Gypsum wallboard produced using a high water-to-stucco ratio

Abstract

A gypsum composition, board, and method of producing a gypsum board with increased fire endurance are described. The set gypsum-containing composition can be used to prepare a gypsum board having fire endurance, based on particular water-to-stucco ratios.

We claim: 
     
         1 . A fire resistant gypsum board comprising:
 a set gypsum composition disposed between two cover sheets, the set gypsum composition comprising an interlocking matrix of set gypsum formed from a slurry comprising at least stucco and water;   the slurry having a water-to-stucco ratio from about 0.7 to about 2.0; and   the board having a density from about 24 lbs/ft 3  to about 40 lbs/ft 3 , and when at a thickness of about ⅝ inch, a nail pull resistance of at least about 70 lbs of force as determined according to ASTM C473-09, and a Fire Endurance Index (FEI) greater than about 52 minutes.   
     
     
         2 . The fire resistant gypsum board of  claim 1 , wherein the set gypsum composition comprises gelatinized starch in an amount greater than about 1% by weight based on the weight of the stucco. 
     
     
         3 . The fire resistant gypsum board of  claim 1 , wherein the set gypsum composition comprises a thickener. 
     
     
         4 . The fire resistant gypsum board of  claim 3 , wherein the thickener is silica fume, Portland cement, fly ash, clay, fine cellulosic particles, or a high molecular weight polymer, or any mixture thereof. 
     
     
         5 . The fire resistant gypsum board of  claim 4 , wherein the thickener is less than about 10% by weight based on the weight of the stucco. 
     
     
         6 . The fire resistant gypsum board of  claim 4 , wherein the high molecular weight polymer is polyacrylamide. 
     
     
         7 . The fire resistant gypsum board of  claim 1 , wherein the composition further comprises high thermal expansion particles. 
     
     
         8 . The fire resistant gypsum board of  claim 7 , wherein the high thermal expansion particles are vermiculite. 
     
     
         9 . The fire resistant gypsum board of  claim 8 , wherein vermiculite is less than about 5% by weight based on the weight of the stucco. 
     
     
         10 . The fire resistant gypsum board of  claim 1 , wherein the gypsum board has a board density from about 24 lbs/ft 3  to about 33 lbs/ft 3 . 
     
     
         11 . The fire resistant gypsum board of  claim 1 , wherein the gypsum board has a thickness from about 0.25 inches to about 1.0 inches. 
     
     
         12 . The fire resistant gypsum board of  claim 1 , wherein the gypsum board has a thickness from about 0.59 inches to about 0.65 inches. 
     
     
         13 . The fire resistant gypsum board of  claim 1 , wherein the gypsum board has a Fire Endurance Index (FEI) at least 3 minutes greater than a board comprising set gypsum formed with a water-to-stucco ratio of less than about 0.7. 
     
     
         14 . The fire resistant gypsum board of  claim 1 , wherein the gypsum board has a Fire Endurance Index (FEI) at least 4 minutes greater than a board comprising set gypsum formed with a water-to-stucco ratio of less than about 0.7. 
     
     
         15 . The fire resistant gypsum board of  claim 1 , wherein when the board is built into a test assembly in accordance with UL U305, the board has a fire rating of at least about 55 minutes when heated in accordance with the time-temperature curve of ASTM standard E119-09. 
     
     
         16 . The fire resistant gypsum board of  claim 1 , wherein the board is built into a test assembly in accordance to UL U305, and has a fire rating of at least about 60 minutes when heated in accordance with the time-temperature curve of ASTM standard E119-09. 
     
     
         17 . The fire resistant gypsum board of  claim 1 , wherein when the board is built into a test assembly in accordance with UL U419, the board has a fire rating of at least about 60 minutes when heated in accordance with the time-temperature curve of ASTM standard E119-09. 
     
     
         18 . A fire resistant gypsum board comprising:
 a set gypsum composition disposed between two cover sheets, the set gypsum composition comprising an interlocking matrix of set gypsum formed from a slurry comprising at least stucco and water;   the slurry having a water-to-stucco ratio from about 1.2 to about 2.0;   the board having a density from about 24 lbs/ft 3  to about 40 lbs/ft 3 , and when at a thickness of about % inch, a nail pull resistance of at least about 70 lbs of force as determined according to ASTM C473-09, and a Fire Endurance Index (FEI) greater than about 54 minutes.   
     
     
         19 . A method for making a fire resistant gypsum board comprising:
 forming a mixture of at least stucco and water,   disposing the slurry on a first sheet,   disposing a second sheet on the slurry to form a board preform having two cover sheets,   cutting the board preform into a board of predetermined dimensions after the slurry has hardened sufficiently for cutting, and   drying the board;   the slurry having a water-to-stucco ratio from about 0.7 to about 2.0;   the board when dried having a density from about 24 lbs/ft 3  to about 40 lbs/ft 3 , and when at a thickness of about % inch, a nail pull resistance of at least about 70 lbs of force as determined according to ASTM C473-09, and a Fire Endurance Index (FEI) greater than about 52 minutes.   
     
     
         20 . The method of  claim 19 , wherein the water-to-stucco ratio is from about 1.2 to about 2.0.