise preferable when finely-divided mineral fillers other than asbestos dust are used in the coating composition;

'Ihe roofing` as thus prepared Weighs about 105 pounds perv 100 square feet of sheet area. Of this Weight about 25% is in the form of slate granules adherent to one side and finely-divided dusting material adherent to the other side and the balance of the weight is the felt, the bituminous impregnating material and the special coating material. Because of the employment of the method and apparatus of our vPatents Nos. 2,105,531 and 2,159,587 the roofing as a' whole contained less than about '.5% of voids and the coating composition was sealedto the sides of the devoided felt and was integrally bonded with the bituminous saturant in the felt and with the fibers adjacent the surface of the felt and filled the surface interstices of the felt to substantial depth without substantial porosity. Moreover, the asbestos dust was keyed into the surface interstices of the felt and anchored thereto as a mat and the amount was reduced of 4asphalt in the special coating composition that might bleed The roofing as thus prepared exhibited many remarkable properties, a highly important property being its exceedingly great resistance to blistering. Blistering of an asphalt roofing is a defect which may appear very soon after application to the roof or it may develop gradually rwith increase in the number and size of the ings for blistering tendency various accelerated blistering tests have been devised bybituminous vvto the surface and tend to promote combustion.

reeling technologists which give a fairly accurate indication of blistering tendency. These methods have included (a) soaking the roongspecimen in water at ordinary temperature or' at an elevatedtemperature such as 125 F. to 140 F. followed by heating in an oven at a still higher temperature such as 175 F. or 220 F.; (b) heating the specimen in an oven to expel air, immersing it in water, and heating it again in an oven; ic) exposure of the specimen to repeated accelerated weathering cycles of exposure to actinic light, heat, wetting and drying, intense water spray and freezing, as in a Weather-Ometer; and (d) soaking a plurality of test specimens in water for varying periods of time followed by heating at 220 F., the minimum soaking time required to induce blistering being recorded.

The roong prepared as above described has been subjected to the foregoing tests, but we have found that these tests are not sufficiently severe to show the very great improvement in blister resistance of the' new product as compared with asphalt roofings made according to prior art practice. We therefore have devised a blister resistance test that is still more severe, and which consists simply in immersing roofing specimens in boiling water and noting the time that the specimens may be immersed without blistering. The drastic nature of this test is apparent When it is considered that commercial asphalt prepared roongs produced by ten of the largest manufacturers thereof blistered badly after only 30 to 60 minutes immersion in boiling water and several blistered badlyl after immersion of merely 15 minutes. By contrast, the roofing made as above described could be immersed in boiling water up to 'eight hours and even longer and remain virtually blister-free. This makes it apparent that according to the present invention roofing can be manufactured which exhibits a very remarkable improvement in blister resist-` The boiling water test is indicative of the capacity of the surface coating or layer as a whole to resist without blistering the vapor pressure at boiling temperatures of any air and moisture that may be entrapped `on or in a fibrous backing sheet and that tends to push out through the bituminous coating. The test is also indicative of the capacity of the surface coating or layer to resist absorption of water or moisture by the coating itself and penetration of water or moisture into the coating for, if the coating were to absorb substantial quantities of water or moisture, the absorbed water or moisture would form blister sources intermediate the thickness of the coating. We have found that to afford blister resistance to the highest degree, the blister barrier layer or coating should be of such high vvsicosity and strength as to resist without substantial deformation vapor pressure generated at summer sun roof surface temperatures of moisture entrapped underneath the layer or coating and the layer or lcoating should also be substantially non-water absorptive and sealed on the interior from access of Water.

At summer sun roof surface temperatures, any moist air entrapped in the roofing develops adenite vapor pressure in excess of atmospheric pressure unless'the pressure is relieved by escape of moisture vapor or by evaporation. Summer sun roof deck temperatures vary according to localities depending upon the climate, although in the mid-summer months roof surface temperatures in all parts of the United States are well above in the United States that tend to cause blistering occur in the centralgulf coastal area where there is high humidity combined with high roof temperatures which frequently attain F. although they seldom exceed F. In a few instances, roof surface temperatures as high as F. have been'recorded.

At temperatures such as 170 F., any moisture entrapped in void spaces of the roofing tends to expand due to vapor pressure developed therein, the maximum theoretical pressure that may be developed at 170 F. being, we have computed, about 41% greater than normal atmospheric pressure. At lower temperatures, e. g., at 160 F., the pressure differential is less and has been computed to be about 32% greater than normal atmospheric pressure. Bituminous coating materials which have been used heretofore generally have had a softening point of about 210 to 235 F. in commercial practice. Such coating materials become greatly softened or even semi-duid at summer sun roof surface temperatures such as 170F, and oer no substantial resistance to ployed is usually of a somewhat lower softening point than 210 to 235 F. so as to compensate for any effect the filler may have of raising the softening point of bitumen and so that the softening point of the bituminous mixture will still be about 220 to 240 F. and spreadable at about 300 to 375 F. In this case also, bad blistering may occur if any moisture becomes entrapped in the roofing. Moreover, when fillers have been used heretofore the fillers have not been of a suitable character to inhibit the effect of the filler of absorbing water into the coating and thereby causing blistering in the coating or layer itself.

When reference is made herein to a bituminous material vor coating or layer, reference is made to a material or coating or layer comprising bitu- .tar and the like which have not been mixed with filler material.

The blister barrier coating or layer of roofing embodying this invention does not become Weak and fluid at summer sun temperatures as is the case with ordinary bituminous roong coatings, but, due to its greatly reduced thermoplasticity, remains suliciently strong and highly viscous at such temperatures so as to enable it to resist the vapor pressure generated by entrapped moisture when subjected to summer sun roof surface temperatures and at such temperatures does not become deformed or stretched so as to result in blister formation. It is this property of the coating or layer that is regarded as being chiefly instrumental in affording the high blister resistance of roongs embodying this invention.

For bituminous roong embodying this inventon which is coated with a bituminous coating for weather exposure so that the coating weighs about 10 to 25 pounds per 100 square feet, it is .desirable that the` viscosity of the coating be at b sold in all parts of the United States it is preferable that the coating be of the high viscosity mentioned. The-viscosity of the roofing decomposition as against the water at 185 F. if the scribed in the-foregoing example. is considerably higher thanv` 4x10 poises, namely, -about 265x107 poises at 170 F. and is well able to withstand extremelyjsevere conditions of summer sun heat and moisture without blistering. For withstanding extremely severe conditions a viscosity of at least about 20X 10'I poises vat 170 F. is preferred, although, in the practice ofthis invention, the special composition can be made so as to have a considerably higher viscosity than 20x10'I paises at 170 F. The method used by' us in determining the viscosity of the coating material Was a modification of the alternating stress method described by R. A. Traxler and H. E. Schweyer in'A. S. T. M.- Proceedings, vol. 36 (1936), pages 518-529, the viscosity value being calculated from the rst displacement of ythe bituminous specimen in theextrusion tube.

Another factor in connection with the coating above described that is material in imparting remarkably high blister resistance, is that the. coating itself is substantially non-water absorptive..

Thus the coating is adapted for direct weather exposure as the surface is so impervious to water that the interior or body portion of the coating is substantially sealed from penetration of moisture. For this reason, the coating does not become weakenedV by ,absorbed moisture so as to lessen the capacity of the filler to reinforce the coating and so as to create blisterV sources intermediate the thickness of the coating, particularly about the filler particles. Asbestos dust or other finely-divided short chrysolite asbestos is especially desirable for use as a filler for blending with bitun minous coating material to reinforce and increase the viscosity thereof according to this invention because of its high and preferential afiinity for bitumen rather than for water even at high ternperatures and its capacity to afford a substantially non-water absorptive coating or layer.

A convenient test which we have devised for ascertaining whether or not a coating composition is adequately non-water absorptive and resistant to moisture, is to apply the coating com-` position to a non-porous base sheet such as metal, e. g., aluminum, and then immerse the sheet with the coating adherent thereto in water at about 185 F. If the coating composition when applied in a layer substantially .020 inch in thickness lto the non-porous sheet can be immersed in the water at 185 F. for'about 10 hours or longer without exhibiting small blisters or pockmarks, the coating composition is very highly resistant to water at such temperature and is regarded as non-water absorptive as this term is used herein. Coating compositions having such high resistance to water at 185 F. can readily be made according to this invention and are preferred. If the coating composition under the described test conditions is resistant to water at 185. F. for about 2 hours or more without exhibiting small blisters or pockmarks, the coating material still has very markedly improved resistance to water at 185 F. as compared with coating compositions for rooiings heretofore made. When it is said herein that the material of a coating composition is resistant to water at 185 F., it is to be understood thatl resistance to water under the described test conditions is intended. Moreover, if the coating composition contains a filler, this same test is indicativeof whether or not the filler has a preferential affinity yfor water as compared with its afiinity for the bitumen in the composition, and the fill/elvis to be regarded as having a preferential affinity for bitumen in the bituminous coating composition in question is capable under the described test conditions of remaining substantially free of blistersor pockmarks'for 2 hours or longer, for, if the filler had a preferential amnity for the Water at such temperature as against the bitumen similarly heated, water would be carried into the coating and blisters `and pockmarks would be produced under the conditions of the test.

