Water resistant cementitious article and method for preparing same

CROSS-REFERENCE TO RELATED APPLICATIONS

0001This patent application claims the benefit of <patcit id="pcit0001" dnum="US73831607A" dnum-type="L"><text>U.S. Patent Application No. 11/738,316, filed April 20, 2007</text></patcit> and <patcit id="pcit0002" dnum="US88948707P" dnum-type="L"><text>U.S. Provisional Patent Application No. 60/889,487, filed February 12, 2007</text></patcit>.

BACKGROUND OF THE INVENTION

0002Cementitious articles, such as gypsum board and cement board, are useful in a variety of applications, some of which require a degree of water resistance. Traditional paper-faced cementitious articles do not always perform wall under high moisture conditions, or upon exposure to the outdoors. Thus, for such applications, it is often desirable to use a cementitious article that is faced with a glass or polymer-based fiber mat instead of paper. It also is advantageous to use additives in the cementitious core that improve the water resistance of the core material itself.

0003The manufacturing process of cementitious articles, such as gypsum board and cement board, typically involves depositing a cementitious slurry over a first facing material and covering the wet slurry with a second facing material of the same type, such that the cementitious slurry is sandwiched between the two facing materials. Thereafter, excess water is removed from the slurry by drying. The cementitious slurry is allowed to harden to produce a solid article prior to final drying.

0004The manufacturing process of cementitious articles, thus, often requires the facing material to be sufficiently permeable that excess water can be removed from the cementitious slurry in the drying process. For example, non-woven fiberglass mat is often used as a facing material, in which the space between the fibers provides permeability. The permeability of the fibrous facing materials, however, makes the manufacturing process more difficult because the cementitious slurry deposited on the fibrous mat facing material tends to penetrate the mat causing slurry build-up on the forming table and assembly line. The slurry build-up must be removed periodically. Increasing the viscosity of the slurry can reduce the amount of slurry that penetrates the fibrous mat facing material, but the required higher viscosity is not always optimum for use in existing plant production processes due, for instance, to changes in mixing, setting, drying, or hardening characteristics.

0005Furthermore, the permeability of the fibrous mat facing material also reduces the water-resistance of the cementitious article because it allows water to penetrate the mat and contact the cementitious core during use. In order to alleviate this problem, exterior coatings of hydrophobic resins are sometimes applied. However, this generally requires an additional post-manufacturing step to be employed, adding cost and inconvenience.

0006Another approach is to further increase the water resistance of the cementitious core material by including hydrophobic additives in the cementitious slurry. A preferred additive for this purpose is a siloxane oil. However, methods of employing such additives require further improvement in their implementation and effectiveness.

0007<patcit id="pcit0003" dnum="US20050202742A1"><text>US 2005/0202742 A1</text></patcit> discloses a fiber mat faced gypsum board made by contacting a gypsum slurry for forming a set gypsum core with a non-coated side of a pre-coated fiber mat.

0008Thus, there remains a desire for new water resistant cementitious articles, as well as methods of preparing such articles.

BRIEF SUMMARY OF THE INVENTION

0009It is the object of the present invention to overcome the above mentioned problems.

0010This object is solved by the fibrous mat-faced cementitious article according to claim 1 and the method of preparing a fibrous mat-faced cementitious article according to claim 12.

0011The respective dependent claims describe advantageous developments of the article and the method.

0012In one aspect, the invention provides a fibrous mat-faced cementitious article comprising (a) a cementitious core, and (b) a first fibrous mat comprising polymer or mineral fibers and a hydrophobic finish on at least one surface thereof, wherein the hydrophobic finish is in contact with the cementitious core.

0013In another aspect, the invention provides a method of preparing a fibrous mat-faced cementitious article comprising (a) depositing a cementitious slurry on a first fibrous mat comprising polymer or mineral fibers and a hydrophobic finish on at least one surface thereof, wherein the cementitious slurry is deposited on the hydrophobic finish, and (b) allowing the cementitious slurry to harden, thereby providing a fibrous mat-faced cementitious article.

