Light weight gypsum board

Abstract

The invention generally provides gypsum-containing slurries including stucco, naphthalenesulfonate dispersant, and pregelatinized starch. The naphthalenesulfonate dispersant is present in an amount of about 0.1%-3.0% by weight based on the weight of dry stucco. The pregelatinized starch is present in an amount of at least about 0.5% by weight up to about 10% by weight of pregelatinized starch by weight based on the weight of dry stucco in the formulation. Other slurry additives can include trimetaphosphate salts, accelerators, binders, paper fiber, glass fiber, and other known ingredients. The invention also comprises the gypsum-containing products made with such slurries, for example, gypsum wallboard, and a method of making gypsum wallboard.

1 - 19 . (canceled) 
     
     
         20 . A light weight gypsum board comprising:
 a set gypsum composition disposed between two cover sheets, the set gypsum composition formed from at least water, stucco, starch, dispersant, and polyphosphate;   the stucco is in an amount of at least about 700 lb/MSF;   the starch is in an amount from about 0.5% to about 10% by weight based on the weight of the stucco and is effective to increase the core hardness of the gypsum composition relative to the gypsum composition without the starch;   the dispersant is in an amount from about 0.1% to about 3.0% by weight based on the weight of the stucco;   the polyphosphate is in an amount from about 0.12% to about 0.4% by weight based on the weight of the stucco;   the board has a density of about 34 lb/ft 3  or less; and   the board has a core hardness of at least about 11 lb, the core hardness determined according to ASTM standard C473.   
     
     
         21 - 30 . (canceled)