When it Vis, desired to test the water resistance and non-water absorptiveness of a layerof coating composition of any given thickness desired or `utilized in a roofing embodying this invention,` the test may be made in an analogous Way, namely, by applying va layer of the composition and of the thickness in question to a non-porous sheet such as metal, e. g., aluminum, and immersing the sheet with the coating adherent thereto in Water at about 185 F. The layer is regarded as adequately resistant to water, at ,185 F. if it can be immersed in the Waterat such temperature for 2 hoursr orlonger, Without developing blistersfor pockmarks, and the layer has preferred non-water absorptiveness and Water resistance if it can be immersed in the water for 10 hours without developing blisters or pockmarks. When reference is made to a bituminous coating or layer having resistance to water at 185 F. it is to be understood that resistance of the coating or layer under the described test conditions is intended.

The coating material was likewise tested for i the purpose of ascertaining'its stress-strain characteristics both at normal temperatures (77 F.) and at elevated temperatures corresponding approximately to maximum roof surface temperatures (170 F.). In carrying out the test a specimen 1 cm. x 1 cm. x 3 cm. (between the clips of the testing machine) was used and the test was carried out on a standard ductility testing machine for bituminous 4materials (A. S. T. M. Standard 13113-39) in combination with an indicating scale balance for measuring the stress. The tension head of the ductility machine moved lat a rate of 5 cm. per minuteand the specimen was kept immersed in water maintained at the specifiedY temperature throughout the test. The tensile strength value was obtained directly from the scale reading at break in grams per sq. cm. When tensile strength is referred to herein the tensile strength as thus determined is intended. The ultimate elongation at rupture of the specimen was indicated o n an autographic record and calculated in percent elongation. When percent elongation is referred to hereinthe percent elongation as thus determined is intended. The" total Awork done in stressing the specimen to rupture was derived by plotting the percent elongation at each increment of stress untilthe breaking point Was reached to obtain the stress-strain curve of the specimen and then determining from the area between the stress-strain curveand the elongation axis of the graph the work done in gm.cm. per cu. cm. Where totalwork done at rupture or, more briefly work capacitance is referred to herein the value determined as above The total work done to rupture the asphalt sample dropped from 2064 gm.cm. per cu. cm. at 77 F. to 9.5 gin-cm. per cu. cm. at 170 F. When 40% of asbestos dust was mixed with the asphalt the tensile strength at77 F. was increased i. e., to 7100 gms. per sq. cm. but what-is most significant is that tensile strength at 170 F. was increased by the presence of the asbestos dust about 24 times, namely to 358 gms. per sq. cm. Similarly the total amount of work done to effect rupture at 170 F. was increased to 153 gm'. cm. per cu. cm.- Thus it is apparent that while the asphalt itself had no appreciable strength or toughness at temperatures such as 170 F. the presence of asbestos dust in an amount such as 40% afforded for the blister barrier coating a material retaining very considerable strength and toughness attemperatures such as 170 F. so as to resist blister occurrence therein. 1

While very high blister resistance can be achieved using about 40% by weight of asbestos dust as in the example given above, high blister resistance can be attained using lesser amounts of asbestos dust. Thus, when 30% by weight of asbestos dust is employed in the same asphalt the coating composition at 170 F. has a viscosity of 4.97X" poises and a tensile strength of 190 gms. per sq. cm. 'I'he work to produce rupture at 170 F. is 89 gm.cm. per cu. cm. The fire resistance of the coating composition is correspondingly reduced. and especially from the point of` view of re resistance use of only 30% of asbestos is a non-preferred embodiment of this invention. Still lesser amounts of asbestos dust such as about by weight are somewhat efllcaceous from the point of view of blister resistance in connection with a bitumen of the character referred Vto but do not afford desirably great re resistance.

For preferred results the tensile strength at 170 F. of the bituminous material for the blister barrier should be at least about 150 gms. per sq. cm. and the work 4capacitance of the material at the same temperature should be at least about 70 gm.cm. per cu. cm.

Another advantage of the embodiment of this invention which has been described above is its increased fire retardant character as .compared v,

1 tive of the weight of the roofing material or the .number of layers or plies that are applied to the roof deck that will successfully pass the class B or class A fire retardant tests of Underwriters Laboratories, Inc., which tests are reserved for roofing constructions which are able to withstand much more severe fire exposure. We have found that when a roong such as that described hereinafter. e. g., in the form of shingles and made on an ordinary organic fiber base felt and containing about 40% of asbestos dust in the high viscosity coating, is so highly re retardant that a three layer covering for a combustible roof deck will successfully withstand exposure to the Underwriters Laboratories class A fire retardant tests. 'Ihe class A flreretardant tests are the most severe fire tests used by the Underwriters Laboratories. We have found further, that a two-layer 4(double coverage) application of our improved roofing will' successfully pass the Underwriters Laboratories class B fire retardant test.

The nrc retardant properties of the new roofing of our invention are principally due to the fact that the blister barrier coating when exposed to direct flame is very' highly resistant, even when on a roof deck having approximately a 30% incline, to owing that leaves the organic felt base substantially unprotectedyas is the case with the coating of bituminous roofings of thetype heretofore made. Moreover, the special type of coating burns less readily and chars very slowly, and after it does become charred remains in place as a strong, ilrr'n and coherent, but highly porous, mass of carbonaceous ash that has a special thermal insulating effect and that does not develop gaps or large cracks permitting the flame to excessively heat an underlying combustible roof deck. Moreover, the coating in itself is so resistant to burning that any spread of flame is prevented and the bituminous coating material ceases to burn after the flame has been removed from the roofing.

A more detailed description of the re resistance of the roong follows in connection with typical rooflngs and roofing structures shown in the accompanying drawings, wherein Fig. 1` is a plan view of prepared roofing embodying our invention in the form of an individual shingle of simple rectangular shape;

Fig. 2 is a plan view of prepared roofing embodying our invention in the form of an individual shingle of a preferred shape;

Fig. 3 is a plan view of prepared roofing ernbodying our invention in the form of a shingle strip;

Fig. 4 is a fragmentary cross sectional View on an enlarged scale of prepared roofing embodying our invention;

Fig. 5 is a sectional elevation of `an inclined shingle roof embodying our invention without showing the component layers of the individual shingles;

Fig. 6 is an enlarged sectional elevational view of a portion of the roof shown in Fig. 4, as installed;

Fig. '7 is similar to Fig. 5 except that the roofng is illustrated as it appears after exposure to flame temperatures;

Fig. 8 is a plan view of one form of prepared sheet roofing embodying our invention adapted to be installed in roll form; Y

Fig. 9 is a sectional elevation of a portion o an inclined roof deck with the roongmaterial of Fig.. 7 installed thereon, the roong material being shown with exaggerated thickness for clarity;

Fig. 10 is a plan View of a typical built-up roof embodying our invention, with parts of the different layers broken away;

Fig. 11 is a sectional elevation on an enlarged lscale of a portion of the built-up roof shown in Fig. 10 taken on the line II-l l;

Fig. 12 is a plan view of a special type of builtup roof embodying our invention in which is employed a pre-fabricated granular surface cap sheet as the weather-exposed surface layer, parts of. the different layers being broken away;

Fig. 13 is a sectional elevation on an enlarged scale of a portion of the built-up roof shownin Fig. 12; v f i Fig. 14 is a fragmentary sectional elevation of precoated felt embodying our invention used in fabricating the built-up roof shown in Figs. 12 and 13;

Fig. 15 is a side elevation partly in section of a A nre testing device for testing roofing material:

Fig. 16 is a planv view partly in section of the I. fire testing device: l

Fig. 17 is a front elevation of a test panel as sembly used in the ilre testing device;

Fig. 18 is la side sectlonalelevation 'of the fire test panel assembly; -f

Fig. 19 is a plan view of the re test panel assemblyfwith parts thereof broken awayrand Fig. 20 is a perspective View oi the frame and white heat ai' the'intenor of the brand for about one-half hour or more. If the brand burns out without igniting the combustible roof deck (made of 8" white pine boards, finished three sides, spaced about a inch apart) the roofing the test. v In the class A flame exposure testa deck sim.- ilar to the deck used in thebumingfbrand test is I covered with rooting to be tested and is subjected guard plate used in the fire test panel assembly. n

The prepared roofing material may be cut into individual shingles I0 shown in Fig. l. Preferably the rooilng material is cut into individual shingles i0 having al notch or cut-out 49 as shown in Fig. 2 or into strip shingles Il of the type shown in Fig. 3 having the recesses orslots 50 and the notches or cut-out portions 5I. Of course, shingles or the like of other shapes may also be used. In cross section the prepared roofing material appears as in Fig. 4 and comprises a base or foundation sheet I3 -of bitumen impregnated roofing felt. Overlying therooflng felt is the coating I4 of special coating material having adherent to the surface thereof and partially embedded therein the slate granules l2. Adherent to the back of the rooting material is a layer l5 y of the special bituminous coating material in which is partially embedded nely-divlded dusting material 48. Ordinarily some bituminous coating material and dusting material are employed on the back of the roong material, but these materials are not essential and are sometimes omitted particularly when the .roofing material is to be used in constructing builtnup rooting. f

In Fig. 5 is shown a typical roofing structure in place on a roof deck comprising boards I8 which serve as a support for the shingles, e. g., strip shingles Il orrindividual shingles i0. -The individual shingles may be 16 inches long overall and laid with la 5 inch exposure thereby affording triple coverage over all parts of the roof deck except for a porticnof the. spaces between adjacent shingles in each course. 'I'he component parts of the individual shingles appear in detail in the enlarged fragmentary view shown in Fig. 6.