0014The fibrous mat-faced cementitious article according to the invention may comprise <ol id="ol0001" compact="compact"><li>(a) a cementitious core, and</li><li>(b) a first fibrous mat comprising polymer or mineral fibers and a hydrophobic finish on at least one surface thereof, wherein the hydrophobic finish is in contact with the cementitious core.</li></ol>

0015The hydrophobic finish may among others comprise talc, wax, a hydrophobic resin, a silicone-based compound, a fatty acid or salt thereof, polyethylene glycol, a hydrocarbon or fluorocarbon surfactant having 12 or more carbon atoms, or a combination thereof.

0016The hydrophobic finish can provide a layer having a thickness of at least 25 microns.

0017Polymer or mineral fibers can for example be glass fibers, polyester fibers, or a combination thereof. The cementitious article of the invention may further comprise a second fibrous mat comprising polymer or mineral fibers, wherein the cementitious core is disposed between the first fibrous mat and the second fibrous mat.

0018The cementitious core can be substantially free of mineral or paper fibers.

0019The cementitious core may comprise a hydrophobic additive, which is preferably a silicone-based material.

0020The cementitious core can comprise unstable and stable soaps.

0021The cementitious core can further comprise a polyphosphate, which for example can be sodium trimetaphosphate.

0022The method of preparing a fibrous mat-faced cementitious article according to the invention can comprise (a) depositing a cementitious slurry on a first fibrous mat comprising polymer or mineral fibers and a hydrophobic finish on at least one surface thereof, wherein the cementitious slurry is deposited on the hydrophobic finish, and (b) allowing the cementitious slurry to harden, thereby providing a fibrous mat-faced cementitious article.

0023In the method the hydrophobic finish can comprise talc, wax, a hydrophobic resin, a silicone-based compound, a fatty acid or salt thereof, polyethylene glycol, a hydrocarbon or fluorocarbon surfactant having 12 or more carbon atoms, or a combination thereof.

0024The method can further comprise depositing a hydrophobic finish on the fibrous mat before depositing the cementitious slurry on the first fibrous mat.

0025The method can further comprise drying the hydrophobic finish before depositing the cementitious slurry on the first fibrous mat.

0026In the method, the hydrophobic finish can provide a layer having a thickness of at least about 25 microns.

0027In the method, the polymer or mineral fibers can be glass fibers, polyester fibers, or a combination thereof.

0028The method can further comprise contacting the cementitious slurry with a second fibrous mat prior to allowing the cementitious slurry to harden, wherein the cementitious slurry can be disposed between the first fibrous mat and the second fibrous mat.

0029The cementitious slurry can be substantially free of paper or mineral fibers.

0030The cementitious slurry can comprise a hydrophobic additive, which can for example be a siloxane.

0031The cementitious slurry can be mixed in a mixer comprising a discharge conduit, and foam can be added to the cementitious slurry in the discharge conduit prior to depositing the slurry on the first fibrous mat.

0032The cementitious slurry can comprise pre-blended unstable and stable soaps.

0033The cementitious slurry can comprise a polyphosphate, as for example sodium trimetaphosphate.

0034These and other advantages of the present invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.

DETAILED DESCRIPTION OF THE INVENTION

0035Embodiments of a fibrous mat-faced cementitious article according to the invention comprise (a) a cementitious core, and (b) a first fibrous mat comprising polymer or mineral fibers and a hydrophobic finish on at least one surface thereof, wherein the hydrophobic finish is in contact with the cementitious core. Desirably, the hydrophobic finish prevents the cementitious core of the article from penetrating the first fibrous mat to any substantial degree during manufacture.

0036The first fibrous mat comprises any suitable type of polymer or mineral fiber, or combination thereof. Non-limiting examples of suitable fibers include glass fibers, polyamide fibers, polyaramide fibers, polypropylene fibers, polyester fibers (e.g., polyethylene teraphthalate (PET)), polyvinyl alcohol (PVOH), polyvinyl acetate (PVAc), cellulosic fibers (e.g., cotton, rayon, etc.), and the like, as well as combinations thereof. Furthermore, the fibers of the mat can be hydrophobic or hydrophilic, coated or uncoated. Of course, the choice of fibers will depend, in part, on the type of application in which the cementitious article is to be used. For example, when the cementitious article is used for applications that require heat or fire resistance, appropriate heat or fire resistant fibers should be used in the fibrous mat.

