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WHAT IS GYPSUM BOARD?
 

Gypsum board is the generic name for a family of panel products that consist of a noncombustible core, composed primarily of gypsum, and a paper surfacing on the face, back and long edges. Gypsum board is one of several building materials covered by the umbrella term “gypsum panel products.” All gypsum panel products contain gypsum cores; however, they can be faced with a variety of different materials, including paper and fiberglass mats.

Gypsum board is often called drywall, wallboard, or plasterboard. It differs from other panel-type building products, such as plywood, hardboard, and fiberboard, because of its noncombustible core and paper facers. When joints and fastener heads are covered with a joint compound system, gypsum wall board creates a continuous surface suitable for most types of interior decoration. A typical board application is shown in Figure 1.

Figure 1

Fig. 1 – Horizontally Applied Gypsum Wallboard Showing Joints and Framing

Gypsum is a mineral found in sedimentary rock formations in a crystalline form known as calcium sulfate dihydrate CaSO4•2H2O. One hundred pounds of gypsum rock contains approximately 21 pounds (or 10 quarts) of chemically combined water. Gypsum rock is mined or quarried and transported to the manufacturing facility.

The manufacturer receives quarried gypsum, and crushes the large pieces before any further processing takes place. Crushed rock is then ground into a fine powder and heated to about 350 degrees F, driving off three-fourths of the chemically combined water in a process called calcining. The calcined gypsum (or hemihydrate) CaSO4•½H2O is then used as the base for gypsum plaster, gypsum board and other gypsum products.

Synthetic gypsum, commonly known as the FGD (Flue Gas Desulphurization) gypsum or DSG (desulphurised) gypsum may also be used in the production of gypsum board. This product is primarily derived from coal-fired electrical utilities which have systems in place to remove sulfur dioxide from flue gasses. These systems capture the sulfur dioxide by passing the gasses through scrubbers that contain limestone (calcium carbonate) which absorbs and chemically combines with the sulfur dioxide to form pure calcium sulfate, or gypsum. The synthetic gypsum is then transported to the gypsum board manufacturer; the production process for calcining synthetic gypsum is largely the same as with mined gypsum only no primary crushing is necessary.

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, chemically combining with the water that was removed during calcination and reverts 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.


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