What Is Drywall Made Of?

Drywall is the building material used to create many walls in homes and commercial spaces as a cheap and easy replacement for troweling plaster. Its familiar panels of white rock-like material are covered with paper and are the most popular wall covering for residential use. However, cutting and installing it requires a safety mask to prevent breathing its potentially harmful fine dust.

Drywall was invented in 1916 by the U.S. Gypsum Company. Earlier forms of the product, plasterboard, were manufactured as early as 1888 in Kent, England. The U.S. Gypsum company created the product with wrapped paper edges and gave it the now-familiar name of Sheetrock.

Initially, the product was only mildly successful, as most builders continued to prefer traditional plaster wall construction. But after World War II, when hundreds of thousands of homes were swiftly built in the boomer economy of the late 1940s and 1950s, drywall became the standard for residential wall construction. Hanging drywall is the most popular way to finish wall surfaces.

What Is Drywall Made Of?

Drywall is made of gypsum plaster and cellulose or fiberglass as its main ingredients. Drywall panels, also known as wallboard, plasterboard, gypsum board, or Sheetrock, are created by sandwiching a core layer of wet gypsum plaster between heavy paper or fiberglass surface sheets and then hardening them in drying chambers. Once dry, the material becomes strong and rigid and is ready to use as a building material.

Cellulose or Fiberglass

Up to 10% of drywall's composition comprises cellulose, found in the paper facing on both sides of the drywall panel.

Increasingly, though, drywall is being faced not with paper but with mold-resistant fiberglass. Examples include USG Sheetrock Mold Tough and GP's DensArmor Plus. If you ever use a fiberglass joint tape such as FibaTape, you use the same type of material for facing panels of mold-resistant drywall.

Gypsum Plaster

Comprising between 70 to 90% of sheet drywall, gypsum has long been the mainstay of drywall products. Otherwise known as calcium sulfate, gypsum is cheap to mine, is fire-proof, and provides superior sound-deadening properties. However, the layer of rock-like material in drywall panels is not pure gypsum but is more accurately known as gypsum plaster.

Fire-rated type X drywall has fiberglass added to the gypsum. Unlike asbestos, known to cause an often fatal illness called mesothelioma, this gypsum dust is not a grave health hazard. 

Additives

But while gypsum does indeed comprise the bulk of drywall panels, several other additives are included. This material is manufactured by first heating the raw gypsum powder to drive off the water. The material is then slightly rehydrated and mixed with various fibers and additives to improve strength, speed the hardening, hinder mildew and mold, and provide other benefits. These materials are included in only trace amounts, by volume, but they are essential to creating the gypsum plaster core of drywall panels:

• Paper or fiberglass fibers
• Plasticizers
• Starch
• Finely ground mica crystal as an accelerant
• EDTA or other chelating agents
• Anti-mildew agents, such as boric acid
• Wax emulsion or silanes hinder water absorption
• Potassium sulfate
  

What Is Joint Compound Made Of?

In addition to the large drywall panels, a wall system also depends on the joint compound, or mud, that covers the tape sealing the joints between panels. Because this compound dries to a finish that looks like gypsum, it's often assumed that the joint compound is a liquified gypsum material. It is not. Instead, the composition of drywall mud includes:

• Calcium carbonate: Otherwise known as ground limestone, it is the main mineral in drywall mud. 
• Talcum: Ultra-fine talcum powder makes sanding drywall joints such an unpleasant chore. This ultra-fine mineral, familiar in baby powder, is used in a joint compound because its plate-shaped particles lie flat and resist cracking. Talc is the element that helps your mud sand down as smooth as glass. By volume, 5% and 15% of joint compound is made up of talc.

Are There Harmful Chemicals in Drywall?

Drywall is safe when kept solid and stable. But with anything that produces dust and fine particulates, installers must wear protective equipment to prevent breathing in drywall dust. The fine dust contains known carcinogens like formaldehyde, acetaldehyde, and crystalline silica. When inhaled, these contents can be harmful.

Publicity surrounding unsafe drywall mainly concerns hazardous chemicals in drywall panels manufactured in China. For example, sulfur has been found in Chinese drywall but not in most U.S.-made drywall. An excessive level of sulfur in drywall has been linked to corrosion of electrical wiring and plumbing pipes.

Strontium has been found in both Chinese drywall and U.S.-made drywall, although the concentrations are much higher in Chinese products. Some drywall products also contain various agents to fight mold and mildew, and these agents can cause difficulty for sensitive individuals.