Building Boards with Increased Surface Strength

Abstract

Disclosed is a building board construction with increased surface strength. More specifically, increased nail pull strength is achieved via the application of an external surface coating. The surface coating is ideally applied to a paper faced gypsum building board. In one possible embodiment, the coating is formed from a water soluble polymer.

1 . A composite building board with enhanced nail pull strength, the composite building board comprising:
 first and second liners, the first liner having an exterior face forming a decorative outer face of the building board;   a set plaster core positioned between and bonded with the first and second liners, the set plaster core formed from a cementitious slurry of predominantly calcium sulfate hemi-hydrate, the set plaster core being formed with a plurality of internal voids, the internal voids functioning to decrease the overall weight of the building board;   a polymer based coating applied to the decorative outer face of the building board wherein the coating comprises less than 10 grams per square foot of polymer.   
     
     
         2 . The composite building board as described in  claim 1  wherein the coating comprises less than 5 grams per square foot of polymer and the nail pull strength is greater than 10% higher than the uncoated building board. 
     
     
         3 . The composite building board as described in  claim 2  wherein the coating polymer comprises a synthetic polymer. 
     
     
         4 . The composite building board as described in  claim 2  wherein the coating polymer comprises a polymer selected from acrylics and acrylic copolymers, vinyl acetate polymers and copolymers, styrene-butadiene polymers and copolymers, or polyvinyl alcohols. 
     
     
         5 . The composite building board of  claim 2  wherein the coating polymer comprises one of the following:
 a copolymer containing vinyl acetate and ethylene; 
 a copolymer containing styrene and butadiene; or a poly vinyl alcohol. 
 
     
     
         6 . The composite building board of  claim 5  wherein the coating is less than 100 microns thick. 
     
     
         7 . The building board as described in  claim 3  wherein the coating polymer has a glass transition temperature below 30 degrees Celsius. 
     
     
         8 . The building board as described in  claim 3  wherein the coating polymer has a glass transition temperature above 5 degrees Celsius and below 25 degrees Celsius. 
     
     
         9 . The building board as described in  claim 1  wherein the coating polymer comprises one of the following:
 a copolymer containing vinyl acetate and ethylene; 
 a copolymer containing styrene and butadiene; 
 or a poly vinyl alcohol. 
 
     
     
         10 . The composite building board of  claim 9  wherein the coating is less than 100 microns thick. 
     
     
         11 . The composite building board of  claim 3  wherein the coating is less than 100 microns thick. 
     
     
         12 . The building board as described in  claim 11  wherein the coating is less than 50 microns thick. 
     
     
         13 . The composite building board of  claim 3  wherein the coating polymer has a tensile modulus above 500 psi and an elongation at break of greater than 500% at room temperature. 
     
     
         14 . The building board as described in  claim 13  wherein the coating polymer has an elongation at break of between approximately 500% and 10,000%. 
     
     
         15 . The building board as described in  claim 14  wherein the coating polymer has a tensile modulus between approximately 500 psi and 10,000 psi. 
     
     
         16 . The building board as described in  claim 15  wherein the coating polymer further comprises at least one of the following:
 a copolymer containing vinyl acetate and ethylene; 
 a copolymer containing styrene and butadiene; 
 or a poly vinyl alcohol. 
 
     
     
         17 . The building board as described in  claim 16  wherein the coating is less than 100 microns thick. 
     
     
         18 . The building board as described in  claim 2  wherein the coating is an aqueous solution. 
     
     
         19 . The building board as described in  claim 2  wherein the coating is an aqueous dispersion. 
     
     
         20 . The building board as described in  claim 19  wherein the coating has a percent solids between 10% and 60%. 
     
     
         21 . The building board as described in  claim 20  wherein the coating has a viscosity between 25 and 2000 centipoise. 
     
     
         22 . The building board as described in  claim 21  wherein the coating is applied by spray coating. 
     
     
         23 . The building board as described in  claim 22  wherein the coating polymer comprises one of the following:
 a copolymer containing vinyl acetate and ethylene; 
 a copolymer containing styrene and butadiene; 
 or a poly vinyl alcohol. 
 
     
     
         24 . The building board as described in  claim 23  wherein the coating is less than 100 microns thick. 
     
     
         25 . The building board as described in  claim 2  wherein the coating is not uniform across the width of the board. 
     
     
         26 . The building board as described in  claim 25  wherein the coating is more than 20% thicker in the center of the board than at the edges. 
     
     
         27 . The building board as described in  claim 26  wherein the coating polymer comprises one of the following:
 a copolymer containing vinyl acetate and ethylene; 
 a copolymer containing styrene and butadiene; 
 or a poly vinyl alcohol. 
 
     
     
         28 . The building board as described in  claim 27  wherein the coating is less than 100 microns thick. 
     
     
         29 . A composite building board with enhanced nail pull strength, the composite building board comprising:
 an exterior face forming a decorative outer face of the building board;   a set plaster core positioned beneath the exterior face, the set plaster core formed from a cementitious slurry of predominantly calcium sulfate hemi-hydrate;   a polymer based coating applied to the decorative outer face of the building board wherein the coating comprises less than 10 grams per square foot of polymer.   
     
     
         30 . The composite building board as described in  claim 1  wherein the first and second liners are formed from paper.