US2296553A - Liner for cement and concrete forms - Google Patents

Description

sept.. 22, 1942.

C. C. HERITAGE ETAL LINER FOR- CEMENT AND CONCRETE FORMS .Filed May 2, 1940 Patented Sept. 22, 1942 LINER FOR CEMENTAND CONCRETE FORMS Clark C. Heritage, Cloquet, Minn., and W. Bartlett Jones, Chicago, Ill., assignors to Wood Conversion Company, Cloquet, Minn., a corporation of Delaware Application May 2, 1940, Serial No. 332,984

18 Claims.

there is no severe bonding of the form to concrete. .It has become known that if a hydraulic mix has less Water than that required to pour it,

to handle it, and to assure uniform mixture, the

concrete which results is harder and of better quality. It has therefore beenproposed to use absorptive material as a liner for concrete forms, whereby the excess water of the mix, required for uidity and present at the form face, is taken out at the immediate surface lying against the the set concrete.

Among the absorptive materials proposed for such action is fiber board, such ascommon insulating board, made of ligne-cellulose fibers, such as wood, cane, cornstalks, and the like. One of the diiculties encountered in the use of such boardis the adequate control of absorption of mold with a resulting case-hardening" effect on of a moisture-retaining liner to aid in setting the cement or concrete.

A particular object is to provide a form liner which has a sealing coat on the mold face whereby loss of water from the board is minimized.

Various other and ancillary objects and advantages of the invention will be apparent from the following description and explanation and from the accompanying drawing in which:

Fig. 1 represents a fragment of a concrete form adjacent a wet mix as they are immediately placed in contact and before any functions have been exercised.

Fig. 2 represents the `same structure of Fig. 1 after the desired action has taken place.

Fig. 3 is an ed'gewise view of a modied form liner, showing in particular a sealing layer on the mold side of the liner.

One of the first endeavors in avoidance of bnding was theprovision of a coating on the board. Numerous coating materials were found to be successful to prevent bonding, but these water, the release of air in bubbles at the form surface, and a bonding of the board to the set concrete. The present invention aims to overcome these and other difliculties. It is an object of the present invention to provide an improved method and means for molding cement, concrete and the like, which is effective f to case-harden the set surface in a manner to avoid pits therein, while at the same time to avoid adherence of the surface to a mold surface.

A particular object of the invention is to provide a porous surfaced form-liner as a board having a coating thereon to permit stripping while attaining the major objectives of the invention.

A further object of the invention is to provide a' wetting agent for the water of the mix upon contact with the form liner.

A particular object of the .invention is to provide a wetting agent in the coating of the form liner.

Still another object of the invention is to provide a form liner of limited absorption characteristics whereby the liner provides af thermal insulating effect.

Another object of the invention is the provision introduced other difficulties. It was found that coatings which successfully insulate the fibers from the concrete, so changed the surface of the board that the penetration by water could be prevented or permitted and controlled. To permit penetration, it was found that the coatmust be s uiliciently incomplete to leave pores intovvthe board, yet sufciently complete to avoid bonding. This could readily be accomplished (see Heritage Serial No. 326,543, led March 29, 1940) but other difficulties were introduced.'

One of the advantages of using some ordinary uncoated fiber boards was found to be the release of air entrapped orpresent in the concrete mix.

Air forms bubbles which tend to rise in the con-` crete where it is fluid. The setting and the de- "hydrating of the mix are two causes for loss of plasticity, To avoid air pockets the air must be removed before a non-plastic stage is reached. Air bubbles at mold 'surfaces cause undesirable pits. A highly porous fiber board on one hand tends to lessen pitting by permitting escape of air, but on the other hand it tends to effect pitting by more quickly dehydrating the mix to a non-plastic state.

One effect of coating aboard to leave open pores is to decrease the absorptiveness of the board. Control of the coating therefore permits control of the rate `of .absorption through the surface, neglecting' the capacity of the interior fibers, and assuming that to beconstant. Such control appears to prolong the plastic stage, so

that less pitting might be expected. However,

and'as a matter of fact, absorption-limiting and non-bonding coatings have increased the tendency to pit, over the use f uncoatedboard.

