If your house was built in the last 50 years or so, there's a very good chance that all of the walls and ceilings are covered with drywall. Drywall is essentially the modern alternative to hand-applied wall plaster and has all but replaced plaster in new home construction. When it's time to choose a material to cover the framing on your interior walls and ceilings, the low cost and relatively DIY-friendly installation of drywall make it hard to beat.
How Drywall is Made
Drywall and plaster (and plaster of Paris) share the same main ingredient: gypsum. Gypsum is a natural, nontoxic mineral that is mined in 85 countries around the world, including the U.S. Its chemical makeup consists of calcium, sulfur bound to oxygen, and water. Gypsum crystals are ground into a fine, white power that binds into a solid mass when mixed with water. In addition to mined gypsum, drywall can be made from "synthetic" gypsum derived from flue-gas desulfurization (FGD), a process of cleaning smokestacks in coal-burning power plants.
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A drywall panel consists of a gypsum core wrapped in several layers of paper (typically recycled paper). During manufacturing, a slurry of dense liquid gypsum is poured onto continuous sheets of paper. This is followed by a center layer of aerated gypsum and topped with another dense layer of gypsum before more paper is sandwiched on top. The sheets are extruded for a uniform thickness and to create a taper along the long edges. The short edges are cut to create the various lengths of panels. The front paper of the panel is called the face paper and is usually white. The back paper is usually a light brown, similar to butcher paper.
A Brief History of Drywall
Drywall was originally known as Sackett Board, after its inventor, Augustine Sackett. It was patented in 1894 and was intended as a labor-saving substitute for traditional plaster. In 1909, Sackett's invention was bought by the US Gypsum Company (USG), which remains North America's largest producer of drywall panels today.
Drywall's big break in residential construction started after WWII, when its economy and ease of installation were ideal for the building boom of the time, and its clean, flat white appearance fit the aesthetic ideals of 1950s America. Today, drywall is the predominant wall and ceiling finish material in residential construction and is used in over 96 percent of new homes.
Like many common building materials, drywall has a lot of nicknames. At the top of the list is Sheetrock, which is a brand name of drywall made by the USG company. Popular generic terms for drywall include wallboard, plasterboard, and, more technically, gypsum board and gypsum panels.
In the building trades, "drywall" is used as both a noun and a verb (Drywall it!). The tapered edges of drywall panels are called the "factory" edges, while the square-cut ends are called "butt" edges. Drywall joint compound, a gypsum-based paste used to cover the joints between panels, is known as "drywall mud" or simply "mud."
Drywall Sizes and Types
Drywall comes in 4-foot-wide panels, or sheets, and in lengths of 8 to 16 feet. The standard panel thickness for house walls and ceilings is 1/2 inch, but 1/4-inch, 3/8-inch, and 5/8-inch are also commonly available. Standard drywall is suitable for interior installation in dry locations.
Common types of specialty drywall include moisture-resistant drywall (nicknamed greenboard for its green face paper), fire-rated drywall (used on garage walls and other areas that require high fire-resistance), and flexible drywall (a thin panel for curved structures). There are also drywall products designed as backing for ceramic tile installations. These have a fiberglass or polymer facing to resist water damage if moisture gets through the tiled surface. In the past, greenboard was commonly used as a tile backer, but this is no longer considered a best practice.
Drywall is installed in two phases: hanging the panels and finishing the joints. Hanging drywall takes some muscle but little skill. Finishing drywall takes practice, patience, and, for beginners, a heavy dose of humility. But that's not to say it's for professionals only. In fact, drywalling is one of the best projects for DIYers to take on, since it is a valuable skill with lots of applications.
Drywall panels can be installed over wood or metal framing, using coarse-thread screws for wood and fine-thread screws for metal (most installers don't use nails anymore because they tend to pull out over time). Ceilings get drywalled first, followed by the walls. Panels typically are run vertically on walls (which makes finishing easier), but they can also go horizontally. Panels are butted together at the sides and ends, but it's fine if you cut one a little short; the finishing can easily cover gaps up to about 1/4 inch.
Now comes the tricky part. Drywall joints—any seam where panels come together, including the corners—must be taped with drywall joint tape. There are two types: paper tape and mesh tape. Paper tape is "glued" to the joint with a thin layer of joint compound (mud). Mesh tape is self-adhesive and gets stuck directly to the drywall face paper. All tape gets covered with at least three coats of mud, which is applied with progressively larger drywall knives (or at least a 6-inch and 10- or 12-inch knife). Corners that stick out into a room, called outside corners, can be covered with a plastic or metal angle called corner bead. This is much easier to finish and is more durable than a taped outside corner.
The first finish coat of mud seals the paper tape and begins to hide the textured surface of the mesh tape. This is applied with a 4- or 6-inch knife. The second coat, applied with a 6-inch knife, fills the recess created by the tapered edges of the panels. This recess makes it easy to apply tape and mud without creating a hump in the finished surface. Butt joints—where two square-cut ends come together—are harder to finish because they don't have this recess.
The final coat (or coats) is applied with the largest knife and is intended to spread out and smooth the joint to make it as flat as possible. The trick here is to keep the mud layer thin and smooth and to "feather" the joint onto the surrounding panel area that has no mud. When the last coat of mud has dried, all of the mud is sanded with sandpaper or a sanding screen to get the installation ready for paint. The ultimate goal is to make the joints invisible once the drywall is painted. Good luck!