CA2038576A1 - Torchable roofing base sheet - Google Patents

Abstract

ABSTRACT

A roofing base sheet for application by use of heat to an underlying substrate comprising:
(a) a sheet of a flexible material, (b) a layer of a first asphalt composition covering the underside of the sheet, the asphalt composition being liquefiable by the use of heat for application and adherence to the underlying substrate, and (c) a protective covering over the first asphalt composition to prevent its sticking, the protective covering being a pervious material or an impervious material convertible by heat to a pervious condition so that heat applied to the underside of the sheet liquefies the asphalt composition and renders any impervious covering pervious, whereby the liquefied asphalt composition can be directly applied to the underlying substrate.

Description

F3 13(!4 ~ k'N'I' r`'3,~23/9~

2 ~ 3 7 ~

TORCHABLE ROOFING BASE SHEET 1.

Back~round oE the Invention 1. Field of the Invention This invention relates yenerally to roofing systems and, more particularly, to an asphalt-coated base sheet ~hich can be torch applied to a roof surface.
. Description of the Prior Art Roofi.ng systems are well known in which a roof deck (with or without insulation) supports thereon a pluxality of layers of materials for forming a finished waterproof roof surface over an enclosed space. In comrnercial structures and other relatively flat roof structures, various materials are known and used in combinations thereon for buildi.ng up a finished roof on such structures as specified in the trade.
Ge~erally the roof deck supports an lnsulation layer of fiberboard or the llke which provi.des a rigid, continuous, flat, upper surface on which a roof covering is appliedO
One of the well known forms of constructing a roof membrane is to apply hot asphalt and roofing "felt" in multiple layers to provide the necessary strength and resistance to long-term weathering and water ponding reguired for satisfactory roofing system performance.
Conventional built-up roofs have a nurnber of shortcomings. The application of several layers of roof illg felt with the use of hot asphalt is a time consurning and labor intensive tas~ which adds considerable cxpense to the finished structure. There is a narrow temperature range in which asphalt must be heated and applied, increasing the possibility of error, such as overheating the asphalt, mopping asphalt after it is too cool to embed the plies, etc. Furthermore, this conventional application process is not free from various dangers such as r.isk o-f a fire accompanying the step of heating asphalt, possibility of human injury such as-a burn occurring during the steps of transporting and handling the hot molten asphalt, air pollution due to smoXe and fumes, and offensive smell P, 13 n~ A~ N~l~
~3/23/90 2 ~,~33~
generated from mvlten asphalt. The trouble, danger and expense of hot-mopping asphalt are exacerbat~d in metropolitan areas, especially in applications on -the roofs o tall buildings P~ popular method of ameliorating the problem involves thc combined use of a conventional base sheet and a mo~ified bitumen roofing membrane. The base sheet is either mechanically fastened or mopped in place with hot asphalt.
The modified bitumen membrane is then applied over the base sheet. A desirable method of applying the modiied bitumen is by torching the back~side of the thermoplastic roofing to cause the modified bitumen material to flow and adhere to the previously applied base sheetO Since the commercial practice of this method so often entails the hot-mopping of asphalt, there is still a need for improved roofing systems which would further reduce or eliminate the need for applying the hot and molten asphalt.
OBJECTS OF THE INVENTION
It is therefore an object of the present invention to provide an improved method which eliminates the need for applying hot and molten asphalt to adhere a base layer of a roofing system.
It is another object of the present invention to provide an improved roofing membrane which can be safely, simply and economically applied to a roof deck to provlde a highly adhesive and protective covering.
It is yet another object of the present invention to provide an improved roofing base sheet whose underside is coated with asphalt in sufficient quantity to facilitate flow of the coating asphalt upon the application of heat, and consequent superior adhesion when the base sheet is contacted with a variety of common roof deck substrates, which may include insulation, an existing roofing membrane, etc.
Other objects and advantages o the invention will be described or become apparent from the following description and claims when read in light of the accompanying drawings.