It was found that a non-bonding coated board having open surface pores and giving satisfactory performance in the lower parts of the mold, showed near the top of the mold and above a more or less welldefined line, numerous pits or air pockets in the set concrete after removal of the board. A great deal of diflculty has been encountered not only in explaining this, but in overcoming it. Fro'm the solution of the problem, there appears now to'be a reasonable explanation which supports the solution. One of the baffling angles was the fact that the same coated board was successful or unsuccessful according to its position in the mold. The only obvious difference.

in conditions might seem to be in the hydraulic head `effective to force water through the pores of the board. 'However, because the top pitted portion vis substantially as well case-hardened as the non-pitted lower portion, the answer seemed not to lie in hydraulic head.

Numerous experiments wherein non-bonding coated board was used giving the said top pitting without pitting below. showed that the board was suitable for bottom conditions, but not for top conditions- Knowing that inferior surfacetreated boards give pitting at the lower regions;

it follows-that the air which produces this vhas in successful regions escaped through the board while the mix was sufficiently plastic to ll the air space. By numerous experiments it has beenv determined that by increasing the wettability of the surface by adding wetting agent-s to the tested coating composition, the avoidance of pittingl was made complete.

This has led to an acceptable explanation. Bubbles of air which are positioned to form surfacepits have a surface tension of the liquid definingthem. The air pressure in the deeper bubbles is greater than in the bubbles above them. The air in the board is at atmospheric pressure, due to its appreciable porosity. Upon contact of a bubble which is of size clearly visible to the eye, with a pore-opening in the board, which is not visible to the eye, the tension of the film of the bubble acts as a skin or diaphragm across the pore or pores tending to prevent the air in the bubble passing through the porous surface of the board. The skin is a boundary between the air at the higher pressure in the bubble and the air at atmospheric pressure in the board. Where the differential pressure is sufcient to rupture the skin, the air may pa'ss through the pore If this happens while plastic mix surrounds the bubble the mixmoves in to close what would be a pit, if the mix'were dehydrated or set to a nonplastic mass before escape of the air. At the top of the mold, Where pits occur, it appears that the cement has become non-plastic before the bubbles break. With the same board and surface, and the same mix, it follows that the pressure in the bubble at the top is not sufficient to break the skin while the cement is plastic. e

Wetting agents are well known to lower surface tension, so that such bubbles" would break leasier or at lower differential pressure if wetting agent may reach the film. Water soluble material in the board or coating is available-t0 diffuse to the-bubble-'skin to alter its surface Since the boards tested, which gave"v satisfactory performance at the bottom of the tension.

mold, contained in the coating some water-soluble material, this may have had some .influence on the breaking of the bubble-skin together with y the differential pressure. At the pitting level this inuence,4if any, was not sufficient to overcome the lower differential pressure. By adding a pronounced wetting agent to the coating composition of this partially successful board, the' dehydrate the mix to render it non-plastic. Cou-, pled with this the hydraulic setting also tends to render the mix non-plastic. The vertical depth in the mass also has an effect in determin-` ing where a given degree of plasticity is effective to close4 a pore, and this is especially true where some dewatering has already occurred, whereby the inner portions are still fluid to exert hydraulic head on the less .Huid surface adjacent the mold.

While these transitions occur, the water entering the board sets up a liquid medium or channel for diffusive migration of water-soluble material. Assume a wetting agent in the board, and not in a coat over the board. An appreciable time interval will prevail for the wetting agent to diffuse through the coating layer to become effective on a bubble skin blocked by the coat. The mix may readily'be too dehydrated during this period to remain plastic sufciently long to close a bubble space, should the skin of the bubble reach the breaking point. Now, assume a wetting agent on or in the coat. It is `thus available to function promptly upon contact with the air bubble, to release the air through the pores and into the board.

