To produce gypsum board, 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.
ASTM standards govern the manufacture of gypsum board and set strict criteria for strength, water resistance, and other characteristics.