The invention generally provides a light weight composite
gypsum board including a foamed
low density set
gypsum core, a top non-foamed (or reduced-foamed) bonding
high density layer and a bottom non-foamed (or reduced-foamed) bonding
high density layer, a top cover sheet bonded to the foamed
low density set
gypsum core by the top non-foamed (or reduced-foamed) bonding
high density layer, and a bottom cover sheet bonded to the foamed
low density set gypsum core by the bottom non-foamed (or reduced-foamed) bonding high density layer. The foamed low density set gypsum core and the non-foamed (or reduced-foamed) bonding high density
layers are made from a gypsum
slurry including
stucco,
pregelatinized starch present in an amount of about 0.5-10% by weight based on the weight of
stucco, preferably a
naphthalenesulfonate disperant present in an amount of about 0.1-3.0% by weight based on the weight of
stucco, and preferably
sodium trimetaphosphate present in an amount of about 0.12-0.4% by weight based on the weight of stucco. Other
slurry additives can include accelerators, binders, paper
fiber,
glass fiber, and other known ingredients. The foamed low density set gypsum core is prepared having a density of less than about 30 pcf using
soap foam in the gypsum-containing
slurry. The combination of components provide a composite gypsum board having light weight and high strength. A method of making the composite gypsum board is also provided.