A roong structure of the character of the example above described has extremelyhigh fire resistance. Thus a. roofing structure such as that shown in Fig. 5, namely comprising three thicknesses of preformed roofing, will withstand the class A" re retardant tests as ,prescribed by Underwriters Laboratories, Inc., in their published instructions. (Description of Test Methods to Determine Eligibility of Roong for Classications A, B and C. Subject 55. February 1, 1939.) 'I'hese tests are the burning brand test,

rthe llame exposure test and the spread of flame test. In making the class A burning brand test the roofing is installed on a roof deck 3%; feet wide by 41/3 feet long having approximately a 30 incline (5 inches perl foot) and a largeactively burning brand (weighing about 4 pounds land consisting of a three layer grid of 36 oven dried wood strips l2" x %x is placed thereon vand fanned by a twelve-mile per hour wind so that the brand burns ercely and with almost a to a flame produced by a gas burner located below the vlower margin of the deck. The flame impinges upon an incombustible apron extending downwardly `from the lower margin. of the test deck and mushrooms up around the lower margin of the deck and under the influence of a 12'-A mile per hour wind bathes substantially the full length of the upper surface of the deck covering. The gas ame isapplied for periods of two minutes with intervals of two minutes between ap-l plications, and if the test is continued for a period of one hour without igniting the combustible roof deck, the roofing passes the test.

The other class A fire retardanttest is the spread of ame test. This test is carried out under conditions which are the same as those used in the flame exposure test except that the roof deck is 3 times as long (13` ft.) and except that the flame is applied continuously. The flame bathes about three to three 1and one-half feet of the lower portion of the upper surface of the covering that is applied tothe deck and the tendency of any ilame resulting from com# bustion of material in the roof deck covering to spread beyond the area of direct exposure vto flame is noted. As long as the flame continues of the weight 'of the roong material or the number of layers or plies that are applied to the roof B fire retardant tests.

deck, will successfully pass either the class A fire retardant tests or will even pass the class The class B testsI are generally similar to the class A tests except that for example in the burning brand test the brand is much smaller (consisting of a three layer grid of 18 oven dried wood strips 3/4" x 3/4 x 6" and therefore only one-fourth l the size of the class A brand) and burns out after a much shorter timeinterval. In the class B ilame exposure test, the test is only carried on for one-half hour employing two minute yperiods of flame application with intervals of two minutes between applications, and in the class B `flame spread test the flame is permitted to spread up the roong to a point not more than 8 feet from the lower edge of the deck.

Y When ordinary bituminous prepared rooiing is subjected to the class A burning brand test,

for example, the burning brand melts the asphalt of the coating composition which, together with any filler included in the coating composition,

starts running down the surface of the roof.

'I'he melted asphalt also starts to burn and the burning asphalt in running down the roof spreads the fire. The coating material that runs down the roof leaves the bituminized organic felt base exposed which, being readily combustible, starts burning so that the re goes through the roofing quite readily and ignites the combustible roof deck ina relatively short time. y

By way of contrast our improved roofing made as above described by way of example behaves very dierently when subjected to the same burning brand test. The behavior of the roofing material as applied to a roof deck in three layers, e. g., as shown in Figs. and 6, is indicated roughly in Fig. 7. During the exposure to the flame the finely-divided heat resistant material (asbestos dust), due to its surface characteristics including its shape, size and ainity for bitumen, provides a skeleton mat in the special coating I4 and does not flow down the roof and even though the bitumen of the special coating be-l comes very greatly softened the skeletal mat persists and thereby protects the combustible material underneath. It is also advantageous that in the softened special coating material small bubbles 46 are generated primarily by heat decomposition of the asbestos dust liberating water vapor and that these bubbles expand the coating material somewhat thereby providing increased heat insulation which is effective to shield the deck from the heat of the flame. During the exposure to flame much of the bituminous material carbonizes but the skeletal mat of asbestos dust remains as a firm coherent porous ash having pronounced heat insulation efliciency distributed substantially uniformly over the roof deck. In the roof structure as a whole as illustrated in Fig. 'l the upper layer of special coating material has become expanded and has become somewhat irregular but the partially dehydrated asbestos dust together with residual carbonized bitumen has remained as a porous coherent carbonaceous ash that acts as a protective barrier against the llame. l The layer of felt I3 may be carbonized and to a considerable degree may have disappeared leaving air pockets I'l together with some residual carbonized material. The intermediate layer I4 of special coating material is also expanded, the mat of partially dehydrated asbestos dust together with the resulting pyro bitumen remaining in place. The intermediate layer of felt is charred, but is better preserved than the uppermost layer of felt. The bottom layer'of special coating material is less severely carbonized than tie upper layer anddkewise is considerably expanded. The bottom layer of felt is fairly Well preserved and the underlying board I6, if charred at all, has not become ignited. The backing layers I5, being of the special coating composition, likewise augment the heat insulating effect of the roof deck covering and decrease the tendency of the bitumen contained therein to ilow and to become ignited. It usually takes the burning brand used in making the Underwriters class A" burning brand test about to 45 minutes to burn out.' During. this time the upper surface of the uppermost layer I4 may become lred hot but the heat insulation ef-` f ticle size issignificant inasmuch as the total charringof the roofing soon ceases and the roof-y ing cools down. The behavior of the rooiing hereinabove described by Way of example under the class A flame exposure test is generally similar to that above described in connection with the class A burning brand test. Such roofing also passes the class A" iiame spread test.V s

The resistance of the .skeletal mat to displacement while the coating material is exposed to iiame is due to the surface characteristics of the particles comprised in the asbestos dust. From one aspect the external shape of the particles of the asbestos dust is believed to contribute to the flow resistance ofthe particles comprised in the coating, inasmuch as while the particles are small they are nevertheless fibrous and tend to form a stable mat for this reason. From an-A other aspect it is believed that the asbestos has the property of stabilizing bituminous material in contact with the surface thereof by an action in the nature of specic adhesion or adsorptionl and that the stabilization of films of bitumen on the surface of the small particles imparts a matting tendency such that the particles tend to form a stable skeletal mat when the bitumenin the coating is liquiiied by exposure to high temperatures. In this connection parsurface exercising a stabilizing action is much larger when the particle size is small than when the asbestos is in the form of fibers of considerable length, but excessive-subdivision is not desirable. These `characteristics are also instrumental in affording a coherence that resists Ithe development of gaps in the coating through which the flame may penetrate during the progress of the test. The expanding of the coating material and development of pores therein are due primarily to the fact that asbestos dust is selected which contains a substantial amount of chemically combined water which under the heat of the flame, becomes liberated lforming water vapor which expands the bituminous coating material.

The preformed roofing can of course be laid w1tha greater. proportion of the area thereof exposed and so that the roof covering will be composed of two layers instead of three. Such a roofing is illustrated in Figs. 8 and. 9. In Fig. 9 the roofing material is shown as installed on a roof deck with the thickness of the courses exaggerated for clarity. The preformed roofing material consists of a foundation sheet I8 of the bituminous roofing material, coated over a part of its Width with a coating I9 of the special coating composition. This material may be made up in rolls about 36 inches wide for example with sllghtly less than half of the width of the asphalt saturated foundation sheet I8, e. g., 17 inches of the width, lcoated with the special coating I9 and covered with the mineral granules 20, e. g., slate granules. This type of roofing may be laid on boards 2I of the roof deck using suitable securing means such as nails 41, the slate covered portion being exposed and the 4balance underlying an adjoining sheet as shown in Fig. 9. `Where the preformed sheets overlap they are caused to adhere to each other by a bituminous adhesive material 22 which,

preferably, is the vspecial coating composition embodying our invention. The roofing structure above described employing special coating composition embodying our invention which is highly resistant to fire, as the bituminous adhesive zz, win successfmly withstand the UnderA writers class B tests. If it is merely desired ter described more in detail hereinbelow.V

