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Gypsum drywall is the name for a family of panel-type products consisting of a noncombustible core, primarily of gypsum, with a paper surfacing on the face, back, and long edges.

Gypsum drywall is often called board, wallboard, or plasterboard and differs from products such as plywood, hardboard, and fiberboard, because of its noncombustible core. It is designed to provide a monolithic surface when joints and fastener heads are covered with a joint treatment system.

Gypsum is a mineral found in sedimentary rock formations in a crystalline form known as calcium sulfate dihydrate. One hundred pounds of gypsum rock contains approximately 21 pounds (or 10 quarts) of chemically combined water. Gypsum rock is mined or quarried and then crushed. The crushed rock is then ground into a fine powder and heated to about 350 degrees Fahrenheit, driving off three fourths of the chemically combined water in a process called calcining. The calcined gypsum is then used as the base for gypsum plaster, gypsum drywall and other gypsum products.

To produce gypsum drywall, the calcined gypsum is mixed with water and additives to form a slurry which is fed between continuous layers of paper on a board machine. As the drywall moves down a conveyer line, the calcium sulfate recrystallizes or rehydrates, reverting to its original rock state. The paper becomes chemically and mechanically bonded to the core. The drywall is then cut to length and conveyed through dryers to remove any free moisture.

Gypsum drywall manufacturers also rely increasingly on “synthetic” gypsum as an equivalent alternative to natural gypsum ore. The former is a by-product, from other manufacturing processes, primarily the desulphurization of flue gases in fossil-fueled power plants. These power-generating facilities supply a steady stream of “by-product synthetic gypsum” to nearby gypsum drywall manufacturing facilities.