Patent ID: RE44070

Claim:
A composite light weight gypsum composite board comprising: a foamed low density set gypsum core having a top surface and a bottom surface, the foamed low density set gypsum core made using a gypsum-containing slurry including stucco, from about 0.5% by weight to about 10% by weight pregelatinized starch based on the weight of stucco , and foam, a top non-foamed high density bonding layer having a thickness of about 2 mils to less than about 7 mils covering the top surface of the foamed low density set gypsum core, a bottom non-foamed high density bonding layer having a thickness of about 2 mils to less than about 7 mils covering the bottom surface of the foamed low density set gypsum core, the top and bottom non-foamed high density bonding layers comprising from about 10% by weight to about 16% by weight of the total amount of the gypsum-containing slurry, a top cover sheet, and a bottom cover sheet, wherein the top cover sheet is bonded to the foamed low density set gypsum core by the top non-foamed high density bonding layer, and the bottom cover sheet is bonded to the foamed low density set gypsum core by the bottom non-foamed high density bonding layer, the foamed low density set gypsum core has a density from about 10 pcf to about 27 pcf and the top and bottom non-foamed high density bonding layers have a density from about 60 pcf to about 70 pcf, and wherein the composite board has a dry weight of about 1000 lb/msf or less for a ½ inch thick board, a nail pull resistance of at least about 77 lb /msf , and a core hardness of at least about 11 lb /msf .