Of course :preformed shingles (either individual or strip shingles) .may also bel laid in two courses instead of three and when roofing material of the character hereinabove described byv way of example is made up into such a doublecoverage roof deck covering, lthe roonng will likewise pass the class "B tests prescribed by Underwriters' Laboratories, Inc. When a roofing is in the form of preformed shingles or shingle strips, the tabs may if desired be positively held in place by suitable ties, e. g., of metal.. or by an adhesive such as a small amount of bituminous material, but this is by no means essential.-

It is not necessary in the practice of this invention that the special coating composition Vbe preformed at the factory integral with a foundation sheet composed of -bituminized felt or the like inasmuch as the rooilng can be fabricated on the job. An example of this type of roofing is of felt and over a period of time expand laterally until the blister covers an area of many square inches or even square feet. Any such blister formation is of course very deleterious and results in premature disintegration ofthe roof covering.

y According to the present invention this type ci' blister formation peculiar to built-up roofings can be minimized. The built-up rooflng is likewise re resistant. Thus the built-up roofing if made using conventional methods and materials would only pass class C" iire retardant tests whereas the roong above described will pass the class A tests. In 'order to increase the nre resistshown in Figs. 10 and l1 which illustrate a typicai build-up roofing. The roofing is shown installed on wood sheathing 23 to which is sei cured as by suitable nails 25 a single thickness of building paper 2t suchv as red rosin dry sheet. Two thicknesses ci bitumen impregnated felt 26 are secured overlying the building paper by nails d5. A layer of bituminous waterproofing 21 is then applied by mopping it on while in a heat liqueiied condition but instead of using ordinary inopping asphalt a specialcoating composition, e. g., containing about 80% of asbestos rust as described hereinabove, is used and in each'layer the mopping asphalt weighs about 25 to 40 poundsper 100 sq. ft. In applying the special waterproofing it should be applied while heated to about 450 F., i. e., at .asomewhat higher temperature than the temperature employed in applying ordinary mopping asphalt and to keep the composition uniform an agitator is preferably used in the heater. To facilitate application the special coating composition is preferably mixed on the job mixing preheated asbestos dust with vmelted bitumen. A layer 28 of bitumen impregnated felt is next deposited on the waterproofing 21 while it is still adhesive. Another layer 29 of the special waterproofing is then installed followed by a top-layer 3U of bitumen impregnated felt and a top layer 3| of the special waterproofing composition. Mineral granules 32 may be disposed over 'the surface of the layer-while it is still adhesive and caused to be embedded in the surface.

A built-up roong of the character above mentioned will `be found to be very resistant both to blistering andy to fire. If the cap sheet com-- prises a coatingfor weather exposure, which coatving has the high strengthv and viscosity above mentioned vatsurnmer sun roof surface temperaturcs, this coating will be highly blister resist-- anti `suflicient strength and viscosity to 'prevent blister 'j formation therein. Built-up roongs heretofore m'ajde'are susceptible to blistering not only on the weatherv exposed coating of the cap sheet but also in underlying coatings.

Moreover. any underlying coating will have up roongs blisters occur between layers or strata Frequently in builtance of built-up roonngs it has heretofore been the practice. to place thereon large amounts of mineral, i. e., as much as 3.00 to 400 -pounds per square feet of roofing area. It has also'been proposed to employ asbestos felt in the fabrication of the roofing. According to the present invention high fire resistance is achieved without resort to such expedients and using considerably less felt in the roofing as a whole.

A modified form of built-up roofing is illustrated in Figs. 12, 13 and 14. The roofing is shown installed on wood sheathing 33 over which is secured a single layer of building paper 34. Overlying the building paper 34 is a layer 35 of bitumen impregnated felt which instead of being uncoated as in the embodiment shown in Figs.

able mopping asphalt layer 31 may be employed.-

The mapping asphalt maybe a light application of ordinary mopping asphalt inasmuch as the flreresistance is' afforded by the special coating composition that is preformed with the felt sheets 35 and 3B. However, it is preferable that -the adhesive waterproong that is applied by mopping be'composed of the special re resistant composition of the character herein described so that the roofing will have maximum fire resistance. In a similar way by a waterproof adhesive layer 38 the cap sheet 39 is bonded in place. The cap sheet comprises a coating` 4| oi' the special coating composition preformed therewith to which are adherent mineral granules 40, the cross section of the cap sheet being similar to the section shown in Fig. 4 except that the back coating layer I5 .is ordinarily omitted. This type of built-up roong likewise may be made s'o as to have extraordinarily high blister resistance and re resistance. In the case of built-up roofings, such roofings may be improved as to blister resistance according to thisinvention without necessarily increasing the re resistance by emposite sheet 35, and/ or as the corresponding layers of composite sheets 36 and 39 in Fig. 13, and/or as the adhesive layers 31 and 38 in Fig. 13, special high viscosity bituminous compositions of the character herein described -which are not formulated so as to be highly re resistant.. For example, the special bituminous composition may be .a high viscosity bitumen used with little or no ller or may be a bitumen containing a filler such as gas carbon black which does not substantially increase the re resistance of bituminous compositions with which it is used but is effective to form a high viscosity coating having high blister resistance. 'I'he formulation of such spe-V cial compositions will be described more in detail hereinbelow..

Referring further to Fig. 13 the composite sheets 35, 36 and 39 may be preformed so as to carry a substantial layer of special coating composition which is both blister resistant and fire resistant, e. g. coating compositions of the character described in the foregoing example. In

order to bond such preformed composite sheets together a bitumen may be used having a. vis-A cosity of about 4x107 poises or higher `at 170 F., e. g. a. bitumen having a softening point above about 300 F., as the layers 31 and 38. In this a name against an inclined specimen of bituminized felt carrying the coating material to be tested under precisely controlled conditions determined by the construction and operation of the testing apparatus.4 Y This test which we have originated is suitable for testing roofing materials without actually carrying out the extensive fire retardant tests prescribed by the Underwriters Laboratories, Inc'., which are on a much larger scale and involve much more labor and expense. The test while not a full substitute for themore elaborate tests prescribed by the Underwriters Laboratories is capable of giving precise and reproducible results that are indicative of there retardant properties of the roofing that would be determinable under the Underwriters tests and this has been demonstrated in connection with roofing materials of the character described herein. The following is a description of the controlled conditions of the test, reference being made to Figs. 15 to 20 of the drawings:

Samples of material to be tested are `made by applying bituminous coating material to an asphalt saturated felt base sheet so that the coating Weighs pounds i2 pounds per 100 sq. ft. No granular material or the like is applied to the surface of the coating. The saturated felt base sheet Weighs about pounds per 100 sq, ft. and issaturated to the extent of about 175% by weight of the dry felt with asphalt having a softening point of about 150 F. The bituminous coating material is applied by coating the felt in the machine direction of the sheet and the felt is applied to the test deck so that the machine direction of the sheet is parallel to the direction of ame travel.

The test is made in the wind tunnel 53 having a fan 54 at one end and a stack 55 at the other end. The tunnel is made of 1A inch thickness asbestos-cement lumber and/has two windows 56 and 51 therein which can be opened and closed by any suitable means (not shown).

Within the tunnel is the burner and testing deck which are located between two shields 58 and 58 of the asbestos-cement lumber spaced 12% inches apart, and which are rigidly mounted on a steel slab 43. The inclined test deck is indicated generally by the reference character 59 and comprises a lower iron frame-like memterial 13/4 x 12 x 1A inches are placed. This com-` bustible material is what is known as Masonite Quarterboard and is'selected instead of wood because it can be obtained'with greater uniformity than can wood. fMasonite Quarterboard is made from wood fiber by compression of the ber of a berlzed mass in the presence of its naturally contained lignin binder untilit 'has a density of about 36 pounds per cubic foot. The four center boards are dried at 180 F. in a steam oven for at least 7 days. Two full plies 12 x 12 inchesof the roong 69 to be tested and one-half ply`12 x 6 inches are placed on the combustible deck followed by an L-shaped guard plate 63 which guards the bottom edge of the roofing and of the Masonite. The assembly is held down by an iron frame 64 open at the bottom and held in place by thumb screws 65. y

After the test deck has been assembled it is placed on the inclined support 66 which has an opening in the back underneath the combustible material 62 and which has side anges 66' to protect each side of the test panel. The support 66 comprises a bafe 61 to prevent the name from licking around behind the test deck. The support which is made of iron is mounted on the -steel slab 43 which measures 12 x 40 x 1 inches. The parts for carrying the test deck are also made of iron. An .iron bar 68, 12 x 1 x 1A inches, is placed across the top edge of the deck to protect f the combustible material at this point.

ber,60 having 1A inch pegs 6I projecting'from the face adjacent the upper and. lower margins.

,Between the pegs strips 62 of combustible ma- In front of the test deck is the burner 10 com-- prising a 3A inch outs'ide diameter standard gage iron pipe with 17 holes 0.078 inch in diameter and 1/2 inch apart -disposed at an angle that is parallel with the plane of the test deck. The burner has one inlet 1I controlled by valve 12 and another Vinlet 13 controlled by valve 14.

