Gypsum board is the premier building material for wall, ceiling, and partition systems in residential, institutional, and commercial structures. Designed to provide a monolithic surface when joints and fastener heads are covered with a joint treatment system, gypsum board’s aesthetic value is equaled in importance by its natural fire resistance properties. Gypsum, chemically known as “calcium sulfate dihydrate,” contains chemically combined water in an amount approximately 21 percent by weight.