To produce gypsum board, 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 board 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 board is then cut to length and conveyed through dryers to remove any free moisture.
Gypsum manufacturers also rely increasingly on “synthetic” gypsum as an effective alternative to natural gypsum ore. Synthetic gypsum is a byproduct primarily from the desulfurization of the flue gases in fossil-fueled power plants. Gypsum board is an excellent fire resistive material. It is the most commonly used interior finish where fire resistance classifications are required. Its noncombustible core contains chemically combined water which, under high heat, is slowly released as steam, effectively retarding heat transfer. Even after complete calcination, when all the water has been released, it continues to act as a heat insulating barrier. In addition, tests conducted in accordance with ASTM E 84 show that gypsum board has a low flame spread index and smoke density index. When installed in combination with other materials it serves to effectively protect building elements from fire for prescribed time periods.
Developed through modern technology as a result of specific requirements, gypsum board is mainly used as the surface layer of interior walls and ceilings; as a base for ceramic, plastic, and metal tile; for exterior soffits; for elevator and other shaft enclosures; as area separation walls between occupancies; and to provide fire protection to structural elements. Most gypsum board is available with aluminum foil backing which provides an effective vapor retarder for exterior walls when applied with the foil surface against the framing.
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