The dimensions of different parts of the testingapparatus shown on the drawings as used by us are as follows:

Inches Inches a 24 o 8 b 38 p 2 b' 6 q TA c 18% r 1 d 72 `s 12 e 161/2 t 7 f 10 u 101/2 g 121A v 12 h 38 w 12 i 64 a: 1 7 32 y 12 k 24 y 1 l 24 z 6 m 40 aa 12 n 27 bb 1 In carrying out the test the apparatus is rst assembled and the burner is lighted, the valve 12 being opened and 'adjusted until a pilot flame is produced that is about 1/2 inch in length when the fanis operating. The windows 56 and 51 are then closed and the room in which the apparatus is placed is arranged so that there will be relative constant conditions during the test. The temperature and relative humidity of the room may suitably be approximately 60 to 85 F. and 30 to 50% respectively. The fan should generate a wind velocity of about -155 feet per minute at the portion of the deck exposed to the flame. The valve 1,5 is then opened until a flamel about 8 to 9 inches long is produced having a temperature of about 1325-1370 F. When the valve 15 is opened to increase the name a timing device is started.

In carrying out the'test as above described the heat ot the flame rst softens the bituminous coating material and with ordinary roof coating materials used on prepared rooting products at present on the market the bituminousrcoating material including any ller disposed therein becomes displaced from the felt base sheet and ows down leaving the base sheet material substantially unprotected with the result that the organic telt material of the roofing in the test panel is consumed and the heat of the ilame strikes through so that the combustible panel deck relatively soon becomes ignited. However, when the plies of the asphalt saturated felt base sheet material are coated with special coating composition according to this invention, the test samples behave in a manner corresponding generally with the behavior hereinabove described of roofing material embodying our invention when it is subiected to the Underwriters' Laboratories class "A" burning brand and flame exposure tests. The finely-divided asbestos dust or the like instead of flowing down the inclined test panel when the bitumen in the coating material becomes heated and softened by the ilame resists the tendency to ow down the panel and provides a skeletal mat which remains in place as a coherent heat insulating mat-like mess in an amount adapted to effectively protect the underlying combustible test deck from the heat of the ilame for a considerable period of time. Some of the bitumen in the coating may flow somewhat but most of it is retained in the skeletal mat which persists in place and resists displacement and remains as a protective covering. Eventually during the test the bitumen becomes hardened by carbonization and contributes to the coherence and toughness of the mat-like protective mass that remains. During the continuance oi the test coating material having high fire retardant properties according to this invention continues to protect the combustible deck material from the heat of the llame so that the combustible deck does not .ignite even under the very severe conditions of the test for prolonged periods of time, e. g. 40 minutes and upward of two hours or more. The resistance to ow of the finely-divided asbestos dust or the like is due to the surface characteristics thereof which have been discussed more fully lhereinabove -and is such that a stable coherent skeletal mat is provided which aii'ords heat insulation against the heat of the flame.

The proportion of the nely-divided illler material that is used in the coating composition and the properties of the bitumen of the character herein mentioned with which it is mixed may vary, but in any event the proportion of nelydivided illler to bitumen should not be so great that the composition cannot be spread in a heat plasticized condition in a substantially uniform layer weighing about 30 to 60 pounds per 100 sq. it. on sheet material by means of a doctor using conventional coating machinery of the type used in the manufacture o: prepared asphalt rooilngs. Any bituminous composition which can be so spread is referred to herein for the sake or brevity as a spreadable coating composition. As mentioned more in detail elsewhere herein, the amount of bitumen binder should not be less than about 45% by weight of the bituminous coating composition inasmuch as coating compositions containing lesser quantities of bitumen donot have the desired spreadability. On the other hand. in the case of certain nller materials coating compositions containing them may be somewhat lacking in desired spreadability, even when the coating composition contains a greater p'roportion than 45% by weight of the bitumen. If a finely-divided illler material, when used in a coating composition in an amount which does not render the composition non-spreadable, is, due to its surface characteristics, suiilciently resistant to now to provide a stable skeletal mat that, under the conditions of the test above described, protects the combustible deck from ignition for a period ot about 40 minutes or longer, the nller material is regarded as flow resistant, as this term is used herein, when the bituminous composition in which the finely-divided filler is contained is exposed to--ilame temperatures. In such case the finely-divided illler material has the special property of resisting the tendency to ilow down the test panel when the bitumen is melted due to exposure to the llame temperature and of persisting in place to provide the high resistance to llame exposure indicated by the test, and the test which we have devised and described above enables 'one to readily ascertain this flow resistant property of suitable ilnely-divided filler materials.

The behavior of rooings embodying this invention may be contrasted with the behavior of the coating material used on ordinary roofings under the test conditions above mentioned. Ordinary asphalt impregnated roofing felt which weighs'about 30 pounds per 100 sq. ft. and which is not protected by any waterproofing coating will prevent the combustible deck material from ign'iting -for about 18 minutes. If the felt is coated with ordinary coating asphalt having a softening point of about 230 F., (the coating weighing for example about 25.pounds per 100 sq. ft.) the coating asphalt being itself combustible promotes the combustibillty of the felt and the test can be run for only about 13 minutes without igniting the combustible deck. If ordinary illling vmaterial such as slate dust is including in the coating material (the coating composition containing for example about 35% of the slate dust) the combustible deck will ignite in about 17 minutes showing that the slate dust is Wholly ineffective to afford ire retarding properties. Slate dust is speciflcally mentioned since slate dust is the illler most extensively used by the industry for the coating material used on bituminous roongs. Notwithstanding the presence of the slate dust the bituminous coating ignites readily and becomes displaced from the felt so that the roofing rapidly disintegrates and permits the combustible deck used in the test to become ignited after only the short period of time mentioned. Limestone dust when used as a illler behaves very similarly to the slate dust. Materials such as white lead, asbestine and pyrophyllite talc likewise have little effectiveness.

It is apparent from the results of the test above mentioned that according to the present invention-one can readily double nre resistance as nary temperatures.

compared with the nre resistance of ordinary rooflngs made at the present time and in preferred embodiments of this invention one can increase the re resistance of rooiings many times more.

Hereinabove emphasis has been placed chiefly on the blister resistant and iire resistant properties of the rooings embodying this invention.'

It may also be mentioned. however, that rocngs having these advantages can be made according to this invention without sacrifice f other desii-ed properties and even with resulting improvements in other respects. Thus roongs embodying the special coating material can be manufactured which have adequate pliability at ordi- Roong material made according to the previously described preferred example can be bent 180 in 2 seconds around a 2 centimeter diameter mandrel with the blister barrier coating on the outside without, cracking of the coating through to the felt base, the test being made at 77 F. The roofing as above described has the advantage of being somewhat stiffer at normal temperatures than ordinary as- .phalt roofings heretofore manufactured. While it is possible to achieve very high pliability at normal temperatures in the practice of this invention, one can achieve the advantages of this invention i'n roofings which have somewhat less pliability at normal temperatures, e. g. 77 F., but which still have sucient pliability at normal temperatures for most commercial pui-poses. It is desirable that an asphalt roofing be at least sufficiently pliable to be bent 180 in 2 seconds around a mandrel of centimeters diameter at 77 F. with the coating on the outside, Without cracking the coating through to the base on which it is applied and any such coating or layer is referred to herein .as pliable at ordinary temperatures.

The new roofing of this invention described in the foregoing example is likewise less brittle at lower temperatures such as .50 and 32 F. than roofngs heretofore made, and can be applied in cold weather better than such roongs.

The new roofing described in the foregoing example also exhibits an increase in strength and toughness as compared with ordinary roongs of substantially the same weight, the increase being in the order of about when subjected to the Mullen bursting test (with the coating for Weather resistance outward) or to conventional tensile strength tests at 77 F.

It may also be mentioned that the new roong of the previously described example exhibits improved ability to hold the embedded granular surfacing material in the coating layer during weather exposure because of the toughness and strength of the high viscosity bituminous coating resulting in decreased tendency `of the surfacing material to loosen or shed under weathering conditions as compared with ordinary bituminous roongs.

In addition to the foregoing properties and characteristics of rooflngs embodying this invention, mention also should be made of the highly important fact that the new roofing can be made on conventional roofing machinery and that the special coating can be applied by a conventional roofing coating operation. It is of great practical importance that the special composition comprises asbestos dust which does not interfere with the spreading of the special coating composition' uniformly on the felt with the asbestos dust distributed as a uniform mat-like mass therein.

In. the manufacture of roong according to the present invention utilizing the method and apparatus described in our Patents Nos. 2,105,531 and 2,159,586 it is not essential that the felt base be sealed' with the special cating composition. For example, the felt base may first be impregnated with a bituminous saturant then sealed in a devoided condition with ordinary coating asphalt having a softening point of about 220 to about 240 F. Thereafter'the filled and sealed iveb could have a coating of the special coating composition applied tothe surface thereof and thereby afford the advantages of a blister resistant coating or barrier for the roofing which coating or barrier preferably is also re resistant. Moreover, instead of devoiding the brous web base to as low as about .5% as described above, a void content ofthe fibrous web base and of the roofing of less than about 2% affords good resistance of the fibrous web base to penetration by moisture and to the deleterious action of moisture and is regarded as being substantially non-porous.