There is also another effect which is to .be considered. The sizeof the pore determines the span over which the bubble skin is stretchedA as a barrier. 'Ihe smaller the Ipore the stronger the skin will resist breaking. Where the coating lagent swells the tendency is to make the pores smaller. Therefore, the very act of wetting the coat tends to lessen the ease of breaking the bubbles. The presence of wetting agent in the coat causes the coat to wet easier land therefore to swell quicker. But at the same time the wetting .agent breaks the bubbles promptly.

Protein and like hydrophilic coats swell rather slowly, and this is advantageous, since the mix may be dehydrated beforev swelling is complete, and then the pores are wholly or partially closed by the later swelling. With half inch rboards of a -waxed-sized fiber, used for slight waterproofing effect, it has been observed that the board is wetted for a depth of about 1/8 to 1A inch, leaving a dry layer of the remainder. This provides insulation against heat and cold, and a barrier to evaporation of water from the wetted portion of the board. Since it is desirable to prevent early drying of setting cement mixtures, this situation is highly advantageous to the setting action producing high strength, in addition to high density from the case-hardening effect.

v'he .effectiveness of such action may be increased by providing a sealing coat for the back of the board, and preferably a sealing coat which is a -moisture barrier, such as an asphalt layer. A high melting point asphalt (288 C. melting point) such as one-Which will not become tacky .at F. is very desirable. Such boards in hot sunny climates, or in forms exposed to heating from the sun, may be used with no bad effect from tackiness of a coating. Boards coated with such asphalt have been made which are not tacky until at a temperature of about 170 F.

Mention is made above of a ber board made of bers with a water-proofing size. Such a board without a coating on one surface is wetted in a standard test only after 8 hours. But the same board with a protein coat on the other side is wetted in the same test in 15 seconds, and then when wetted the water continues to wet the board inwardlyl It is Ibelieved that the capillary spaces between the sized water-resisting fibers, rather than the fibers per se, are the means permitting the board to dehydrate the mix, after the water gains early entrance quickly because of the coated surface. It is also believed that the sizing of the fibers is a means to control the depth to which the board is wet, giving the insulating value to the unwetted part.

The wetting time as above indicated may vary widely. Where it has been found to be 15 seconds for the type of coated board particularly described herein, successful .non-.pitted surfaces have been obtained. Where it has been 30 seconds, slightly imperfect surfaces have been obtained. Where a few small pits may be tolerated the wetting time may be as high as 4 minutes. It also appears that rapid absorption is conducive to removing too much water too fast' before the actively moving mass, while being poured, can settle to a stable hydraulicmass. The coat on a highly porous board appears to act as a barrier to substantially instantaneous absorption, lfor only a matter of seconds, while the mass becomes stabilized in the mold.

In practice, the ,preferred board is one-half .inch thick and made of vegetable ber at about 16 pounds per cu. ft. density (dry weight) with about to 12 pounds of sizing wax to 1000 sq. ft. of board. This wax in emulsion form in the slurry of stock from which the board is made is precipitated by alum to deposit wax on the fibers. On heating the board in the drying operation, the wax is melted to effect the completion of fiber sizing. Y

'Ihe wet-board forming stock is coated with a viscous dispersion of the hydrophilic coating base. The wet stock minimizes penetration of the disperson into the board, keeping it well at the surface. The drying of the so-coated wet mat simultaneously dries the coat and the board from its two sides. The usage of coating dispersion is such that on shrinkage Vin drying, the surface fibers are wholly or partially coated, with the -important result that .openings are left to the interior of the board. The extent of partial coating is determined by the permitted degree of bonding. Complete coating, however, is preferred. y

The coat material should be one which is hydrophilic and relatively insoluble or non-remov- 4 able under conditions of use. Where it houses the fwetting agent, the coat' should be water absorbent so that the wetting agent is available to exercise its function upon contact with water. Where' the coat. material imbibesy water and swells, it should be so applied asto avoid closing of the Ipores .by swelling. From the nature of kfilm-coats lacking pigment.

pigment coats, there is a transfer of pigment to gelatin, and like gelatinous film-'forming hydrophilic colloids.

