Drywall, also known as wallboard, plasterboard, and Sheetrock®, is a wall building material used in the construction trade worldwide. It consists of a large sheet of gypsum plasterboard that is typically up to a half-inch thick (about 1 cm), and which is often cut into four by eight foot panels (about 1.2 meter by 2.4 meeter). A thick, durable paper, called drywall paper, lines both sides. Drywall paper is necessary to maintain the gypsum plasterboard’s integrity, preventing it from chipping or even crumbling when nailed, or while being moved or installed. Drywall paper can be up to 1/32 of inch thick (about 1 millimeter), making it rather easy to repair should minor blemishes appear on its surface.
On standard drywall, drywall paper is typically white and smooth on the outward facing side, and rough and grayish on the side that meets framing studs. A second type of drywall, called Greenboard due to the greenish hue of its drywall paper backing, is water and mold resistant. This product is often used in bathrooms and other areas of high humidity. Although all drywall is naturally fire resistant due to the moisture content in processed gypsum, a third variety of drywall contains fiberglass or other fire resistant additives, allowing it to be labeled and sold as "fire resistant." The drywall paper on all three varieties is typically recycled.
As the name suggests, drywall replaced wet plaster wall construction and came into widespread use after WWII, when builders sought out less expensive and more streamlined methods of construction. Prior to the invention of drywall, builders formed walls by applying wet plaster to thin boards called laths, which were nailed to framing studs. This process required considerable attention to detail and some degree of skill, rendering it both impractical and expensive when compared to forming walls with drywall.
The United States Gypsum Company, formed in 1901, made the first gypsum panel from a naturally occurring mineral called calcium sulfate dehydrate. The processed mineral, called gypsum calcine, is mixed with water to form a slurry and then poured between sheets of drywall paper. After being kiln-dried, the hardened drywall is cut into desired lengths and sizes.
Some problems requiring repair to drywall and drywall paper include nails that emerge through the surface of the drywall paper, and indentations or holes resulting from trauma to the wall. Bumps and minor blemishes are often fixed quickly and easily by repositioning the nail, applying joint compound over the nail head, and then sanding and re-painting. For larger indentations or small holes, the same filling, sanding and painting process is used.