While it is preferable that the blister barrier coating or layer be carried by a felt base that has been filled and sealed in the manner described in our Patents Nos. 2,105,531 and 2,159,586 this is not essential. For example, roong that is manufactured merelyv by rst impregnating the roong felt with abituminous saturant having a softening point of about 11.0 to about 160 F. and then applying the special coating material having high lviscosity at summer sun roof 4surface temperatures according to the present invention to the felt which is still porous, e. g.

containing about 10 to 20% of voids, exhibits greatly improved resistance to blistering as compared with roongs utilizing ordinary biturninous coating material applied to a similar felt base because the special coating has such high strength and resistance to deformation that vapor pressures generated by moisture entrapped in the porous felt base by summersun temperatures do not deform the coating and form blisters in or under the coating layer. The roong as thus prepared has somewhat less resistance to the boiling Water test than the roofmgs described in the preceding examples, but this is due primarily to failure of the roofing .felt at the back of the Vroofing ratherthan to blister formation in the special high viscosity coating. Many roofings fail on Weather exposure due to disintegration of the felt at the back of the roofing and for this reason it is preferable to utilize the method and apparatus of Patents Nos. 2,105,531 and 2,159,586 in the manufacture of roofing according to the present invention so that the surface coating will be blister-resistant and at the same time the felt base will not deteriorate prematurely and will have as long a life as the blister-resistant coating. A roofing made without utilizing our prior patents will have the fire resistance, pliability, strength and toughness that are incident to preferred embodiments of this invention above described.

While it is preferable to employ a ller in the blister barrier bituminous coating or layer it is not absolutely essential to do so while still obtaining improved blister resistance according to this invention. Thus a high viscosity coating can be used which merely consists of bitumen which has been refined and oxidized to a much higher tumens heretofore used in the manufacture of prepared asphalt roongs. In such case it is preferable that thelsoftening point be as high as about 300 F. (ball-and-ring) te impart high blister resistance and to. afford a roofing that will withstand summer sun roof temperatures as high as about 170 F. The viscosity of such bituminous material is about x10'l poises at 170 F.

assuma For' withstanding summer sun temperatures` somewhat below about 170 F. such as are encountered in the northern half of the United States orv for affording somewhat less blister resistance at higher summer sun temperatures, a

coating of bitumen having a viscosity of abou 4.0x10".poises at 170 F. may be used. l A roofing which comprises ablister barrier coating consisting substantially/entirely of bitumen having high viscosity at summer sun roof surface temperatures is not as satisfactory as the yembodiment of this invention containing asbestes dust as a filler, inasmuch as while the l has been brought -to the proper viscosity by heat and oxidation and to use bitumens derived from Mid-Continent petroleum in order to achieve as high resistance to weathering as possible, but

such bitumens have the disadvantage of being the staining type that causes discoloration of many but not all mineral surfacing granules that are embedded in the coating asphalt layer. It is possible in the practice' of this invention to incorporate a flller such as asbestos dust'in a bitumen such as bitumen having a softening point greater than about 275 F. or even greaterl than about 300 F. and thereby obtain greater toughness, pliability, fire resistance and some increased resistance to weather exposure. It is not necessary, however, when a filler such as asbestos dust is used to employ a bitumen that has such a high softening point (before incorporation of filler) in order to obtain a high viscosity coating that is resistant to blistering. As mentioned '4 above by using a. bitumen that has a softening point of about 220 F. to about 240'? F. and using asbestos dust therewith so that there is about 30% of the asbestos dust in the coating as a whole, the viscosity of the coating can be raised to 4X 10"' poises or higher at 170 F. and to a softening point of about 320 F. By thus utilizing a bituminous material having initially a relatively low f softening point together with suflicient flllersuch as asbestos duist to afford a high viscosity, high softening point coating/material optimum conditions are obtained, namely, blister resistance `combined with high pliability at ordinary and at low atmospheric temperatures, long weathering properties and fire resistance.

Somewhat more generally, it is preferable to employ in the practice of this invention a bitumen having a softening point below about 275 F. and preferably below about 240 F., e. g., about'200 F. to about 240 F., together with a filler that is of such character and amount as to raise the softening pointto above about 300 F., although the softening point or the bitumen does not have to be qpite as -high when a lleris used as when a filler is not used. It is usually n otdeslrable to vary the softening point of the bituminous materialabove about 350 F. (either containing or not containing a ller) inasmuch as the coat-- ing material becomes undesirably stiff and brittle at ordinary temperatures and is difficult to apply by,a coating operation in a heat-plasticized semifluidstate. ,v -f

Preferably the bitumen that lis used is that which is obtained by air-blowing a residual asphalt flux from the rening of Mid-Continent petroleum or ailux of similar characteristics, such as the residuum from Illinois crude, to a softening point of about 220 F. to about 240 F. inasmuch asvsuch an 'asphalticmaterial aords a blister barrier coating having very high resistance to' weathering, combined with-good pliability.' Use of soft oily bitumens having. a softening point below about 160 F. is not recommended. Air

blown asphalts are `preferable to steam distilled ,and straight run residual asphalts vbecause of their lower temperature susceptibility. Other bituminous and asphaltic materials may also be used such as asphalts produced from the 4 refining of Mexican, Venezuelan and Colombian l crudes. Moreover, various pitches, coal tar and the like may be used in the practice of this invention, and are claxiiied, herein as bitumens, the term bitumen being used in a broad sense and as including binder materials that contain at least to. a predominant extent thermoplastic binder materials ofthe character aforesaid. It

is not essential when a filler is used that thesoftening point of the bituminous material be elevated to above300 F. if the viscosity and tensile strength are increased suiliciently to inhibit blistering. It is viscosity and strength at summer sun roof surface temperatures that are of paramount importance. As aforesaid, however, the use of bituminous compositions for the special coating having a softening point above 300 F. is to be preferred.

In addition to asbestos dust there are a number of other finely-divided fibrous asbestos filler materials, that may be used. There are various other materials such asv those referred, to aS "asbestos powder and "milled asbestos'tailings" which are highly desirable. Also available are various types of chrysotile asbestos refuse or shorts `produced in the milling and grading operations. Another fine asbestos ller which may lbe used is that which is known as asbestos air chamber floats and which is recovered by air flotation from the milling and screen grading of asbestos liber. 'I'his material is not quite as desirable as asbestos dust. These asbestos brous materials are all of line particle size and very' short fiber length. While the various types and grades above mentioned vary to some extent in grading and fneness of subdivisionv they are all such that a. major proportion will pass a f8-mesh standard testing sieve. Also with the exception of the asbestos air chamber floats, which are somewhat less desirable, they all contain at least about 50% by weight of material which will pass A filler material which is fibrous in character is preferred in the practice of this invention inasmuch as fibrous llers have greater effect in the amount used in increasing the toughness, pliability and lire-resistance of the coating.

it is preferable to employ a graded fiber mixture Moreover,

of which at least 25% is retained on a 10U-mesh sieve, at least about 35% passes a 10U-mesh sieve is used, which residue will pass a 200-mesh testing sieve, both the blister resistant and fire resistant.

characteristics of the coating material are reduced. This is believed to be due to the fact that such extremely fine material lacks the capacity to impart strength to the coating suiiicient to make the coating highly resistant to blistering and also lacks the capacity to form a skeletal matlike mass which is adequately stable and resistant to displacementwhen the coating is subjected to flame temperatures. For this reason when finelydivided asbestos is used, the coating composition should preferably contain at least about of asbestos that is retained on a 10D-mesh testing sieve.

On the other hand, the asbestos that is used should not comprise an excessive amount of fiber having considerable length. The grades of asbestos classified as fiber according to the Quebec Asbestos Producers Association are unsuitable for use in our invention because their average length is excessive. Such grades of asbestos which vcontain fibers of very substantial length (and which are desirable for this reas`on for a number of other commercial purposes such as reinforcing insulation, manufacture of asbestos paper, etc.) do not lend themselves to the improved roong of this invention. The fibers tend to become entangled in clumps or clots which result in non-uniform distribution of the asbestos in the coating composition and which render it substantially impossible in a manufacturing operation to apply the coating material without producing a product of non-uniform thickness and having an unsatisfactory irregular surface texture and therefore commercially unacceptable. These irregularities likewise impair the Weather resistance and durability of the roong on exposure and also impair the iire resistance of the roofing. For these reasons the coating material preferably should not contain more than about 10% by weight of the total asbestos content that is retained on a 14-mesh sieve.