~)! 1 3 0 4 ~,4'J.' k;N'l' 7 ~3 The pxesent invention encompasses a novel roofing system wherein a base sheet is torch applied to an underlying subs-trate (e.g., a roof deck, insulation or existing roofing membrane). The asphalt-coated base sheet is coated on its underside, which contacts -the underlying substrate, with a sufficient ~uantity o~ an asphalt or bituminous composition which flows upon application of a torch so that the sheet becomes firmly adhered to the substrate. The coating can be torched in spots or over its entirety during application. The torchable base sheet thus is designed for use by spot torching as a base ~ly in specifications where venting of the substrate is desirable, and can also be fully torched in non-venting applica-tions.
The invention eliminates the need for the hot-mopped bitumen -typically employed in applying conventional base sheets over old roofs, insulation, or non-nailable decks. ~he base sheet can be used on any roof as a substitute for the conventional base sheets whose application requires the spreading of hot and molten bitumen at the job site. It can also serve as an acceptable base ply when it is mechanically fastened to a roof deck, such as a lightweight lnsulating concrete deck.
The base sheet comprises any suitable support, such as a fabric or web formed from woven or non-woven organic or inorganic, natural or synthetic fibers (staple or continuous filament), e.g., a fiberglass and/or polyester mat, at least one (the underside) of whose two major surfaces is coatable with asphalt. The support may be a suitably top-faced laminated sheet whose underside is coatable with asphalt.
The asphalt on the web's underside must be rendered li~uefiable by heat for ready application and adhesion to a roof surface. A suitable asphalt for this purpose is a blown product which is derived from an asphalt flux oil and is unstabilized, i.e., it contains no mineral stabilizer.
The surface of this li~uefiable asphalt is provided with a covering to protect against sticking to machine rolls during mamlfacture and against blocking after packaging. The covering may be a pervious material, such as an inorganic B 130~ ~AI~ENT
0~/23/90 sllrfacinfJ material (e.g., talc, sand, etc. ) or an impervious - material. The impervious covering must be convertible to a pervious state by the heat which lif~ueies -the underlying asphalt so that the melted asphalt will unimpededly contact the roof surface. A preferred impervious covering comprises a plastic film which melts when the underside is heated.
The plastic film is preferably coeY.tenSiVe and congruent with the surface of the liquefiable asphalt.
The upper sur~ace o~ the support may be uncovered, but advantageously is covered, such as with a waterproofing composition, e.g., asphalt. This asphalt desirably is a skabilized material, which can be obtained by combining a mineral stabilizer with the aforementioned asphalt used to coat the base sheet's underside. Preferably, the asphalt coated upper surf~ce is also covered with a protective material to prevent blocking and sticking. This protective material may be a pervious or impervious covering such as that applied over the asphalt on the base sheet's underside.
The torchable base sheet of the invention can be produced by applying a coating of liquefiable asphalt on the underside of the support, which preferably is a continuous sheet, with a suitable device, e.g., hy roller ~oating, and thereafter contacting the coated surface with a protective covering, e.g., by bringing the coated surface into face to face contact with a plastic film. When the top side of the support is a fibrous surface, the process desirably includes the coating of this side with a waterproofing composition, sllch as asphalt, and the covering oE this wa~erproofing composition with a protective material. The manufacture of the torchable base sheet is preferably carried out continuously.
In a preferred method o~ manufacture, the base sheet support te.g., fiberglass mat) is impregnated and surface-coated on top with a stabilized asphalt containing approximately 30 - 60 wt % filler, which is surfaced with a fine mineral material, such as talc and/or sand. An unstabilized asphalt coating is applied at a suitably heavy covelage for ease of torching, e.g., 10-15 lbs./100 ft~J to B 1304 ~r~EMT
03/23/~0 5 the back sid~ of the lmpregnated mat, which ls surfaced with plastic film (e.g., light gau~e polypropylene film).
DESCRIPTION OF THE DRAWINGS
Th~ invention will now be described with r~fe~ence to the accompanying drawings in which:
FIG. 1 is a diagrammatic side elevational view of the ~rocess of forming the torchable roofing base sheet in accordance with the present invention; and FIG. 2 is a perspective view illustrating the application of the roofing base sheet of the invention.
DETAILED DESCRIPTION OF THE INVENTION
Referring to FIG. 1 of the drawings, the base sheet of the invention comprises a ~elt 11 preferably formed of a web of non-woven fibers which are stable and capable of lasting in the application and enviro~ment of the sheet. Glass fibers, or other similar fibers, formed into a web (e.g., a fiberglass mat), are suitable for this purpose. The glass mats of the invention may be manufactured in a conventional manner on conventional equipment such as single cylinder or Fourdrinier type machines.
Glass fibers are present in the base sheet of the invention in amounts o~ between about 70 and a~out 90 wt %
on a dry basis and preferably in amounts between about 72 and about 86 wt % on the same basis. Chopped glass fiber is especially preferred. The glass fibers typically have a ratio of length to diameter which is equal to 10 or higher, with lengths which vary between 0.1 and 100 mm, more typically between 1 and 10 mm and diameters~within the range of 0.1 to 25 microns.
Mat thickness may vary widely depending upon the desired end use requirement, with typical thicknesses between about 20 and 60 mils, preferably between about 25 and 35 mils. The mat is generally about 30 to 50 in wide, and generally weighs from about 1.40 to 2.20 lbs./100 ft2, ~referably from about 1.75 to 2.00 lbs./100 ft2.
Binder is used in mat 11 in amounts between about 10 and 30 wt %, based on total dry weight of the mat, with amounts of betwe~n about 14 and 28 wt %, on the same basis, B 1304 ~T~NT

