Abstract: A thin, circular mixing apparatus for receiving from separate sources (1) dry calcined gypsum powder and (2) the liquid ingredients of the core of a gypsum wallboard, with the liquids being fed to a small diameter radially inward centrifugal pump portion, the dry ingredients being fed to a medium diameter circular portion into which the centrifugal pump elements continually force the liquids in an outwardly spiralling path and having a radially outermost circular portion into which the mixture is further forced in a continued outwardly spiralling path and out from which the mixture is discharged, between rotating radially outwardly projecting teeth.

Abstract: A continuous calciner, particularly advantageous in converting gypsum to plaster, with two coaxial cylindrical walls, provides for heating air within the inner cylinder and then directing the air, for conveying and heating fine particles, along a spiral path, between the walls of the two coaxial cylinders, extending from one end of the calciner to an exit at the second end.

Abstract: Lightweight gypsum wallboard produced by continuously combining a small amount of surface active agent with a liquid stream which stream is made up of substantially all of the liquids to be used in the manufacture of a continuous web of gypsum wallboard, subjecting this mixture to an intense agitation with vaned saw tooth-like rotary blades in a foam generator while adding a controlled quantity of air thereto, forming a uniformly dispersed foam of very small bubbles from the liquid by completely generating all of the surface active agent therein to form this foam, and mixing this foamed liquid with finely ground dry calcined gypsum in a suitable mixing device to form a foamed settable gypsum slurry, disposing the slurry between paper cover sheets, and forming a continuous web of gypsum wallboard.

Abstract: A predecorated printed paper on the gypsum wallboard with a clear washable coating over the printed paper, and having a thin coating of polyethylene emulsion on the back paper which overcomes the tendency of the coated predecorated paper to stick to the back paper of an adjacent board when the boards are piled in stacks for storage and shipment.

Abstract: A continuous calciner, particularly advantageous in converting gypsum to plaster, with two coaxial cylindrical walls, provides for heating air within the inner cylinder and then directing the air, for conveying and heating fine particles, along a spiral path, between the walls of the two coaxial cylinders, extending from one end of the calciner to an exit at the second end.