Considering then the matter of fiber siZe,-it is preferable in achieving blister resistance and in achieving iire resistance to employ fiber which passes a 1li-mesh testing sieve and a substantial portion of which is retained on a G-mesh sieve, a major proportion being retained on a G-mesh sieve. A somewhat wider range is, however, permissible, namely, passing a 10-mesh testing sieve withv a major proportion retained on a 200- mesh testing sieve. When it is stated herein or in the claims that the bituminous composition contains a minimum percentage of fiber or other ller which passes a 14-mesh (or a 10-mesh) testing sieve and a major proportion (over 50%) by weight of which is retained on a 20G-mesh testing sieve, reference is made to the defined filler material as being of particular effectivevness foruse according to this invention but without necessarily excluding the presence of additional ilber or other filler that 'is outside of this definition. Thus, in the example of this invention that was given hereinabove, the bituminous composition of the waterproofing layer contained 40% by weight of asbestos dust, all of which passes either a 14-mesh (or a 10-mesh) testing sieve and substantially 50% by weight of which is retained on a ZOO-mesh testing sieve. Such a bituminous composition is to be understood as containing 40% byweight of ller which passes a 14-mesh (or a 10-mesh) testing sieve and a major proportion of which is retained on a. 20D- mesh testing sieve, and a bituminous composition is to be understood as containing this same per- ,centage of such effective flller material, if, in

addition to this percentage of effective fillerv material, there may be present som'e additionalfller that passes a ZOO-mesh testing sieve orsome Coarse material that is retained on a 10- or on a 1`4-mesh testing sieve.I More concretely, and merely by way of example, if there is available a supply of asbestos dust all of which passes a 14- mesh testing sieve and containing 50-51% by weight of particles retained on a ZOO-mesh testing sieve, and a bituminous composition is formulated using 40% by Weight of the composition of this asbestos dust, the resulting composition obviously contains 40% by weight of finely-divided mineral ller which passes a l4-mesh testing s ieve and a major proportion (over 50%) by weight of which is retained on a 20G-mesh testing sieve regardless of the balance of the composition which may consist entirely of asphalt or may consist of asphalt together with some other filler such as asbestos retained on a l4-meshtesting sieve and constituting say, 3% by weight of the composition, and/or such as asbestos powder, hydrated Portland cement powder, or the like,

`all passing a 20D-mesh testing sieve and constituting say, 5% by weight of the composition. In a composition of the proportions just mentioned, the 3% by weight of asbestos that is retained on a 14g-mesh testing sieve and the 5% by weight of additional ller all passing a 20o-mesh testing sieve merely constitute surplus filler in the composition which as aforesaid, contains 40% by weight of filler which passes a 14-mesh testing sieve and a major proportion (over 50%) by weight of which is retained on a 20D-mesh testing sieve. The foregoing applies to other llers and filler mixtures and to percentages of filler -content other than 40% that are mentioned l When finely-divided fibrous asbestos dust is reinforcing fine asbestos is coated on metal, the

coated metal can be immersed in water at F. for -10 hours or longer without exhibiting any tendency for the asphalt coating to blister.

stand the immersion test in water at 185 F. but v generates blisters intermediate the thickness thereof. For the same reason highly water-absorptive mineral fillers, e. g. bentonite, are rela'- tively undesirable. Those fillers that are porous, such asdiatomaceous earth or which have high surface affinity for water such as` calcium carbonate and' lpulver-ized silica (quartz), are also undesirable particularly when used with a bituminous material of relatively low softening point, e. g., a softening point of about 240 F. Watersoluble iiller materials are undesirable. In general, it is preferable to employ a non-porous fibers of other types when of the nneness of "size or grading above specified and which contain `water of constitution liberatable at ame temperatures, are preferable for use in our invention forthe same reason. Another brous material,` Canadian picrolite, which alsoy has these properties, comes within the m of they term asbestos as used herein and may also be used when of the oneness or subdivision hereinabove.

described. There are other fibrous minerals -of the asbestos group which have low liberatable combined water and therefore do. not liberate water vapor at flame temperature, but which are ,l

suitable, in the finely-divided condition above de-v scribed, from the standpoint of blister resistance and forming a flow resistant and coherent skeletal mat that is fire resistant. Such additional water-insoluble mineral ller that has a preferential aiilnity for bituminous material rather y 4 than for water in order to provide a non-waterA absorptive bituminous composition.

Fillers such as limestone flour and slate flour do not appear to have the capacity to increase viscosity and 'tensile `strength to desired extent.

Limestone flour and slate flour are prepared by pulverizing natural limestone or slate. Representative specimens of these ller materials con-f taining over 80% of particlespassing a 1D0-mesh testing sieve were mixed with asphalt having a softening point of 231 F. Even when as much as4 40% of these fillers were used the viscosity at 170"4 F. was only .8X107 poises and additional quantities of these ller materials within the limits of workable consistency of the composition did not materially increase the viscosity at 170 F. of the bituminous material. Thus 50% of limestone flour gave a viscosity of only :81X 10" poises at 170 F. The tensile strength at 170 F. using 40% of limestone iiour and slate flour was 60 gms.

per sq. cm. and 'l5 gms. per sq. cm., respectively, and the work capacitance at 170 F. was slightly less than 22 gms-cm. per cu. cm. for each. It is therefore apparent that limestone flour and slate flour even though very finely divided lack the effectiveness of the asbestos dust to afford high viscosity andu high strength whereby blister resistance can be achieved. Moreover, the materials containing limestone flour or slate our could not, when coated .020 inch thick on metal, be immersed in water at 185 F. for half to three quarters of an hour without blistering, indicating excessively low resistance to water absorption.

Of the filler materials that may be used in the practice of this invention chrysotile' asbestos shorts or dustl are preferred. This material affords a coating which is highly resistant to moisture penetration and is adapted to increase the strength of coating compositions so that they are substantially impervious to blistering at summer sun temperatures. In the second place the material has the capacity tov form a stable and coherent skeletal mat that is highly flow resistant at flame temperatures. In the third place, this -material contains water of constitution liberatable at temperatures adjacent flame temperatures which, by formingpores when the composition is subjected to llame temperatures, greatly Portland cement.

increases the thermal insulating effect of the abestiform mineral ibers` include crocldoliteI amosite, anthophyllite, tremolite and actinolite.

Another material which is excellent from the pointof view of affording blister resistance and l also re resistance is finely ground asbestos cement scrap. Asbestos 'cement rooilngs usually contain about 20% to 35% by weight of asbestos fiber and 65% to 80% by weight of hydrated Heretofore such scrap material has been regarded as an unavoidable waste of no commercial value. However, by subjecting such scrap material to aldisintegrator such asa hammer mill until it at least vpasses a 10-mesh testing sieve and preferably passes a `lll-mesh testing sieve and until about 50% by Weight passes a 1B-mesh testing sieve, a material is afforded which when incorporated, e. g. to the extent of about 30% to 45% by weight of the coat- -ing composition affords a rooiing whichl is very highly blister resistant and islikewise very highly lire resistant. Preferably a major proportion of the ground asbestos-cement scrap is retained on a 20G-mesh testing sieve. Thus if a coating composition containing for example 35% of the nely ground asbestoscement scrap and asphalt having a softening point of about 230 F. is applied to an aluminum panel, the panel can be inserted in Water at '185 F. or even in' boiling water, for 24 hours and longer without exhibiting any blistering tendency, thereby indicating its very high blister resistance and resistance to moisture penetration. The effectiveness of asbestos-cement scrap is due partly to the fibrous character of the particles and to the fact that the fibers carry nodules of the cement thereby affording a highly stable mat` in the coating` which renders the coating both fire resistant and blister resistant. Moreover, both the asbestos and the hydrated cement have an aflinity for asphalt which is preferential to water even at elevated temperatures and which stabilizes asphalt films on the .surface thereof so as to impart flow resistance at flame temperatures. Likewise both the asbestos and the Portland cement give oifwater of constitution at elevated temperatures which contributes to fire resistance as has been mentioned more in detail elsewhere, herein. Hydrated 'Portland cement contains about 15% to about 20% by Weight of-water of constitution which is liberatable at temperatures somewhat below flame temperatures, namely, at temperatures above about 800 F.

\ In addition to asbestos-cement roofing scrap other sources of mixed asbestos and hydrated Portland cement in the finely-divided form above described may be availed of. Mixtures of asbestiform mineral fibers witlrhydrated Portland ce- `verization, so as to vpass a f8-mesh testing sieve.

Particles which are retained on a 14-mesh testing sieve are undesirable. Hydrated Portland cement 'of such fine particle size will by itself serve to impart quite high blister resistance but not as high blister resistance as ground asbestos-cement scrap or asbestos dust when n corresponding amounts of mineral 'filler are used in a coating composition. Hydrated Portland cement also imparts some fire-resistance to roongs but not as highgfire resistance as ground asbestos cement scrap or asbestos dust.