~ ~ w ~ r~
being preferred. Any suitable binder known by those skilled in the art can be used. Typical mat binders include acrylamides, starch, urea resins, phenol resins, sodium silicates, epoxy resins, SBR, acrylics, neoprene, acrylonltrile or other natural or synthetic latices.
Preferred billders are acrylics, phenol-formaldehyde and urea~formaldehyde resins. After curing of the binder, the mat is wound up onto rolls for use.
The glass mat 11 may be coated on all or part of one or hoth faces thereof with asphalt or other such bituminous substances to provide the torchable base sheet of the invention. The terms "asphalt" and "bltuminous" are used in this specification and appended claims to define compositions formed from a bitumen, asphalt, tar or pitch base. Asphalt must be present on the underside of the mat ~or bonding to a roof substrate in accordance with the present invention. Blown asphalt is advantageously used to coat the mat. Although a major advantage of the present invention is that a low cost coating grade asphalt can be used to coat sheet 11, more expensive polymer modified asphalt may also be used. Fillers and other conventional asphalt additives may be included in the coatings.
A preferred method for ma~ing the improved base sheet in accordance with the invention is described in FIG. 1.
Fibrous mat 11 is unwound from a roll (not shown) and directed along a conveyor line toward the nip of rotating rolls 12 and 13. Prior to rolls 12, 13, discharge pipe 14 applies an asphalt coatin~ 15, which preferably is stabilized, to the top surface of the mat just be~ore the nip of rotating rolls 12, 13. Reservoir 16 is placed below the coating area to capture run-over asphalt from the operation for application by roll 13 -immersed in the asphalt of reservoir 16 - to the mat. Nip rolls 12, 13 coact to apply the appropriate weight of the asphalt coating to the mat, with the nip of the rolls providing pressure to ensure that the asphalt has impregnated the glass mat properly.

r, 1304 PATENT

~ ;3 ~ 'J~' Asphaltic coating 15 suitably has softenin~ point characteristics and a mineral Eiller content which contribute to a desirable degree of ~ire protection for the total roofing system. The mineral filler content of the coating should be high enough to impart excellent resistancc to flow and good resistance to indentation at normal roof temperatures during application, but low enough to make production of the base sheet practical. Stabilized asphaltic coatiny 15 suitably has a softening point as measured by ASTM D 36 of from about 200 to 250~F, more preferabl.y from about 210~ to 230F, and contains from about 30 to 60 wt %, more preferably from about 40 to 50 wt ~, mineral stabili~er, based on the total weiyht of the stabilized coatin~, as determined by UL 55B mineral stabilizer test. The mineral stabilizer is appropri.ately of the type commonly used in filled asphaltic coatings and may be derived from limestone, stone dust, sand and other sources of suitable fine mineral aggregate. Advantageously, the viscosity of filled or stabilized coating 15, measured at 35~F with a Brookfield viscometer, is in the range of about 500 to 2,000 cps.
Filled asphalt coating 15 is usually applied in an amount from about 5 to 40 pounds, more preferably from about 10 to 30 pounds, per 100 square feet o surface area of mat 11. This coating is advantageously maintained at about 325 to 3750F before application to the mat.
Rolls 12, 13 advantageously both impregnate the mat and surface coat it on the top side with the stabilized coating.
After the coated mat passes through the nip of rotating rolls 12 and 13, a scraper 17 is so located as to take coating 15 off the mat's bottom surface. The removed coating ls discharged into reservoir 16 for reapplication to the mat by roll 13.
The removal cleans the back surface for application of torchable asphalt, which is preferably unstabilized. The back side (roof deck side) of mat 11 must be coated with a sufficient quantity of asphalt that will not~ impede the normal production of the base sheet, but will, when heated B 1304 ~ATENT
~/23/90 ~ ~ ~ s~3 ~

