Abstract: A method for producing a lightweight set cementitious product having excellent strength by forming a aqueous cementitious slurry, incorporating therein expandable polystyrene beads which are less than completely expanded, and heating the slurry to drive off excess water, to cause a cementitious mixture to set, and to further and completely expand the polystyrene beads. In a preferred embodiment and aqueous slurry of calcium sulfate hemihydrate is produced including expandable polystyrene beads in a state which they are partially but not fully pre-expanded. The slurry is deposited between two paper cover sheets, and the product is heated to drive off excess water, to set the gypsum to the solid dihydrate state, and to complete the expansion of the polystyrene beads until they reach their fully expanded state, thereby resulting in a strong lightweight gypsum wallboard which has excellent adhesion between the expanded polystyrene beads and the set gypsum.

Abstract: Hydrodynamic pumping of the fluidized calcining mass in a kettle is set up by the continuous flow of the mass to and from heating rods immersed therein which are constantly emitting at least about 1 British Thermal Unit of heat per minute per square inch of the surface of the rods. The transfer of heat from the walls and bottom of the kettle is enhanced so that more of the available heat is actually absorbed than in a kettle lacking such heating rods. The rate of calcination may be increased while the rate of heat input is decreased.

Abstract: Gypsum is calcined by contacting it with the hot gases spewing out of a combustion tube submerged in the mass of gypsum. The formation of dead-burned anhydrite is reduced by surrounding the combustion tube with a second tube called a draft tube. Gypsum passing through the annulus between the tubes is heated by the hot gases and is ejected from the annulus to prevent repeated excursions into the hot gas zone at the muzzle of the combustion tube.

Abstract: Gypsum is calcined by contacting it with the hot gases spewing out of a combustion tube submerged in the mass of gypsum. The formation of dead-burned anhydrite is reduced by surrounding the combustion tube with a second tube called a draft tube. Gypsum passing through the annulus between the tubes is heated by the hot gases and is ejected from the annulus to prevent repeated excursions into the hot gas zone at the muzzle of the combustion tube.

Abstract: A process for producing a healed stucco of low water demand is disclosed in which calcined gypsum is treated with an aqueous solution of a gypsum solubilizing agent, preferably in an impacting blender while grinding the calcined gypsum to increase its surface area. The product can be dried for storage or sent directly to forming gypsum board.

Abstract: A process for preparing calcined gypsum (stucco) which comprises treating a mass of calcined gypsum by adding, with thorough blending, small portions of an aqueous solution of ligno sulfonate; allowing the treated stucco to heal; and optionally drying the healed stucco and further optionally grinding the healed stucco. If the treated calcined gypsum is not to be used shortly after the healing procedure, it should be dried to provide storage stability. If further strength is desired the treated stucco should be ground to expose fresh crystal faces. The process is particularly useful in gypsum board manufacture and production of bagged building and industrial plasters.