Gypsum board

Abstract: A backer board (10) provides a base to which ceramic tile (38) may be bonded for use in a bathtub or shower area, the board being made by forming a gypsum core board (20) with fiber glass laminated composite facings (22, 24) which include an inner fiber glass scrim (28), an outer fiber glass non-woven mat (30) and an acrylic film (32), which film is formed of an acrylic latex of a class commonly employed as an ingredient in Portland cement mortar for applying ceramic tile, such a mortar (40) being used to bond tile (38) to the base board (10).

Description: This invention relates to a novel gypsum board and particularly to a backer board for wet areas, such as behind ceramic tile in bathtub and shower areas. The invention further relates to a wet area wall structure comprising a gypsum board and a plurality of ceramic tiles, to a method of making a gypsum board and to the use of a specific film on a front face of a gypsum board. U.S. Patent No. 4,647,496 discloses a fibrous mat-faced gypsum support surface in the exterior structure of a building with insulating material adhered thereover and an exterior finishing material which may be an acrylic resin based composition or a Portland cement stucco. Woven glass cloth, glass fiber scrim or a glass fiber mesh may be embedded in the exterior finishing material, or between the insulating material and the exterior finishing material as a reinforcing component. The fibrous mat-faced gypsum support surface is preferably a set gypsum core faced with a fibrous mat. The mat can comprise continuous or discrete strands of fibers and be woven or nonwoven, but preferably it is fiber glass filaments oriented in random pattern, bound together with a resin binder, and preferably on both surfaces of the core. Canadian Patent No. 993,779 also discloses a gypsum core board with facings formed of woven or unwoven porous glass fiber cover sheets, the woven normally being found more expensive. U.S. Patent No. 3,312,585 discloses a gypsum board for use as a backer board for behind ceramic tile in wet areas, formed of a paper covered gypsum core, plus a water impervious film, such as of polyvinyl chloride covering the front face of the board and at least one longitudinal edge. U.S. Patent No. 4,504,533 discloses a construction board the gypsum core of which is faced with a laminate of an inner mineral fiber web and an outer non-woven fiber web, the inner web being embedded in the core. Document US-A-3 993 822 discloses a gypsum board comprising a core consisting of a soft, watery, paste-like mixture of gypsum, water and fibres which has been hardened; a first face with facing material thereon and a second face with facing material thereon; said facing material on at least one of the two faces being a mineral fibre laminated composite facing including two plies, said two plies being a fibreglass layer or cloth,i.e. a woven mineral fibre scrim, adhered to said gypsum core, and a layer of - inter alia - a glass fibre fleece, i.e. a nonwoven mineral fibre mat disposed outward of said scrim. The present invention provides a novel water resistant gypsum board having on at least one face a laminated composite facing of an inner at least semi-woven fiber scrim and an outer non-woven fiber mat, the fibers of both layers preferably being glass fiber, the outer mat having a water based latex film formed thereon. More especially, the invention provides a gypsum board, for use in wet areas for application thereto of ceramic tile, said board comprising a set gypsum core, a front face with facing material thereon and a back face with facing material thereon, said facing material on at least said front face being a mineral fiber laminated composite facing, said composite facing including two plies, said two plies being a woven mineral fiber scrim adhered to said gypsum core and a nonwoven mineral fiber mat disposed outward of said scrim, said fiber mat on said front face having on its side not adhering to the scrim a film derived from a water-based latex, the material of said film extending through said laminated composite facing into said gypsum core. The two plies of the composite facings are advantageously laminated and bonded together prior to incorporation with the gypsum core, i.e., prior to the formation of the gypsum board. Following the formation of the gypsum board, the fibrous laminated composite facing on the front face of the gypsum board, which is most likely to be subjected to water, is coated with a water-based latex coating, preferably an acrylic latex coating. The mineral fiber is advantageously glass fiber in each layer. Advantageously, therefore, the board is made by a method comprising the steps of laminating a ply of glass fiber scrim to a ply of a nonwoven glass fiber mat, forming a gypsum slurry containing water repellent additives into board form with said laminated glass fiber composite forming a front face facing for said gypsum board, bonding said glass fiber composite to said gypsum core by causing said gypsum slurry to penetrate into said glass fiber scrim ply of said glass fiber composite, allowing said gypsum slurry to partially set, applying a resin film to said front face so that it penetrates through said face into the partially set gypsum board, and optionally severing said coated gypsum board into predetermined lengths, and drying said gypsum board or boards. In the preferred embodiment, the gypsum core includes, within its composition, water repellent chemicals, for example emulsions of asphalt and wax. The invention provides a gypsum board improved in its ability to withstand the dampness which often exists on the face of a board to which ceramic tile is applied, in bath and shower areas or the like, and its ability to have ceramic tile bonded thereto with a resultant extra strong bond. The invention further provides in a preferred embodiment a fiber glass faced gypsum board having markedly improved strength and visual appearance as a result of the novel placement of an outer layer of randomly directed, discontinuous fibers in a porous felted non-woven fiber form, over an inner layer of continuous long fibers in a woven form, in a multi-layer, latex coated facing on a gypsum board. The invention also provides a combination of such facings on a gypsum core with a water repellent composition to form a board over which ceramic tile may be applied to provide an improved wet area wall (see claim 9). The invention further provides the use of a specific film on a front face of a gypsum board, in accordance with independent claim 15. Preferred embodiments and advantages of the invention will be described by way of example only, in greater detail with reference to the