Gypsum building product

A composition for preparing an unfaced, fire-resistant structural building material having density of at least about 60 lbs./cu. ft., flexural strength of at least about 40 lb. (1/2" thick material), and screw-holding capacity of at least about 400 lbs. comprising a substantially uniform dispersion of solids including by weight about 53% to about 78% nonfibrous calcium sulfate hemihydrate, about 7% to about 30% pulped waste paper, up to about 7% siliceous fiber, and up to about 15% ester of polyvinyl alcohol, together with a quantity of water at least about 25-fold in excess of that required to completely hydrate the calcined gypsum.

An unfaced building board capable of use as edge banding in a fire door which achieves a 1.5 hr. fire endurance rating in accordance with ASTM E-152, which board comprises by weight about 68% to about 78% set gypsum derived from calcined nonfibrous gypsum, about 7% to about 30% pulped paper fiber, up to about 15% binder polymer, up to about 7% inorganic fiber, up to about 6% clay, and up to about 6% vermiculite, said board having a density of at least about 70 lbs./cu. ft., and a screw-holding capacity of at least about 700 lb., said board having been prepared with a quantity of water at least about 25-fold that required to completely hydrate the calcined gypsum.

An unfaced building panel capable of use as facing in a hollow-core fire door which achieves a 20 min. fire endurance rating when tested in accordance with ASTM E-152, which panel comprises by weight about 75% to about 90% set gypsum derived from calcined nonfibrous gypsum, about 10% to about 14% pulped paper fiber, up to about 9% binder polymer, and about 0.8% to about 2% inorganic fiber, said board having a density of at least about 60 lbs./cu. ft., said board having been prepared with a quantity of water at least about 25-fold times that required to completely hydrate the calcined gypsum.

An unfaced, fire-resistant structural building material which includes by weight about 65% to about 90% set gypsum dihydrate derived from gypsum hemihydrate, about 7% to about 30% pulped paper fiber, and up to about 1.5% to about 35% performance booster selected from inorganic fiber, clay, vermiculite and binder polymer, said product having density of at least about 60 lbs./cu. ft., flexural strength of at least 40 lb. (1/2" thick material), and screw-holding capacity of at least about 400 lbs., said board having been prepared with a quantity of water at least about 25-fold times that required to completely hydrate the calcined gypsum.

A building material comprising by weight:

• at least about 65% set gypsum dihydrate derived substantially from gypsum hemihydrate;
• and
• paper fibers derived substantially from pulped paper, said fibers being disposed substantially homogeneously throughout said set gypsum dihydrate by mixing said pulped paper and gypsum hemihydrate with a quantity of water at least about 25-fold times that required to completely hydrate the gypsum hemihydrate.