0037The first fibrous mat can be woven or non-woven; however, non-woven mats are preferred. Non-woven mats comprise fibers bound together by a binder. The binder can be any binder typically used in the mat industry. Suitable binders include, without limitation, urea formaldehyde, melamine formaldehyde, stearated melamine formaldehyde, polyester, acrylics, polyvinyl acetate, urea formaldehyde or melamine formaldehyde modified or blended with polyvinyl acetate or acrylic, styrene acrylic polymers, and the like, as well as combinations thereof. Suitable fibrous mats include commercially available mats used as facing materials for cementitious articles.

0038The first fibrous mat of the cementitious article comprises a hydrophobic finish on at least one surface thereof, which is in contact with the cementitious core. Any hydrophobic finish material can be used. Preferably, the hydrophobic finish provides a surface with a degree of hydrophobicity such that water applied to the surface exhibits a contact angle of about 70° or greater, such as about 70° to about 130°, or about 90° or greater, such as about 90° to about 120°. The contact angle can be measured by any suitable technique.

0039Examples of suitable hydrophobic finish materials include, without limitation, compositions comprising, consisting essentially of, or consisting of talc, wax, silicone-based compounds (e.g., silanes or siloxanes), hydrophobic resins, fatty acids (e.g., oleic acid) and salts (e.g., multivalent salts) thereof, polyethylene glycol (PEG), and long-chain hydrocarbon and fluorocarbon surfactants (e.g., having 12 or more carbon atoms), as well as combinations thereof.

0040The finish material can be applied to the first fibrous mat as a liquid or solid material (e.g., resin, wet-dispersed powder, dry powder, or film) by any of various methods known in the art. For instance, the hydrophobic finish materials can be applied by brushing, spraying, rolling, pouring, dipping, sifting, or overlaying the hydrophobic finish material. Solid materials, such as powders, can be dispersed prior to application using any common solvent (e.g, water, alcohols, etc.) or dispersant, provided the solvent or dispersant does not react adversely with the fibrous mat materials. Solvents that etch the surface fibers of the fibrous mat, and thereby enhance the ability of the finish material to adhere to the mat, also can be used. Preferably, any solvent or dispersant used is easily dried and does not leave a residue that prevents the finish from adhering to the fibrous mat. Liquid or dispersed finish materials can have any viscosity suitable for application to the fibrous mat. Typically, the viscosity of a liquid or dispersed finish material will be from about 50-200 Kreb's units (KU) (about 300-20,000 cP), such as about 80-150 KU (about 800-8,000 cP).

0041Recognizing that the surface of the fibrous mat is an irregular surface, the finish material need not provide a finish that is completely continuous. When a liquid or powder finish composition is used, for instance, the finish material may fall within the voids between the fibers of the mat leaving gaps or holes in the finish. However, the finish material preferably is applied in an amount sufficient to provide a finish that is continuous and, desirably, coextensive with the dimensions of the first fibrous mat.

0042The hydrophobic finish applied to the first fibrous mat is preferably in the form of a layer. The layer, desirably, is thick enough to slow or prevent the penetration of cementitious slurry through the first fibrous mat during production. Without wishing to be bound by any particular theory, it is believed that the hydrophobic layer slows or prevents slurry penetration due to the reduced surface tension of the cementitious slurry on the hydrophobic layer as compared to the fibrous mat in the absence of the hydrophobic layer and/or by physically blocking the pore space of the fibrous mat. Generally, the finish will provide a layer over the mat (and over any resinous binder used to bind the fibers of the mat) with an average thickness of at least 25 microns (e.g., at least 25 to 500 microns), at least 100 microns (e.g., 100 to 500 microns), or at least 200 microns (e.g., 200 to 500 microns, or 200 to 400 microns), or even at least 300 microns (e.g., 300 to 500 microns, or 300 to 400 microns).

0043According to a preferred aspect of the invention, the first fibrous mat is not substantially embedded in the cementitious core. Preferably, less than about 50% of the thickness of the mat is embedded in the cementitious core, more preferably less than about 30%, less than about 15%, less than about 10%, or even less than about 2% (e.g., less than about 1 %) of the thickness of the mat is embedded in the cementitious core. Without wishing to be bound by any particular theory, it is believed that the hydrophobic finish of the first fibrous mat prevents, to at least some degree, the first fibrous mat from becoming embedded in the cementitious core during production. In a related and preferred aspect of the invention, the cementitious core adheres, at least in part, to the hydrophobic finish.