accompanying drawings, in which: Fig. 1 is an isometric view of one form of gypsum board, made in accordance with the invention. Fig. 2 is an enlarged cross-sectional isometric view of the edge portion of the gypsum board of Fig. 1, taken on line 2-2 thereof. Fig. 3 is a face view of the top surface of the gypsum board of Fig. 1, coated with an acrylic latex, portions broken away showing the preferred semi-woven glass fiber inner layer continuous strands behind a non-woven random, discontinuous glass fiber outer surface, formed of felted, random, discontinuous glass fibers, and overlapping the wrapped around edge of the back face felted fiber layer. Fig. 4 is a face view of a ceramic tile wall intended for a bathtub, shower or other wet area, with portions broken away, showing the gypsum board of Fig. 3, covered with resin reinforced Portland cement mortar, covered with ceramic tile. Referring to the drawings, there is shown a gypsum board 10, having a front face 12, two side edges 14, a back face 16 and two ends 18. The gypsum board 10 is formed of a gypsum core 20, enclosed within a front face laminated composite facing 22 and a back face laminated composite facing 24. The front face composite facing 22 extends entirely throughout the extent of front face 12. The back face composite facing 24 extends throughout all of the back face 16 with only one layer of the composite facing 24 extending around each of the two side edges 14 and a short distance onto the front face 12 adjacent to each side edge 14. The front face composite facing 22, adjacent each side edge 14, overlaps the part of the back face composite facing 24 disposed thereat, forming a lapped joint 26 of the two composite facings 22, 24. The gypsum core 20 preferably includes water repellant additives, such as asphalt and wax which were added during manufacture of the gypsum board, in the form of a 10% by weight asphalt-wax emulsion, and about 0.5% by weight polyvinyl alcohol. The front face laminated composite facing 22 and the back face laminated composite facing 24 are both conveniently about .020 inch (about 0.5 mm) thick, formed essentially of two plies, preferably an inner semi-woven glass fiber scrim 28 and an outer nonwoven fiber glass mat 30. The scrim weight is about 11.3 pounds per thousand square feet and the mat weight is about 16.5 pounds per thousand square feet (about 55.2 and about 80.6 kg/thousand square metres respectively). The front face laminated composite facing 22 has formed thereon a thin acrylic film 32 which is the product of an application of an acrylic latex to the front face 12 just before severing of the continuously formed web of gypsum board into separate gypsum boards 10, and thus prior to drying of the gypsum boards 10, permitting curing of the film 32 during drying of the gypsum core 20. The acrylic latex which is applied is preferably a water dispersion of an acrylic polymer specifically designed for modifying Portland cement compositions, such as a Rohm and Haas Company additive identified by the trademark Rhoplex E-330. This particular aqueous acrylic emulsion is a white, milky liquid, of 47% solids, a 9.5 to 10.5 pH, a 50 cP (0.05 Pa s) maximum viscosity, a specific gravity of between 1 and 1.2, with freeze thaw stability to 5 cycles and a minimum film formation temperature of 10° to 12°C. It contains a maximum of 0.2% ammonia. By employing an acrylic polymer, to form film 32, which is preferably one used in modifying Portland cement compositions, the film 32 is caused to be substantially better in respect to its ability to bond to resin-enhanced mortars used for applying ceramic tile. The acrylic latex is applied using two vinyl rolls covered with a cloth sleeve, which apply 12-14 pounds of solids per thousand square feet (about 58.6 to about 68.4 kg/thousand square metres) of gypsum board. The acrylic latex penetrates completely through the very porous front face laminated composite facing 22 and on into the gypsum core, which still contains considerable excess water at the time the latex is applied, strengthening the core 20 in that portion of the core 20 which is most important in providing high shear values that contribute to bonding ceramic tile to the gypsum board. The acrylic latex also adds additional water resistance to the gypsum core. The portion of the back face laminated composite facing 24 which extends around each of the two side edges 14 and a short distance onto the front face 12, preferably consists solely of the outer nonwoven fiber glass mat 30. The side edge 34 of the semi-woven glass fiber scrim 28 of the back facing 24 will be seen in Fig. 2 to be located at the side edge 14 of the gypsum board back face 16. By omitting the scrim 28 of back facing 24 from the portion which extends around edges 14 and onto front face 12, manufacturing processes, particularly the severing of the formed board into separate gypsum boards 10, are made easier, requiring less energy and having less potential for damage to the end product. The semi-woven glass fiber scrim 28 has preferably a fiber count of 6 fibers/inch (about 2.4 per cm) in the cross machine direction and 10 fibers/inch (about 4 per cm) in the machine direction. The tensile strength in the cross machine direction is 122 pounds per inch, and in the machine direction is 107 pounds per inch (about 21.4 and about 18.7 N/mm respectively). The laminated composite facings 22, 24 are available, prebonded as a unitary two-ply composite, from the Milliken Corporation. During formation of the gypsum board 10, the lapped joint 26 is formed with a polyvinyl acetate based adhesive. A suitable adhesive for the lapped joint 26 is a product of L.D. Davis Industries Inc., sold under the trademark Product No. 259. It is important, during formation of the gypsum board, that the gypsum core slurry be of a uniform consistency which results in a minimum but sufficient penetration of the core slurry into the composite facings, to provide thorough adhesion of the facings to the core without any substantial bleed-through of the core mix to the outer surface of the composite facings. The above described gypsum board, produced by the method steps as described above, has outstanding resistance to deterioration by water that may penetrate through a layer of ceramic tile applied thereto using resin reinforced mortar, in addition to having superior bond between the ceramic tile and the gypsum board 10. Fig. 4 shows a wet area wall 36, with ceramic tiles 38 bonded to a gypsum board 10, with a resin reinforced Portland cement mortar 40. The resin reinforced Portland cement mortar 40 was made incorporating a resin which is similar to the resin of the gypsum board film 32, both preferably being acrylic resins.

