Process for preparing gypsum board

Claim 1

A process for making a compressed gypsum board having exposed gypsum surfaces, which comprises: forming an aqueous slurry consisting essentially of water, setting retardant for calcined gypsum, cellulosic fibers, asbestos fibers and calcined gypsum, said slurry containing, on a water-free basis, from 0.5 to 30 weight percent of said cellulosic fibers, from 0.5 to 30 weight percent of asbestos fibers and from 60 to 95 weight percent of calcined gypsum; continuously depositing at least one layer of said slurry directly onto a moving porous surface capable of passing drainable water therethrough and retaining the solids, thereon, and draining water from said layer while same is on said surface, then removing said layer from said surface and obtaining an intermediate gypsum board product having exposed gypsum surfaces free of covering layers and containing sufficient water adhering to the surfaces of the solids to cure the gypsum; pressure molding said intermediate gypsum board product under a molding pressure of from 10 to 400 kg/cm 2 to obtain a second intermediate compressed board product; then drying said second intermediate compressed board product to obtain a final gypsum board product.