0044It will be appreciated that the first fibrous mat has two facing surfaces: an outwardly facing surface and a surface facing the cementitious core. In accordance with the invention, the surface of the first fibrous mat facing the cementitious core comprises a hydrophobic finish. The outwardly facing surface need not comprise a hydrophobic finish. However, according to one embodiment of the invention, the outwardly facing surface of the fibrous mat also can comprise a hydrophobic finish as described herein. Alternatively, the outwardly facing surface can be otherwise treated by any method known in the art, or can remain untreated.

0045The cementitious article optionally can comprise a second fibrous mat comprising polymer or mineral fibers, wherein the cementitious core is disposed between the first fibrous mat and the second fibrous mat. The second fibrous mat can be the same or different from the first fibrous mat. Furthermore, the second fibrous mat can comprise a hydrophobic finish as described herein, or can be free of such a finish. When the cementitious article is in the form of a board or panel (e.g., gypsum board, cement board, etc.), the second fibrous mat is preferably the same as the first fibrous mat, both in material and orientation relative to the cementitious core, or has sufficiently similar expansion and contraction properties to the first fibrous mat, such that warping of the cementitious article is reduced or eliminated. When the second fibrous mat is the same as the first fibrous mat, it should be understood that the first and second fibrous mats can be provided by a single continuous piece of material, for example, by folding a single piece of fibrous mat such that it wraps around the cementitious core.

0046The cementitious core can comprise any material, substance, or composition containing or derived from hydraulic cement, along with any suitable additives. Non-limiting examples of materials that can be used in the cementitious core include Portland cement, sorrel cement, slag cement, fly ash cement, calcium alumina cement, water-soluble calcium sulfate anhydrite, calcium sulfate α-hemihydrate, calcium sulfate β-hemihydrate, natural, synthetic or chemically modified calcium sulfate hemihydrates, calcium sulfate dihydrate ("gypsum," "set gypsum," or "hydrated gypsum"), and mixtures thereof. As used herein, the term "calcium sulfate material" refers to any of the forms of calcium sulfate referenced above.

0047The additives can be any additives commonly used to produce cementitious articles, such as gypsum board or cement board. Such additives include, without limitation, structural additives such as mineral wool, continuous or chopped glass fibers (also referred to as fiberglass), perlite, clay, vermiculite, calcium carbonate, polyester, and paper fiber, as well as chemical additives such as foaming agents, fillers, accelerators, sugar, enhancing agents such as phosphates, phosphonates, borates and the like, retarders, binders (e.g., starch and latex), colorants, fungicides, biocides, and the like. Examples of the use of some of these and other additives are described, for instance, in <patcit id="pcit0004" dnum="US6342284B"><text>U.S. Patents 6,342,284</text></patcit>, <patcit id="pcit0005" dnum="US6632550B"><text>6,632,550</text></patcit>, <patcit id="pcit0006" dnum="US6800131B"><text>6,800,131</text></patcit>, <patcit id="pcit0007" dnum="US5643510A"><text>5,643,510</text></patcit>, <patcit id="pcit0008" dnum="US5714001A"><text>5,714,001</text></patcit>, and <patcit id="pcit0009" dnum="US6774146B"><text>6,774,146</text></patcit>, and <patcit id="pcit0010" dnum="US20040231916A1"><text>U.S. Patent Publications 2004/0231916 A1</text></patcit>, <patcit id="pcit0011" dnum="US20020045074A1"><text>2002/0045074 A1</text></patcit> and <patcit id="pcit0012" dnum="US20050019618A1"><text>2005/0019618 A1</text></patcit>.