Claims: A gypsum board, for use in wet areas for application thereto of ceramic tile, said board comprising a set gypsum core (20), front face (12) with facing material (22) thereon and a back face (16) with facing material (24) thereon, said facing material on at least said front face being a mineral fiber laminated composite facing (28,30), said composite facing including two plies, said two plies being a woven mineral fiber scrim (28) adhered to said gypsum core and a nonwoven mineral fiber mat (30) disposed outward of said scrim, said fiber mat on said front face having on its side not adhering to the scrim (28) a film (32) derived from a water-based latex, the material of said film extending through said laminated composite facing into said gypsum core. A gypsum board as defined in claim 1, wherein said mineral fiber is glass fiber. A gypsum board as defined in claim 2, wherein said facing material on both said faces is said glass fiber laminated composite facing. A gypsum board as defined in any one of claims 1 to 3, wherein said mineral fiber laminated composite facing on said back face (16) extends around side edges (14) on said board and onto said front face (12) whereat said front face laminated composite facing and said back face laminated composite facing form lapped joints (26). A gypsum board as defined in claim 4, wherein said back face laminated composite facing includes said two plies only on said back face (16) with only said unwoven mineral fiber mat (30) ply extending around said side edges (14) and onto said front face (12). A gypsum board as defined in any one of claims 1 to 5, wherein said gypsum core contains a minor percentage of water repellent chemicals. A gypsum board as defined in any one of claims 1 to 6, wherein said front face film is an acrylic film. A gypsum board as defined in claim 7, wherein said film is formed of a resin which is specifically formulated for use as a Portland cement additive. A wet area wall structure comprising a gypsum board as defined in any one of claims 1 to 8 and a plurality of ceramic tiles adhered to the front face of said gypsum board by a layer of resin reinforced mortar. A wet area wall structure as defined in claim 9, wherein the resin of said film (32) of the gypsum board is a resin similar to the resin of said mortar. The method of making a gypsum board for use in wet areas comprising the steps of laminating a ply of glass fiber scrim to a ply of a nonwoven glass fiber mat, forming a gypsum slurry containing water repellent additives into board form with said laminated glass fiber composite forming a front face facing for said gypsum board, bonding said glass fiber composite to said gypsum core by causing said gypsum slurry to penetrate into said glass fiber scrim ply of said glass fiber composite, allowing said gypsum slurry to partially set, applying a resin film to the mat on said front face, on the side of the mat not adhering to the scrim, so that the resin penetrates through said face into the partially set gypsum board, and optionally severing said coated gypsum board into predetermined lengths, and drying said gypsum board or boards. The method of claim 11, wherein said gypsum board is formed with said laminated glass fiber composite forming the facings of said gypsum board on both a front side and a back side of said gypsum board. The method of claim 12, wherein said laminated glass fiber composite on said gypsum board back side has side edge portions of solely said non-woven glass fiber mat, said side edge portions being folded over each side edge of said gypsum core and extending to said front side and adjoined to said laminated glass fiber composite on said front side. The method of any one of claims 11 to 13, wherein said resin film consists of a resin specifically formulated for use as a Portland cement additive, said resin advantageously being an acrylic resin. The use on a front face of a gypsum board - said gypsum board comprising a set gypsum core, a front face with facing material thereon and a back face with facing material thereon, said facing material on at least said front face being a mineral fiber laminated composite facing, said composite facing including two plies, said two plies being a woven mineral fiber scrim adhered to said gypsum core and a nonwoven mineral fiber mat disposed outward of said scrim - of a film derived from a water-based latex, said film being applied on the side of the nonwoven mineral fiber mat not adhering to the scrim, the material of said film extending through said facing into said gypsum core, to enhance the bonding of the board to a ceramic tile.

Inventors: BURKARD EDWARD ARTHUR, BURKARD, EDWARD ARTHUR
Applicants: NAT GYPSUM CO, NATIONAL GYPSUM COMPANY
Application year: 1990
Main classification: B32B13
IPC codes: B32B13, E04C2