Protein coats containing pigments, in the form of pigments dispersed in a film of the coating base, or in the form of pigments bound together and to the fibers by protein, have been successful, but they are not as satisfactory as In protein-bonded -the surface of the concrete, which may not be desired, since it is not.permanent. Also, the protein-bonded pigment coats have less tendency to swell, owing to the lower content of the protein. Best results have been obtained with a hydrophilic film coating lacking pigments.

In the drawing the numerals I0 and 'II represent parts of a suitable concrete form of a normal construction, wherein it is common to pour the mix directly against the form boards II. Numeral I2 represents a wet concrete mix, and the bodies designated I3 are representative of aggregate therein. The small circles I4 are indicative of air bubbles, and are not intended to designate size, or uniformity of size or position or fixation of position. It is only intended to indicate that near the surface there is air in the mix which is capable of forming pits of various sizes in the surface.

The numeral I5 in Fig. l represents a board of fiber as above described, having a coating thereon which is porous, as above described. The broken heavy line I6 is diagrammatically illustrative of a porous coating on the surface, and

the action as it appears to be .presently understood, it appears most favorable to have a coat which does wet and swell, but which does not seal the pores on swelling.

Coatings which appear to be satisfactory are proteins, such as soya bean protein, casein., corn protein, chromated or other insolublzed glue or itis not intended to indicate that it is as uniform as in the diagram. In general it is to be understood that it may be coatings on individual bers, which coatings'join at ber contacts and crossings, leaving pores or openings of various shapes and sizes.

In Fig. 2, the unchanged parts are designated by the same numerals as are usedin Fig. l. Thus, for example, a part of the board I5 remains unchanged, and the aggregate I3 remains unchanged. The heavy-lined part of the board is designated 20, and represents board I5 `with water therein. The thickness of zone 20 may be less, or greater, and may be the entire thickness of the board. The coating line is shown as 2|, and represents the coating I6 after it has been wetted. The matrix I2 of Fig. 1 appears in Fig. 2 as set mix` 22 of normal density such as is produced by the hydraulic setting of matrix I2. The heavier part 23 indicates the case-hardened surface resulting from water'of matrix I2 moving into the board wherein it appears in region 26. The thickness of zone 2l maybe less or greater than shown, and does no t represent any precise' ratioto any other dimension in-Fig. 2.

It is shown in Fig. 2 that there are no air bubbles, these having been destroyed bythe desired functioning, resulting from the effects of wetting, agent available from the board, las in coating I6 of Fig.' l.

In Fig. 3,v a fiber board 25 has a coating 26 which is of the type described, and its porosity i is' indicated in t-he diagrammatic manner with roughening treatment.

The board of Fig. 3, may be used as asubstitute for the board l5 in Fig. 1. v The following illustrates the preferred embodiment of the invention. Wood ber, which may be any hydrated board-formingv stock is made into a board, preferably of about 1/2 inch thickness, weighing about 16 pounds per cu. it. The process as set forth in Frost U. S. Patent No. 2,154,201 is used, with or without the surface For smooth concrete surfaces 4the roughening treatment is omitted. In this process the ber slurry may or may not be treated bya sizing composition to lessen the absorbency of the bers. Where it is so treated the amount of .coating composition needed for the desired eect is materially reduced. For example, where the bers are sized with about 11 pounds of wax or a mixture of waxes per 1000 sq. f t. of board, precipitated from emulsion form in the presence of the bers by adding aluminum sulfate as precipitant, the amount of the coating composition given below is cui in half, for the desired effects.

The coating composition is a viscous stable liquid which 'is applied from a pool behind a 'roll pressing on the wet board-forming mat before it enters the drier, whereby the board and the coat are driedjtogether. The fact that the tlbers, sized or un'sized, are wet, limits penetration of the coating composition into the mat, and further gives a'lower usage.