0048Preferably, the cementitious core comprises a calcium sulfate material, Portland cement, or mixture thereof. Advantageously, the cementitious core also comprises a hydrophobic agent, such as a silicone-based material (e.g., a silane, siloxane, or silicone-resin matrix), in a suitable amount to improve the water resistance of the core material. It is also preferred that the cementitious core comprise a siloxane catalyst, such as magnesium oxide (e.g., dead burned magnesium oxide), fly ash (e.g., Class C fly ash), or a mixture thereof. The siloxane and siloxane catalyst can be added in any suitable amount, and by any suitable method as described herein with respect the method of preparing a water-resistant cementitious article of the invention, or as described, for example, in <patcit id="pcit0013" dnum="US20060035112A1"><text>U.S. Patent Publications 2006/0035112 A1</text></patcit> or <patcit id="pcit0014" dnum="US20070022913A1"><text>2007/0022913 A1</text></patcit>. Desirably, the cementitious core also comprises strength-improving additives, such as phosphates (e.g., polyphosphates as described in <patcit id="pcit0015" dnum="US6342284B"><text>U.S. Patents 6,342,284</text></patcit>, <patcit id="pcit0016" dnum="US6632550B"><text>6,632,550</text></patcit>, and <patcit id="pcit0017" dnum="US6800131B"><text>6,800,131</text></patcit> and <patcit id="pcit0018" dnum="US20020045074A1"><text>U.S. Patent Publications 2002/0045074 A1</text></patcit>, <patcit id="pcit0019" dnum="US20050019618A1"><text>2005/0019618 A1</text></patcit>, and <patcit id="pcit0020" dnum="US20070022913A1"><text>2007/0022913 A1</text></patcit>) and/or pre-blended unstable and stable soaps (e.g., as described in <patcit id="pcit0021" dnum="US5683635A"><text>U.S. Patents 5,683,635</text></patcit> and <patcit id="pcit0022" dnum="US5643510A"><text>5,643,510</text></patcit>). The cementitious core can comprise paper or glass fibers, but is preferably substantially free of paper and/or glass fibers (e.g., comprises less than about 1 wt.%, less than about 0.5 wt.%, less than about 0.1 wt.%, or even less than about 0.05 wt.% of paper and/or glass fibers, or contains no such fibers).

0049The cementitious article can be any of any type or shape suitable for a desired application. Non-limiting examples of cementitious articles include gypsum panels and cement panels of any size and shape.

0050The cementitious article can be prepared by any suitable method including, but not limited to, the inventive methods described herein. Embodiments of a method of preparing a fibrous mat-faced cementitious article according to the invention comprise (a) depositing a cementitious slurry on a first fibrous mat comprising polymer or mineral fibers, wherein the first fibrous mat comprises a hydrophobic finish on at least one surface thereof, and the cementitious slurry is deposited on the hydrophobic finish, and (b) allowing the cementitious slurry to harden, thereby providing a fibrous mat-faced cementitious article.

0051The method of preparing a cementitious article in accordance with the invention can be conducted on existing gypsum board manufacturing lines used to make fibrous mat-faced cementitious articles known in the art. Briefly, the process typically involves discharging a fibrous mat material onto a conveyor, or onto a forming table that rests on a conveyer, which is then positioned under the discharge conduit (e.g., a gate-canister-boot arrangement as known in the art, or an arrangement as described in <patcit id="pcit0023" dnum="US6494609B"><text>U.S. Patents 6,494,609</text></patcit> and <patcit id="pcit0024" dnum="US6874930B"><text>6,874,930</text></patcit>) of a mixer. The components of the cementitious slurry are fed to the mixer comprising the discharge conduit, where they are agitated to form the cementitious slurry. Foam can be added in the discharge conduit (e.g., in the gate as described, for example, in <patcit id="pcit0025" dnum="US5683635A"><text>U.S. Patents 5,683,635</text></patcit> and <patcit id="pcit0026" dnum="US6494609A"><text>6,494,609</text></patcit>). The cementitious slurry is discharged onto the fibrous mat facing material. The slurry is spread, as necessary, over the fibrous mat facing material and optionally covered with a second facing material, which may be a fibrous mat or other type of facing material (e.g., paper, foil, plastic, etc.). The wet cementitious assembly thereby provided is conveyed to a forming station where the article is sized to a desired thickness, and to one or more knife sections where it is cut to a desired length to provide a cementitious article. The cementitious article is allowed to harden, and, optionally, excess water is removed using a drying process (e.g., by air-drying or transporting the cementitious article through a kiln). Each of the above steps, as well as processes and equipment for performing such steps, are known in the art. It also is common in the manufacture of cementitious articles such as gypsum and cement board to deposit a relatively dense layer of slurry onto a facing material before depositing the primary slurry, and to use vibration in order to eliminate large voids or air pockets from the deposited slurry. Also, hard edges, as known in the art, are sometimes used. These steps or elements (dense slurry layer, vibration, and/or hard edges) optionally can be used in conjunction with the invention.