~ith a torch (typically fired with LP gas) during application on a roo~ substrate, flow satisfactarily to laminate the base sheet to the substrate. For this purpose, this coating desirably has a softening polnt as measurèd by ASTM D 36 of from about 175~ to 225~, mGre preferably from about 190 to 2.10F, and a penetration as measured by ASTM D
5 of from about 10 to 30 dmm, more preferably from about 15 to 25 dmm. Its viscosity, measured at 375~ w.i.th a ~rookfield viscometer, is in the range of about 125 to 225 cps .
As is illustrated in FIG. 1, a hold down idler l8, which is heated by gas flame rod 19, smooths coating 15 on the upper surface of the mat before application of asphaltic coating to the back side of the mat. Asphalt coating 20, which is supplied to a reservoir 21 or the like cont.ainer by nozzle 22, may be an unfilled blown coating derived from an asphalt flux oil. A coating roll 23 is immersed in the supply of unstabilized asphalt contained in reservoir 21.
The roll 23, operating in the directlon indicated by the arrow, picks up the asphalt and applies it to the underside of the mat 11 being treated. Excess asphalt may advantageously be wiped from the surface of roll 23 by a doctor knife 24 or the like scraper to ensure uniform application and avoid excesses of the asphalt. A roll 25 located after application roll 23 smooths the back coating.
The temperature of the unstabilized back coating in application pan 21 is desirably from about 350 to 38SF.
Coating 20 is typically applied to mat 11 at a coverage of about 10 to 25 pounds, more preferably of about 10 to 15 pounds, per 100 square feet of surface area of the mat.
Cont.rolled asphalt coverage of the mat is also attainable through direct roll coating. The extent o~ coverage also may be af~ected by variables such as roll speed, viscosity of asphalt, etc.
Surfacing material is applied uniformly on the top asphalt layer 15 by a hopper 26 or other suitable device commonly used to apply inorganic surfacing to roofing products. This surfacing prevents blocking and sticking B 1304 PA~NT
n3/23/90 ~ ~3~ 3 ~

~uring subsequent processing and handling of the base sheet.
A fine mineral surfacing materlal, such as sand, talc or a mixture thereof(e.g., a 65:35 talc/sand mixture), can be app].ied or thls purpose. The mineral particles are typically applied to the surface of asphalt layer lS at a coverage of from about 2 to 6 pounds, more preferably about 1 to 5 polmds, per 100 Et2 of surf~ce area.
As the asphalt coated base sheet is conveyed around roll 27, a protective sheet or film 28, which is unwound from roll 29, is brought into contact with asphalt layer ~0 to form a covering on the layer. The film typically is about 37-38 in. wide. While film 28 is still on roll 29 and just before it is unwound therefrom, watex is sprayed lightly by nozzle 30 over the film to minimize ~ilm shrinkage. Typically~ the film is sprayed at an appropriate angle with a fine water mist, such as that from a Spraying System's nozzle. Tension put on roll 29 keeps the film sufficiently taut to minimize air entrapment between the film and hot asphalt.
Sheet 28 is preferably a plastic film (e.y., a polyolefin), which becomes united with layer 20 by virtue of the tackiness of the asphalt. Sheet 28 is substantially coextensive and congruent with layer 20. In a preferred embodiment of the invention, sheet 28 is a heat-stabilized, bi-axially oriented polypropylene film whose coverage thickness is from about 0.2 to 0.8 mil, more specifically, 0.3 to 0.6 mil (gauge). The moisture barrier properties and low shrlnkage of this film at high temperatures make it highly suitable for use on the torchable base sheet of the invention. The film serves as an anti-blocking agent in the finished roll of the base sheet, and readily melts when the finished product is torch-applied in place.
After film 28 has been deposited on the base sheet, the sheet is brought into contact with several cooling rolls 31 and thereby is cooled, and the coating asphalt solidifies gradually to form torchable base sheet 10. ~YFinally, the roofing base sheet is wound dry in the form of a roll, which is typically a one to two s~uare roll.