A suitable coating composition is as follows:

' Parts by weight Water 2,160 to 3,356 Borax 17 Boric acid 10 Protein (soya bean) (7-8% water)- 100 Glycerin 10 Sodium sulfonate of lauryl alcohol (dry basis) to 55 The protein is dissolved in the water with the borax to provide alkalinity for dispersing it. The boric acid and glycerin are added to reduce the pH to just below the neutral point, whereby the coating is less likelyY to be redispersed if accidentally wet with waterf The glycerin tempers the coat to prevent'it chipping. Part of the water of the formula may be included i in a paste form of the wetting agentgwhere such form is employed for economy.V Itis` available commercially as a 40% paste. The composition is used at a concentration of about 60 to 80 pounds (2.6 to 2.3 pounds of protein) per 1000 tity over a range which will vary with the nature of the mix of concrete to be treated, pertaining to the coating process and composition, and with variations in the board coated. The more protein added to permit stripping', the more wetting agent required in compensation. For example, in the use of materials of the above formula, a

non-bonding coat of 1.5 pounds of proteinper drocarbons, oils, and the higher aliphatic alcov hols, are the preferred wetting agents. y

Glycerin is a valuable element since it tempers the coat with a higher water content making it less brittle, owing to the hygroscopicity of gly'cerin. The glycols, mono, di, and tri-ethylene glycols, and other so-called glycerin substitutes are also useful in like manner, since they are non-reactive with the content of wet concrete.

The sulfonate wetting agents generally have high degree of wetting power and a minimum of other respect to the formula having the lower quantity of constituents, while the usage of 80 pounds is with respect to the formula having the higher quantity of constituents. TheseV respectively correspond to about 2.5 vpounds of the protein per 1000 sq. ft. As more water is used in the formula, the usage of the composition must be increased `to give the same protein deposition. Change of water content reversely changes viscosity. Lower viscosity causes deeper penetration, and calls for use of more wetting agent in compensation, The wetting agent may be varied in kind and quanei'fects requiring consideration in this invention.

In the preferred practice of the invention the board is coated in its unfinished form, when it is a. wet board-forming mat, and the coat and the mat are dried together. 'I'his practice minimizes the usage of composition, penetration into the board. In particular it minimizes the amount requirements of wetting agent, and concentrates it at the surface. Its absence at the interior of the board, especially of a sized-ber board, minimizes the penetration of water absorbed from the concrete, yielding a dry zone in the board for a thermal insulating function.

It is of course to be understood that the board may be made in many other ways, some of which are given but briey:

1. A dry ber board is coated with a composition containing both the hydrophilic base of the coat and the wetting agent.

2. A dry fiber 'board is coated with a composition containing the hydrophilic coat and lacking the wetting agent, and then on the wet or the dried coat Ia dust, paste or solution ofthe wetting agent is applied.

3. A dry fiber board is formed from a ber mass carrying also wetting agent, which on drying creeps to the surface. Such a board 'is coated with the coating composition lacking wetting agent. y

4. A wet fiber mat is formed from a fiber mass carrying also wetting agent, and the wet mat is coated with the coating composition lacking wetting agent. On drying both together, the wetting Iagent in the mat concentrates at a surface wetting agent Vmust be at, on, in, or very neart the surface so as to be available in quantity in time to function before the mix becomes unable to close the space of 'a pit.

Whenthe preferred board herein described.

sealing coat and under a given set of conditions,

,the case-hardening effect has been secured to a depth of about t/ inch. The same board, having an asphalt sealing coat, and used under the same conditions, has given a. case-hardening effect of about M4 inch. The depth of wetting of the. board was deeper in the asphalt-coated board. |I'his is believed to be due to a temperature effect. I'here is a heat of wetting when water is absorbed by the board, and there is a heat of setting for the hydraulic mix. Wateris more viscous as its temperature is lower. -Therefore, it is believed that the sealed board represses the dissipation of heat, especially by limiting the escape of water vapor, with the result that a slightly higher temperature prevails where the board is sealed. However, it is not intended to offer this as the full or proper explanation.