0052All aspects of the first fibrous mat used in accordance with the method of preparing a cementitious article are as described herein with respect to the cementitious article of the invention.

0053Although the cementitious slurry is in contact with the hydrophobic finish of the first fibrous mat, the cementitious slurry preferably does not substantially penetrate the first fibrous mat, thereby preventing the first fibrous mat from embedding in the cementitious slurry to any substantial degree. Preferably, the cementitious slurry penetrates less than about 50% of the thickness of the mat, more preferably less than about 30%, less than about 15%, less than about 10%, or even less than about 2% (e.g., less than about 1%) of the thickness of the mat. Most preferably, the cementitious slurry does not penetrate at all beyond the hydrophobic finish on the mat. According to a related and preferred aspect of the invention, the cementitious slurry preferably adheres, at least in part, to the hydrophobic finish.

0054The hydrophobic finish can be applied to the first fibrous mat prior to delivering the first fibrous mat to the manufacturing line. Alternatively, the hydrophobic finish can be applied to the first fibrous mat on the manufacturing line. In this respect, the method of the invention can further comprise depositing a hydrophobic finish on the first fibrous mat before depositing the cementitious slurry on the first fibrous mat. Any suitable hydrophobic finish material can be used, as previously described herein. The hydrophobic finish can be deposited on the first fibrous mat by any of various techniques known in the art, such as by brushing, spraying, rolling, pouring, dipping, sifting, or overlaying the hydrophobic finish material.

0055The hydrophobic finish, when applied as a liquid, preferably is dried before depositing the cementitious slurry on the first fibrous mat. The hydrophobic finish can be dried by any suitable method, such as by applying heat to the finish or to the mat comprising the finish.

0056Optionally, the method of preparing a fibrous mat-faced cementitious article can further comprise contacting the cementitious slurry with a second fibrous mat prior to allowing the cementitious slurry to harden, wherein the cementitious slurry is disposed between the first fibrous mat and the second fibrous mat. All other aspects of the first and second fibrous mats are as described with respect to the cementitious article of the invention.

0057The cementitious slurry comprises any of the cementitious materials and additives previously described as suitable or preferred with respect to the cementitious core of the cementitious article, along with sufficient water to provide a suitable viscosity. When measured by the slump test, the cementitious slurry will typically produce a patty with a diameter of about 5" to about 8" (or about 10 cm to about 20 cm), such as about 6" to about 7" (or about 15 cm to about 18 cm). Procedures for measuring the viscosity of a slurry using the slump test are known in the art. Briefly, a 2" (or 5 cm) diameter tube is filled with slurry to a height of 4" (10 cm). Within 5 seconds from sampling the slurry from the manufacturing line, the slurry is released from the tube onto a flat, level surface and allowed to spread into a patty. When the slurry has stopped spreading, the widest diameter of the slurry patty is measured (in the case of non-circular (e.g., elliptical) slurry patty, the widest diameter of the slurry patty is averaged with the diameter of the slurry patty in the direction perpendicular to the widest diameter).

0058Other aspects of the method of preparing a fibrous mat-faced cementitious article are as described herein with respect to the cementitious article of the invention. Those aspects of the method of preparing a fibrous mat-faced cementitious article not specifically described herein can be supplied by the techniques known and used in the manufacture of conventional cementitious articles, especially fibrous mat-faced cementitious articles.

0059The cementitious slurry can be deposited onto a substrate in accordance with known methods and on existing manufacturing lines, as described herein with respect to the method of preparing a fibrous mat-faced cementitious article.

0060It is especially advantageous, to employ first and a second fibrous mat, wherein the cementitious slurry is disposed between the fibrous mats. Suitable such fibrous mats, hydrophobic finishes, and methods for the use thereof to provide a cementitious article, are as described herein with respect to the fibrous mat-faced cementitious article and method for preparing a fibrous mat-faced cementitious article of the invention.

0061All other aspects of the method of preparing a water-resistant cementitious article are as described herein with respect to the fibrous mat-faced cementitious article or the method of preparing a mat-faced cementitious article. Aspects of the method of preparing water-resistant cementitious article not specifically described herein can be supplied by the techniques known and used in the manufacture of conventional cementitious articles, especially fibrous mat-faced cementitious articles.