B 1304 P~TEN~

The torchable base sheet of the present invention may be simply and easily applied to a roof deck without the need for any ho-t-mopped bitumen for bonding the sheet to its underlying substrate. The underlying roof substrate may include precast or poured concrete decks; insulated roof decks; cellular or non-foam roof insulation applied over various roof decks, such as wood, plywood, steel, other existing roofs, and the like; and coated base sheets or roofing felts applled over nailable roof decks, such as tongue and groove, shiplap or splined wood, plywood, gypsum or structural wood fiber decks. In the case o-E porous uppex deck surfaces, such as concrete decks, it is sometimes desirable to prime the surface to promote good adhesion before applying the torchable sheet of the invention.
Application of the torchable base sheet to a roof surface is simply accomplished by heating the asphalt coating on the underside of the sheet with a roofing torch or the like to melt the asphalt which then becomes adhered to the surface when the coated underside is brought into contact with the surface, and allowed to cool. The aIIti-blocking plastic film also fuses when torched during application.
FIG. 2 illustrates the application of asphalt-coated base sheets of the invention over an existing built-up roof.
The surface to be covered should be dry, smooth, and free of debris or loose materials which might inhibit adhesion of the torchable base sheet. After the surface has been thus prepared, it can be suitably primed with a conventional asphalt primer. Starting at the low point of the roof, the first roll or strip 32 of torchable base sheet is positioned with the plastic (e.g., polyolefin) film side down on the roof surface 33 to be covered. A conventional propane-fired hand torch 34 is used to apply heat to the underside of the roll.
The base sheet is desirably applied with two rows of spot torchings. For example, in the case of a 36 in. wide roll, heat is applied to the plastic side of the roll on an area approximately 12 inches in diameter and centered about B 130~ PATE~T
~/23/90 11 ~ 7 ~ inches i,n from the edge of the roll. When the asphalt on the heated area has softened sufficiently to become molten, the roll is moved forward until the melted asphalt comes in contact with the surface to be covered, bonding the roll in place. The softening process is repeated with the torch directed to the opposite side of the roll. The two rows o-f spot torchings are thereby staggered, w,ith the spot torchings in each row appropriately being about 12 inches in diameter and 24 inches on center.
The second and succeeding rolls are installed in the same manner, alternately applying heat to one and then the other side of each roll, with the ends of each succeeding roll being lapped a 3 inch minimum seam 35 over each preceding roll in the same course. The same procedure is Eollowed for the second and succeeding courses, with the rolls of base sheet being applied with a lapped seam 36 over the upper edge of each preceding course to form a nominal 2 inch side lap.
~ cap sheet, which may be smooth or granule surfaced, is suitably applied (e.g., by torching) over the base sheet to complete the rexoofed system of the invention. Typical modified bitumen membranes for application over the base sheet are Celotex~ APP Smooth Surface and SBS Mineral Surface Cap Sheets, available from The Celotex Corporation, Tampa, Florida. The exposed surface of the cap sheet may be surfaced with a conventional roo~ coating to provide a protective ~uter layer.
The present invention provides a unique asphalt-coated roofing membrane base sheet which can be torch applied to either new or existing roof decks, eliminating the need to mop hot asphalt or mechanically fasten the membran~. The parti,cular expense and difficulty associated with the use of hot-mopped asphalt are thus avoided. The torchable base sheet can be spot torched, thereby providin~, venting paths for the escape of moisture from its lmderside. This method of application is especially suitable in rerooflng over an existing roof. Either the spot torching application of the base sheet or mechanically fastening it provides for relie~