Another material which is analogous to-hydrated Portland cement in the extent to which it imparts both blister resistance and fire resistance to the special coating compositions is powdered serpentine rock. This material is especially effective when produced so as to pass a li8-mesh testing sieve and be retained on a 200- mesh testing sieve and shouldpass a 14-mesh testing sieve. and powdered serpentine rock` are not fibrous in character they nevertheless have the capacity to provide a stable and coherent skeletal mat that is iiow resistant when the coating material is exposed to flame temperatures. This property is believed to be due primarily to the fact that these materials have the property of stabilizing films of bitumen in contact therewith. Powdered serpentine rock, like hydrated Portland cement, contains water of constitution liberatable adjacent flame temperature and this property also contributes to the fire resistance of bituminous coating compositions containing them.

Somewhat more generally the requirement that the coating material comprised by the new roofing provides a protective skeletal mat when the coating is subjected to flame temperatures is the result of surface characteristics of the small heat resistant particles contained in the coating material, i. e., the shape and size thereof and/nr interfacial action between the particles and the bitumen which stabilizes bitumen lms in contact wit-h the surface of the particles. Any nelydivided heat resistant material, the particles of which have such surface characteristics as to be flow-resistant, lmay be used to afford a roofing having high fire resistance. By he'at resistant any material which is suiiiciently heat resistant that it will retain structural integrity when subjected to llame temperature While incorporated in a roofing is intended. In this connection asbestos fibers, hydrated Portland cement, picrolite, etc., which contain water of constitution that may be driven olf at temperatures adjacent flame temperatures are regarded as heat resistant.

The iinely-divlded materials hereinabove specifically rrentioned have utility both because of theirA capacity to increase blister resistance and because of their capacity to increase fire resistance. In addition there are certain mineral ller materials which, While they donot materially increase the fire resistance of roofing nevertheless can be used so as to produce a coating having such strength, viscosity and Water impermeability at summer sun roof surface temperatures as to be highly blister resistant. Gas carbon black produced by pyrolytic decomposition of natural gas by the well known channel process While hydrated Portland cementv 170 F. and a tensile strength of 455 gms. per I sq. cm. at 170 F. The work capacitance at 170 F. was 173.5 gm.cm. per cu. cm. When a coating .02 inch thick was applied on metal the coating would be immersed in ywater at 185 F. for far in excess of 10 hours without blistering. Gas carbon black is usually very finely 'divided and 100% will pass a 10U-mesh testing sieve.

summarizing the foregoing, those finely-dlvided mineral materials Which can be preferably used according to this invention so as to afford roofings Whi-ch are both highly fire resistant and highly blister resistant are finely-divided asbestiform mineral fibers and finely-divided asbestoscement scrap or other mixtures of asbestiform mineral fibers with hydrated Portland cement. Other examples of finely-divided mineral fillers which can be used to afford both fire resistance and blister resi-stance are hydrated Portland cement and finely-divided serpentine rock. A material which provides high blister resistance but is not effective to afford reresistance is gas carbon black. If desired, mixtures of the mineral fillers may be employed. If such a mixture is used it is desirable that those materials which Moreover, it is preferable that at least about 20% of the filler be brous in character, e. g. asbestiform mineral iiber or asbestos-cement, although when about 20% lby Weight of the filler is gas carbon black the viscosity of the coating composition l's markedly increased due to the great effectiveness of this material in this regard. Preferably the materials having the effective properties above mentioned are used as the entire ller inl the special coating composition but minor proportions of other filler materials may be utilized while still-retaining some of the advantages of this invention. Of the finely-divided mineral llers which may be added as diluent `filler materials to the highly eifective filler materials labove described, kaolin clay, calcium silicate hydrate, fly ash, land plas'ter (uncalcined gypsum) and fibrous talc are to be preferred. These finely-divided mineral fillers have the property of increasing somewhat the viscosity at 170 F. and resistance to water at 185 F, of bituminous coating compositions as compared with materials such as slate flour or powdered limestone which latter are the filler materials most generally used heretofore in coatings for prepared asphalt rooiings and which do not have effectiveness in these respects. Of these materials kaolin clay and calcium silicate hydrate are finely-divided fillers of the iiow resistant type that provide a stable and re resistant skeletal mat vhena bituminous composition containing them or either of them is exposed to flame temperature. The substance fly ash is the finelydivided coal ash carried to the stack in furnaces burning powdered coal and is collected by electrical precipitation or other suitable method. It usually contains about to 100 of particles h a 14-mesh testing sieve.

passing ctl-mesh testlngtsieve-t- The Vbrous l:

n proximately 15 ypounds per 100-square feet 1n 'ortalc referred to is exemplied by that brous talc which is obtained from deposits in St. Lawrence county, New York, and sold under the name Asbestine. It is used extensively in the paint industry. f

The term mineral ller is used herein to distinguish from fillers composed of vegetable or animal material and the term "iller"4 denotes any finely-divided material adapted to be carried in the bitumen matrix of the coating material.

Regardless ci' the type of filler used it should be of the relatively nely-divided character` mentioned above,'namely, not more than l0% should be retained on a -mesh testing sieve and preferably not more than 10% should be retained on Moreover, preferably all coating be distributed 'so-as to be at leastv apder to afford strength adequate for blister resistof the material should pass a 14-mesh testing The amount of ller-that is desirable depends partly upon th-e" vsoftening point of the bitumen that is used and partly upon whether or not fire resistance is desired in addition to blister resistance. As mentioned above a bitumen having a very high softening point, that is 300 F. or above can be used without any ller as far as blister resistance is concerned but cannot be so used if fire resistance is also desired. y

When bitumens having a softening point lower than 300 F. yare used, the use of filler becomes important from the standpoint of blistering in order to impart high viscosity to the coating composition as a whole. Where a bitumen having a softening point of about 220-to 240 F. ils used the presence of about 25% to 55% by Weight of filler is usually required. When a bitumen having a softening point below 300 F. is used the filler in amount and type should preferably elevate the softening point of the mixture as a Whole to about 300 F. or higher. It is preferable that the special coating having high blister resistance contain at least about 25% by Weight of finelydivided ller material Aof the character herein described. The specific effect of the ller in increasing the softening point rand viscosity of-the bitumen depends for the most part upon the size and surface characteristics of the filler particles. Preferably the filler should be such that the desired high softening point and high viscosity is rattained when using less than about of ller in the bituminous coating composition as a whole.

Excessive amounts of filler tend to make the coating material excessively brittle and low in pliability. In order to preserve desirable pliability for roll roofing and the like, thegper cent. elongation at 77 F. of the bituminous material should be at least about 35 and preferably should For roof-lng using a porous sheet material such as felt impregnated withv a bituminous saturant and containing about 5% to 10% voids therein ance in high degree. `Where the coating is applied over a non-porous base material such as metal or felt that has been filled and sealed in a substantially completely devoided lcondition Aby the use of the method and apparatus of our Patents Nos. 2,l05,53l,and 2,159,587 the coating may be quite thin, e. g., about 10 pounds per 100 square feet. At the other extreme the blister barrier coating can be applied so as to be very thick and can be applied in one or more layers.

From th'e standpoint of lire resistance there should be present in the roong sufllcient mineral filler having thesurface characteristics above referred to not only to provide'a residual skeletal mat which remains in place when the roofing is exposed to flame temperatures, but also to provide a residual skeletal mat that has deflnite heat insulating capacity. Thus in the foregoing example comprising three thicknesses of preformed shingle material each thickness of the preformed material carried about 50 pounds per .100 square feet of coating material containing the roof covering as a whole contained at least about 60 pounds per 100 sq.` ft. of roof deck covered. More generally, for fire resistance the coating material should contain at least 30% by weight and preferably at least about 35% by weight of finely-divided heat resistant material having the surface characteristics above mentioned. For high resistance to name spread at leastabout 35% by weight of finely-divided heat resistant material should be included in the special coating and preferably atleast about 40% by Weight of finely-divided heat resistant material should be incorporated. l

It is usually. preferable that the coating material contain a major proportion of bitumen although the bitumen content may be reduced to about 45% by weight. Conversely, the total amount of filler should not exceed about 55% by weight of the coating composition andl preferably is less than 50% by weight. Those compositions which contain about 40% to about 50% by weight of mineral filler are especially re resistant when the ller has the surface characteristics described herein. Such roongs are especially resistant to bleeding of bitumen from the nely-divided heat resistant material' when the coating material is exposed' to flame temperatures. Bitumen that bleeds to the surface burns more freely than when mixed with nelydivided heat resistant ller and tends to promote spread of flame. While a small amount lolf bleeding is not especially harmful, highest resistance to flame spread tests are obtained when the coating material is substantially non-bleed'- ing at flame temperatures. Usually for high fire resistance combined with high blister resistance the coating material is applied to the weather exposed side of the base sheet so that it will weigh about 20 to 'Z0 pounds per 100 sq. ft., although about 30 to 60 pounds per 100 sq.` ft. is usually preferable. i

In the coating as applied there should, in rder to afford a heat insulating mat, be present finely-divided heat resistant material weighing at least about 6 lbs. per 100 sq. ft. and preferably at -least about 9 pounds per 100 sq. ft. Inthe complete roof deck covering as applied compris-

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