Example 1

0062The following example illustrates the preparation of a fibrous-mat faced cementitious article in accordance with the invention.

0063Two types of fibrous mats are prepared: a first mat comprising all glass fibers and a second mat comprising a blend of 85 wt.% glass fibers and 15 wt.% polyester fibers. Both mats are non-woven and comprised a 19 wt.% melamine formaldehyde/acrylic binder.

0064A cementitious slurry is prepared using the formulation provided in Table 1 in a board mixer. The siloxane component of the slurry is dispersed in water (e.g., 4.1-4.4 wt.% siloxane in water dispersion) using a high shear mixer (e.g., the 312/45 MS high shear mixer (20 hp, 3600 rpm) manufactured by Silverson Machines, Inc., East Longmeadow, MA, and the X-Series Mixer emulsifiers (60 Hz, 3,600 rpm) manufactured by Charles Ross &amp; Son Company, Hauppauge, NY), and introduced into the gauging water used to prepare the slurry.

0065The fibrous mat is positioned for application to the face (formed down) and the back (formed up) of the cementitious panel. The mat is passed through a tensioning and alignment system, and the face mat is creased to form the desired thickness (e.g, 5/8") and desired edge (e.g., square) at the desired board width (e.g., 48"). Preferably, a hydrophobic finish is applied to the face mat. The face mat is passed under the board mixer, and the cementitious slurry is deposited onto the face mat. A densified layer is not deposited prior to depositing the cementitious slurry, and any slurry vibration apparatuses are turned off to help reduce slurry penetration through the mat. <tables id="tabl0001" num="0001"><table frame="all"><title>Table 1</title><tgroup cols="2"><colspec colnum="1" colname="col1" colwidth="115mm" /><colspec colnum="2" colname="col2" colwidth="51mm" /><thead><row><entry>Component</entry><entry align="center">Average</entry></row></thead><tbody><row><entry valign="bottom">Stucco</entry><entry align="center" valign="bottom">2140.6 lbs./MSF (10500 g/m²)</entry></row><row><entry valign="bottom">Gauging water + siloxane water + siloxane</entry><entry align="center" valign="bottom">826.6 lbs./MSF (4050 g/m²)</entry></row><row><entry valign="bottom">Siloxane water</entry><entry align="center" valign="bottom">255.0 lbs./MSF (1250 g/m²)</entry></row><row><entry valign="bottom">Siloxane</entry><entry align="center" valign="bottom">11.27 lbs./MSF (55 g/m²)</entry></row><row><entry valign="bottom">MgO</entry><entry align="center" valign="bottom">1.00 lbs./MSF (5 g/m²)</entry></row><row><entry valign="bottom">Flyash</entry><entry align="center" valign="bottom">8.00 lbs./MSF (40 g/m²)</entry></row><row><entry valign="bottom">Foam water</entry><entry align="center" valign="bottom">95.85 lbs./MSF (470 g/m²)</entry></row><row><entry valign="bottom">Foam air</entry><entry align="center" valign="bottom">14.35 cu. ft./MSF (0.044 km³/m²)</entry></row><row><entry valign="bottom">Soap - Pre-blended 90% unstable to 10% stable soap (Hyonic 25 FM - from GEO Specialty Chemicals)</entry><entry align="center" valign="bottom">0.459 lbs./MSF (2.3 g/m²)</entry></row><row><entry valign="bottom">Ground gypsum accelerator (5 wt.% sugar)</entry><entry align="center" valign="bottom">6.76 lbs./MSF (11 g/m²)</entry></row><row><entry valign="bottom">Sodium trimetaphosphate</entry><entry align="center" valign="bottom">0.77 lbs./MSF (3.7 g/m²)</entry></row><row><entry valign="bottom">Thickness</entry><entry align="center" valign="bottom">0.63 inches (1.6 cm)</entry></row><row><entry valign="bottom">Dispersant</entry><entry align="center" valign="bottom">10.17 lbs./MSF (50 g/m²)</entry></row><row><entry valign="bottom">Fiber (paper and/or glass)</entry><entry align="center" valign="bottom">0.00 lbs./MSF</entry></row><row><entry valign="bottom">Glass water</entry><entry align="center" valign="bottom">465.0 lbs./MSF (50 g/m²)</entry></row><row><entry valign="bottom">Total water</entry><entry align="center" valign="bottom">1393.1 lbs./MSF (6825 g/m²)</entry></row><row><entry valign="bottom">WSR (Water Stucco Ratio)</entry><entry align="center" valign="bottom">65.1%</entry></row></tbody></tgroup></table></tables>