The board may be laminated to plywood or other sheet material, using adhesive such as asphalt or other substance to seal the board at the interface.

Although the invention is illustrated more particularly by reference to cement and concrete, it is applicable to' materials such as plaster of Paris, lime-base plaster-like mixes, aqueous ceramic masses, and the like. For example a claywater mix of sufficient uidity or plasticity to be cast in a mold, is one example. l A thixotropic mixture may be thin, and set without the necessity for a chemical change by hydration, which occurs with plaster of Paris and calcined cement masses; In general, the terxn hydraulic-setting masses includes all such mixtures, since they present the same problems and act in the saine way, with respectto use of the board herein described.

We claim:

1. A mold-form member for molding poured hydraulic-setting mixes of concrete and the like, comprising a Water-absorptive articial board of felted ber, a hydrophilic coat on said board discontinuous in extent and providing inter-connected coatings on surface bers with pores from the interior of theboard opening through the coated bers, said coat serving to prevent bonding of the bers to the set hydraulic material, and a wetting agent available at the surface of the board,V said agent being active upon contact with the poured mix to facilitate the rapid entry of entrapped air from the mix into said board through said coat.

2. A mold-form member for molding poured hydraulic-setting mixes of concrete and the like, comprising a. water-absorptive artificial board of felted ber, a hydrophilic coat on said board discontinuous in extent and Vproviding interconnected coatings on surface fibers with pores from the interior of the board opening through the coated bers, said coat serving' to prevent bonding of the bers to the set hydraulic material, and a wetting agent incorporated in said coat, said agent being active upon contact with the poured mixto facilitate the rapid entry of entrapped air from the mix into said board through said coat.

3. A mold-form member for molding poured hydraulic-setting mixes of concrete and the like, comprising a vegetable fiber artificial board having felted fibers and inter-ber spaces, a waterswelling coating" material on the surface bers able at the coated surface of the board, whereby wet concrete in contacting the coat of the board causes the coat to swell and be rapidly wetted for permitting rapid entry of entrapped air through the pores to the interior of the board.

4. A mold-form member forA molding poured hydraulic-setting mixes of concrete and the like, comprising a vegetable fiber artificial board having felted fibers and inter-fiber spaces, a waterswelling coating material on the surface fibers of said board interconnected as a discontinuous coat providing pores from the surface to the inof said board interconnected as a discontinuous coat providing pores'from the surface to the in-` terior ofthe board, and a wetting agent avail- 'terior of the board, and a wetting agent incorporated in said coating material, whereby wet 'cncrete in contacting the coat of the board causes the coat to swell and be rapidly wetted for permitting rapid entry of entrapped air through the pores to the interior of the board.

5. A mold-form member for molding poured hydraulic-setting mixes of concrete and the like, comprising a vegetable ber artificial board having felted fibers and inter-fiber spaces, -a waterswelling protein coat on the surface fibers of said board interconnected as a discontinuous coat providing pores from the surface to the interior of the board, and a wetting agent available at the coated surface of the board, whereby wet concrete in contacting the coat of the board causes the coat to swell and be rapidly wetted for permitting rapid ,entry of entrapped air through the pores to the interior of the board, 1

6. A mold-form member-for molding poured hydraulic-setting mixes vof concrete and th'e like, comprising a vegetable fiber artificial board having felted bers and inter-ber spaces, av waterswelling coating material on the surface bers of said board interconnected as a discontinuous coat providing pores from the surface to the interior of the board, and an organic sulfonate wetting agent available at the surface ofthe board whereby wet concrete in contacting the coat of the board causes the coat to swell and be rapidly wetted for permitting rapid entry of en trapped air through the pores to the interior of th'e board.