1~04 PATF.N~
~3/~3/90 12 2 ~ 3 ~f~ 7~
oE pressure through lateral vapor movement, thus minimizing bllstering potential between the substrate and the new roof membrane. When the base sheet is mechanically fastened, the plastic film also contributes to the vapor-retardant properties of the sheet. The base sheet can also be completely torched to the substrate, e.g., ln new ~onstruction.
The base sheet can be coated with unfilled or filled relatively low ~ost asphalt, as opposed to more expensive polymer modified asphalts, which further require specialized processing equipment. In accordance with the present invention, coating asphalt conventionally used in the roofing industry may be used and applied without any major expense for specialized equipment.
The asphalt-coated iberglass base sheet of the invention has excellent built-in torching capability and provides a uniform adhesive bond. It can be easily and quickly applied to a roof surface in less time than is required to apply a conventional fiberglass base sheet by spot-mopping with hot asphalt. The torchable low cost asphalt on the underside of the sheet melts ~uicker when exposed to torch application than do most polymer modified products and this results in a faster application rate.
When the torchable base sheet is applied over certain insulation products, there is less danger of fire as compared to the application of hot molten asphalt.
Additionally, the sheet possesses higher tensile strength, tear and nail pull through resistance than the conventional ~iberglass ~ase sheets, and remains pliable at temperatures of ~25F and above. The base sheet's properties exceed the detailed re~uirements outlined in ASTM D 4601 and ex~eed the U.~. Type G2 requirements for fiberglass base sheets.
The invention is further illustrated by the following example.
EXAMPLE
A roofing base sheet of the invention was prepared in the following manner.

B 1304 ~AI'EN'r ~ ~3~.~37 Using the appaxatus shown in FIG. 1, a ylass mat o:E
1.78 lbs./100 ft7 was passed under nozzle l5 which deposited f.illed molten blown asphalt 15 heated to a temperature of 350F and having a softening point (ASTM D 36) of 220F.
Stabilized c3a-ting 15 contained approximately 45% of a limestone filler, based on the total weight of the fi.lled asphalt. A~ter asphalt application by rotating rolls 12, 13 and the removal of asphalt from the mat's underside by scraper 17, the underside was coated by roll 23 with the same blown asphalt as above except that the asphalt was unfi.lled, and had a softening point ~ASTM D 36) of 200F and a penetration value (ASTM D 5) at 77F oE 20 dmm.
Unstab.ilized asphalt 20 was heated to a temperature of 380F.
Sand surfacing was applied from hoppex 26 to the advancing base sheet to form a top surfacing on asphalt coating 15 with a coverage of 2-6 lbs./100 sq.ft. A 0.4 mil thick polypropylene release ilm was applied at roll 27 as back surfacing material for the base sheet. The surfaced asphalt-coated base sheet (torchable base sheet) was cooled by a series of rolls 31 and wound up into rolls.
The following Tables I and II show the composition and physical properties, respectively, of a typical torchable base sheet produced in accordance with the inventi.on.

B 1304 P~TENT
03l~3/90 1~
~ ~3 3 ~
TABLF I

COMPOSITION

Ingredient T.. bs. per 100 sq. It .

Glass Mat 1.8 Stabilized Coating Impregnant 10.0 Top Surface 10.5 Fine Sand (top) 4.5 Unstabilized Coating (back) 13.3 Polypropylene Film (back) 0.2 Net Weight 40.0 Filler Content in Stabilized Coating, % weight 45 2 ~ 3 ~
TABLE II
TORCHABLE BASE SHEET
PHYSICAL PROPERTIES

Roll Weight, lbs./1.5 Sq. Roll 60-70 Average Wt, lbs./CSF 35-45 Average Thickness, mils 70-80 Average Tensile 5trength, MD 60 90 lbf/in @ 75F CD 50-80 Average Elmendorf Tear Resistance, MD 500-1000 @ 75F, gm CD 500-1000 Pliability over 1" diameter Mandrel, No @ 75F, 35F, 15F Cracking

Claims (21)

1. A roofing base sheet for application by use of heat to an underlying substrate comprising:
(a) a sheet of a flexible material, (b) a layer of a first asphalt composition covering the underside of the sheet, the asphalt composition being liquefiable by the use of heat for application and adherence to the underlying substrate, and (c) a protective covering over the firs-t asphalt composition to prevent its sticking, the protective covering being a pervious material or an impervious material convertible by heat to a pervious condition so that heat applied to the underside of the sheet liquefies the asphalt composition and renders any impervious covering pervious, whereby the liquefied asphalt composition can be directly applied to the underlying substrate.

2. The base sheet of claim 1 wherein the sheet comprises a woven or non-woven fabric made of synthetic or natural fibers.

