Drywall is composed of gypsum plaster pressed between a paper lining. The key material is gypsum (calcium sulfate), which is available in different hydration levels, and in anhydrous form. Natural gypsum stone is calcium sulfate-dihydrate (CaSO4*2H2O). The anhydrous calcium sulfate can be found in nature as anhydrite (CaSO4). Gypsum also occurs in large quantities as the industry by-product, otherwise known as flue-gas desulphurized (FGD) gypsum. There are not significant differences in the composition of finished drywall products made using these different source materials, but natural gypsum is preferred over FGD gypsum because the FGD drywall production process can release mercury into the environment. In 2018, production of synthetic gypsum surpassed production of natural gypsum in the U.S. The amount of FGD and natural gypsum used in drywall varies regionally. Products tend to be composed primarily of one type or the other. Boards can also contain around 1-10% recycled scraps from the drywall manufacturing process and drywall installation or demolition. This common product profile characterizes a type X drywall product made with FGD gypsum. Type X drywall is fire rated drywall that is more fire resistant than standard drywall. It is specified in many building codes for use in a variety of commercial and residential applications. Examples include interior and exterior walls near furnaces and utility rooms, and in the walls and ceilings of attached garages adjacent to the main living area. It has greater thickness and special core additives (mainly vermiculite and fiberglass) which provide additional fire resistance, higher rigidity, and enhanced sound attenuation as compared to regular 1/2” gypsum board. 5/8” (16mm) type X North American gypsum boards are manufactured to ASTM C1396, Standard Specification for Gypsum Board.

A historical version of this Common Product can be found here: https://pharosproject.net/common-products/2204418