'7.'A mold-form member for molding poured hydraulic-setting mixes of concrete and the like, comprising a vegetable ber artificial board having felted fibers and inter-ber spaces, a waterswelling coating material on the surface bers of said board interconnected as a discontinuous coat providing pores from the surface to theinterior of the board, and a wetting agent included in the coat whereby wet concrete in contacting the coat of the board causes the coat to swell and be rapidly wetted for permitting rapid entry of entrapped air through the pores to the interior of th'e board.

8. A mold-form member for molding poured hydraulic-setting mixes of concrete and the like,

comprising a vegetable ber articial board havving felted bers and inter-fiberspaces, a waterswelling coating material on the surface bers of said board interconnected as a, discontinuous coat providing pores from the surface to the interior of the board, and an organic sulfonate wetting agent included in the coat, whereby wet concrete in contacting they coat of the board causes the coat to swell and be rapidly wetted for permitting rapid entry of entrapped air through the pores to the interior of th'e board.

`9. A mold-form member for molding poured hydraulic-setting mixes of concrete and the like,

comprising a vegetable ber artificial board hav--V ing felted ber and inter-fiber spaces, a soya bean protein as a lm coat on the surface iibers of saidboard interconnected as a discontinuous I lin which the fibers o f the board are sized with a. water-resisting size decreasing the absorbency of the fiber per se.

12. A mold-form member according to claim 8, in which the bers of the board are sized with a water-resisting size decreasing the absorbency of the fiber per se.

13. A mold-form member for molding poured hydraulic mixes of concrete and the like, comprising a felted iiber board having interfiber porosity, a water-resisting size on said fibers. a

. hydrophilic coat on said board discontinuous in extent and providing interconnected coatings on surface fibersA with lpores from theI interior of the board opening through the coated fibers, said coat serving to prevent bonding of the bers to the set hydraulic material, and a wetting agent available at the surface of the board, said 'agent being active upon contact withv the poured mix to facilitate the rapid entry of entrapped air into the board through said coat,"and said size on the `ibers limiting the entry of i-waterv into the board, whereby a portion remote from the mix may remain dry as an insulating layer.

14. A mold-form member according to claim 13 in which the face of the board opposite said hydrophilic coat has a sealing coat thereon whereby to retain water against the face of the setting concrete.-

15. A mold-form member according to claim 13 in which the face of the board opposite said hydrophilic coat has a moisture barrier coat thereon whereby to retain water against the face of the setting concrete. l l

16. A mold-form member according to claim 13 in which the face of the 'board opposite said hydrophilic coat ha a sealing coat of asphalt thereon which is su stantially non-tackyup to temperatures of 140 F. whereby to retain water against the setting concrete.

17. A mold-form member for molding poured hydraulic mixes of concrete and the like, comprising a water absorptive board of interfeltd ber, a hydrophilic coat on-said board discon tinuous in extent and providing interconnected coatings on surface ibers with pores from the interior of the board opening through the coated bers, said coat4 serving to prevent bonding of the fibers to the set hydraulic material, and a wetting agent available` at the surface of the board, said agent being active upon'contact with the poured mix to facilitate the rapid entry of Ventrapped air into the board through said coat,

and a sealing coat on the other face of the board serving to minimize the loss of water from the board, whereby the wet board preserves wet conv tact with the setting mix.

' ting mix against a mold form having water'` 18. The method of forming hydraulicrmixes of cement, concrete and the like to provide improved surfaces thereof against a mold form which comprises placing a plastic hydraulic setsoluble wetting agent available adjacent the sur-v face thereof, which mold form is porous to air and water, capable of absorbing water from thev mix and incapable of bonding to the inal set mass, whereby dissolving of said wetting agent by water of the mix breaks air-bubbles at the interface of said mixand s aid mold form prior to the loss of plasticity in the mix immediately adjacent said mold form, said bubbles being weakened by the local introduction into the water of the mix adjacent the mold of said wetting agent carried by the mold, whereby the breaking of theair-bubbles permits escape of the air in said bubbles into the porous mold, the still plastic mass being mobile to close the space and avoid forming pits'.J CLARK 'C. HERITAGE.

W. BARTLET'I JONES.

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