Abstract: Expanded perlite coated with a composition to render the perlite impervious to water, and a joint compound incorporating the same. The perlite is ground prior to expansion to provide subsequently expanded perlite having a mean particle size from about from about 50 to about 70 microns, the joint compound formed from the perlite having greater uniformity in paint gloss appearance between the painted surface of the joint compound and the painted surface of the gypsum wallboard on which the joint compound is applied.

Abstract: Disclosed is a gypsum board having a kerfed edge along substantially the full length of at least one edge wherein the kerf has sidewalls inclined opposingly inwardly toward one another but do not intersect and are joined by a bottom surface of uneven profile characterized by alternately and irregularly spaced projections and depressions. The uneven bottom surface and each sidewall meet at a jagged intersection. Said kerfed edge provides enhanced strength in a direction perpendicular to the sidewalls providing improved board retention by flanged supports over that of conventional mechanically sawn kerfed edge boards. A process for providing kerfed edge gypsum board is also disclosed which comprises projecting into the board edge a first and second fine stream of aqueous liquid which incline toward one another at angles of incidence to a line perpendicular to the board edge which provides a combined angle therebetween of from about 3.degree. to about 20.degree..