0066The creased face mat with the slurry in-place is formed into an envelope and passed under the forming plate. At the point where the formed face mat enters the forming plate, the back mat is placed in contract with the edges of the face mat. A bead of synthetic adhesive is used to bond the face glass mat to the back glass mat at the point where the mats intersected. Slurry does not contact the face and back glass mats at this intersection.

0067The completed glass mat envelope, filled with slurry, exits the forming plate and is transferred to the board belt. Guides keep the edges in the proper position until the slurry hydrates at a point about 30 seconds down the board belt, at which point the edges are self-supporting. The board is moved further down the line until it becomes self supporting. Thereafter, the board is cut to slightly longer than its desired finished length with a board knife. The board is inverted and moved into the kiln to remove the excess water.

0068The resulting product is a fibrous mat-faced cementitious product with improved water resistance.

Example 2

0069The following example illustrates the effectiveness of a hydrophobic finish material applied to a fibrous mat facing material in preventing the penetration of a cementitious slurry through the fibrous mat.

0070Talc powder (Talcron 40-26, particle size 5 microns) dispersed in water containing 0.05 wt.% tripotassium polyphosphate (dispersant) at various solid loading levels and viscosities is applied to non-woven glass fiber mats to coat the mats at a thickness of 5 mil or 15 mil (based on wet film thickness). The solid loading level, viscosity, and thickness of the finishes are provided in Table 2. Finishes 5-7 also contain a hydroxyethylcellulose viscosity enhancer (0.05 wt.%). Finish 7 further includes 1 wt.% white wax. Thereafter, a cementitious slurry is deposited over the finish material. <tables id="tabl0002" num="0002"><table frame="all"><title>Table 2</title><tgroup cols="5"><colspec colnum="1" colname="col1" colwidth="20mm" /><colspec colnum="2" colname="col2" colwidth="26mm" /><colspec colnum="3" colname="col3" colwidth="20mm" /><colspec colnum="4" colname="col4" colwidth="24mm" /><colspec colnum="5" colname="col5" colwidth="51mm" /><thead><row><entry valign="top">Finish</entry><entry valign="top">Thickness (mil)</entry><entry valign="top">Solids (%)</entry><entry valign="top">Viscosity (KU)</entry><entry valign="top">Results</entry></row></thead><tbody><row><entry>1</entry><entry>5</entry><entry>50</entry><entry>70</entry><entry>Reduced slurry penetration</entry></row><row><entry>2</entry><entry>15</entry><entry>50</entry><entry>70</entry><entry>No slurry penetration</entry></row><row><entry>3</entry><entry>5</entry><entry>60</entry><entry>119</entry><entry>No slurry penetration</entry></row><row><entry>4</entry><entry>15</entry><entry>60</entry><entry>119</entry><entry>No slurry penetration</entry></row><row><entry>5</entry><entry>5</entry><entry>20</entry><entry>83</entry><entry>Reduced slurry penetration</entry></row><row><entry>6</entry><entry>15</entry><entry>20</entry><entry>83</entry><entry>Reduced slurry penetration</entry></row><row><entry>7</entry><entry>5</entry><entry>20</entry><entry>83</entry><entry>Reduced slurry penetration</entry></row><row><entry>8 (control)</entry><entry>(n/a)</entry><entry>(n/a)</entry><entry>(n/a)</entry><entry>High degree of slurry penetration</entry></row></tbody></tgroup></table></tables>

0071The amount of slurry penetration is visually inspected and compared to a control, which is provided by applying the same slurry to a glass fiber mat that is identical to the mats used to test finishes 1-7, but comprises no finish material.

0072By comparison to the control mat, a lesser amount of slurry will penetrate the mats comprising a finishing material, showing that the application of a hydrophobic finish to a fibrous mat facing material reduces or eliminates slurry penetration through the fibrous mat.