3. The base sheet of claim 2 wherein the fabric comprises a fiberglass mat.

4. The base sheet of claim 1 wherein the first asphalt composition has a softening point of from about 175°
to 225°F.

5. The base sheet of claim 1 wherein the first asphalt composition comprises a polymer modified asphalt.

6. The base sheet of claim 1 wherein the protective covering over the first asphalt composition comprises a plastic film.

7. The base sheet of claim 6 wherein the plastic film is polypropylene.

8. The base sheet of claim 1 wherein the top side of the sheet is covered by a waterproofing composition.

9. The base sheet of claim 8 wherein the waterproofing composition comprises a second asphalt composition having a softening point of from about 200° to 250°F and containing a mineral stabilizer.

10. The base sheet of claim 9 wherein mineral particles are applied to the surface of the second asphalt composition.

11. The base sheet of claim 9 wherein the second asphalt composition contains from about 30 to 60 wt % of the mineral stabilizer.

12. The base sheet of claim 1 wherein (a) the sheet comprises a fiberglass mat, (b) the layer of the first asphalt composition has a softening point of from about 175° to 225°F, and (c) the protective covering over the first asphalt composition comprises a plastic film.

13. The base sheet of claim 12 wherein a filled second asphalt composition impregnates the fiberglass mat and forms a layer on the top side of the mat.

14. The base sheet of claim 13 wherein the layer of the filled second asphalt composition has a softening point of from about 200° to 250°F, and is surfaced with mineral particles.

15. The base sheet of claim 14 wherein (a) the fiberglass mat weighs from about 1.40 to 2.20 lbs./100 ft2, (b) the layer of the first asphalt composition on the underside of the mat weighs from about 10 to 25 lbs./100 ft2 of surface area of the mat, and (c) the layer of the second asphalt composition on the top side of the mat weighs from about 5 to 40 lbs./100 ft2 of surface area of the mat, and contains from about 30 to 60 wt % of a mineral stabilizer.

16. The base sheet of claim 15 wherein (a) the mineral particles surfacing the layer of the second asphalt composition are selected from the group consisting of sand, talc and mixtures thereof, and are applied at a coverage of from about 2 to 6 lbs./100 ft2 of surface area of the layer, and (b) the plastic film surfacing the layer of the first asphalt composition is polypropylene.

17. A method for producing a roofing base sheet suitable for application by use of heat to an underlying substrate, which comprises the steps of:
(a) applying an asphalt composition to the underside of a sheet of a flexible material, the asphalt composition being liquefiable by the use of heat for application and adherence to the underlying substrate, and (b) applying a protective covering over the asphalt composition to prevent its sticking, the protective covering being a pervious material or an impervious material convertible by heat to a pervious condition so that heat applied to the underside of the sheet liquefies the asphalt composition and renders any impervious covering pervious, whereby the liquefied asphalt composition can be directly applied to the underlying substrate.

18. A method for producing a roofing base sheet suitable for application by use of heat to an underlying substrate, which comprises the steps of:
(a) applying a filled asphalt composition to a sheet of a flexible material to impregnate the sheet and form a layer on the top side and a layer on the underside of the sheet, (b) scraping the filled asphalt composition from the underside of the sheet, (c) applying an unfilled asphalt composition to the underside of the sheet, the unfilled asphalt composition being liquefiable by the use of heat for application and adherence to the underlying substrate, (d) applying a mineral material to the surface of the filled asphalt composition to prevent its sticking, and (e) applying a protective covering over the unfilled asphalt composition to prevent its sticking, the protective covering being a pervious material or an impervious material convertible by heat to a pervious condition so that heat applied to the underside of the sheet liquefies the unfilled asphalt composition and renders any impervious covering pervious, whereby the liquefied unfilled asphalt composition can be directly applied to the underlying substrate.

19. A method of covering a roof substrate comprising the steps of:
(a) placing on the roof substrate the roofing base sheet of claim 1, (b) heating the underside of the base sheet to liquefy the first asphalt composition and render any impervious covering pervious, (c) bringing the liquefied first asphalt composition into contact with the roof substrate, and (d) allowing the first asphalt composition to solidify, thereby adhering the base sheet to the underlying roof substrate.

20. The method of claim 19 wherein a conventional cap sheet is applied over the roofing base sheet.

21. A roof assembly comprising:
(a) an underlying roof substrate;
(b) the roofing base sheet of claim 1 disposed over the roof substrate; and (c) a conventional cap sheet disposed over the roofing base sheet.