Gypsum board is a flat panel made from a core of gypsum plaster sandwiched between two sheets of heavy paper or fiberglass matting. It’s the standard material used to build interior walls and ceilings in homes and commercial buildings across North America. You’ll also hear it called drywall, wallboard, plasterboard, or by brand names like Sheetrock. A typical panel is 4 feet wide, comes in lengths from 7 to 14 feet, and weighs about 2.2 pounds per square foot in the common 5/8-inch thickness.
What Gypsum Board Is Made Of
The core of every gypsum board panel is calcium sulfate dihydrate, a naturally occurring mineral with the chemical formula CaSO₄·2H₂O. That “dihydrate” part is important: about 21% of gypsum’s weight is chemically bound water. When exposed to fire, this water is slowly released as steam, which is one reason gypsum board provides meaningful fire resistance even in its standard form.
During manufacturing, raw gypsum rock is crushed, ground, and heated to around 100–130°C in a process called calcination. This drives off most of the bound water, converting the mineral into calcium sulfate hemihydrate, commonly known as plaster of Paris. That powder is then mixed with water and additives, spread onto a moving sheet of paper, and topped with a second sheet. As the slurry sets over 40 to 60 minutes, the hemihydrate reabsorbs water and recrystallizes back into solid gypsum dihydrate, forming a rigid core bonded tightly to the paper facings.
Not all gypsum comes from quarries. Global production of synthetic gypsum from flue gas desulfurization (a process that scrubs sulfur dioxide from power plant emissions) reached an estimated 255 million tons in 2020. Roughly 75% of that synthetic gypsum goes into cement, concrete, and gypsum board manufacturing, giving the construction industry a way to turn industrial waste into building materials.
Common Types
Standard gypsum board in 1/2-inch thickness is what you’ll find on most residential walls. It’s lightweight, easy to cut with a utility knife, and suitable for rooms with normal conditions. But several specialty versions exist for situations where standard panels fall short.
- Type X (fire-resistant): A 5/8-inch panel with glass fibers and other additives in the core that help it hold together longer during a fire. Building codes require it in garages, furnace rooms, and shared walls between apartments or townhouses.
- Moisture and mold-resistant: These panels use a treated core paired with either moisture-resistant paper facers or fiberglass mat facings that won’t support mold growth. They’re designed for bathrooms, kitchens, laundry rooms, and basements. Available in standard, Type C, and Type X core formulations.
- Impact and abuse-resistant: Built with a denser core or reinforced facings to withstand dents and dings, these are common in hallways, schools, hospitals, and other high-traffic areas.
- Exterior sheathing: Fiberglass-faced panels designed to handle weather exposure during construction, used as a substrate beneath exterior cladding.
How It Replaced Plaster and Lath
Before gypsum board existed, interior walls were built by nailing thin strips of wood (lath) to the framing and then applying multiple coats of wet plaster by hand. Each coat needed days to dry before the next could be applied, and the process required skilled tradespeople. A single room could take a week or more to finish.
In 1894, Augustine Sackett patented what he called Sackett Board: a rigid panel of gypsum plaster sandwiched between two thick sheets of paper. It was soft enough to accept nails, tough enough not to crack during installation, and could cover a wall in a single day. Sackett also invented the specialized machinery to produce it at scale. The product was refined over the following decades for better strength, lighter weight, and improved fire resistance, but it remained a niche material for years. Wartime lumber rationing in the 1940s finally pushed builders to adopt drywall widely, and it has been the dominant wall-finishing method ever since.
Standard Sizes and Weight
Gypsum board comes in a few standard thicknesses. The most common for residential walls is 1/2 inch (12.7 mm). For ceilings and fire-rated assemblies, 5/8 inch (15.9 mm) is the norm. Thinner 1/4-inch and 3/8-inch panels exist for curved surfaces and overlay work, but they’re less common.
Panels are universally 4 feet wide. Lengths of 8 feet are standard for homes with 8-foot ceilings, but sheets come in lengths up to 14 feet for taller walls or horizontal installations that minimize joints. A 4-by-8-foot sheet of 5/8-inch Type X board weighs roughly 70 pounds, which matters when you’re carrying it up stairs or holding it against a ceiling.
Installation Basics
Gypsum board is fastened directly to wood or metal framing with screws or nails. Screws are the modern standard, spaced 12 inches apart for both 1/2-inch and 5/8-inch panels. Nails require closer spacing: 8 inches apart on vertical installations, and 7 to 12 inches on horizontal runs depending on panel thickness. Fasteners should sit no closer than 3/8 inch from the edge of a panel and no more than 1 inch in from the edge.
The goal when driving screws is to set the head just below the paper surface without breaking through it. A torn paper facing weakens the connection. Once panels are up, joints between sheets are covered with paper or fiberglass mesh tape and multiple thin coats of joint compound, then sanded smooth. This finishing step is what creates the seamless look of a painted wall.
Panels can be hung horizontally or vertically. On walls with framing spaced 24 inches apart, 1/2-inch board must be installed perpendicular to the framing members (horizontally) to maintain adequate support between studs.
Health Concerns With Dust
Cutting and especially sanding gypsum board generates fine dust that irritates the eyes, nose, throat, and airways. Joint compound, which is the material sanded at seams, contains a mix of ingredients including talc, calcite, mica, gypsum, and in some products, crystalline silica. Over time, repeated exposure to this dust can cause persistent coughing, phlegm production, and breathing difficulties similar to asthma. When silica is present, there’s an added risk of silicosis and lung cancer with prolonged exposure.
Wet sanding, which uses a damp sponge instead of sandpaper, dramatically reduces airborne dust and is recommended by manufacturers and safety agencies alike. When dry sanding is necessary, a properly fitted respirator and adequate ventilation are essential. Dust masks worn loosely or without proper fit testing offer limited protection.
Environmental Footprint
Gypsum board is one of the more recyclable construction materials. Scrap panels can be ground up, and the gypsum core can be recalcined and reformed into new boards. The use of synthetic gypsum from power plant emissions further reduces the need for mining virgin rock. Researchers are also exploring ways to react synthetic gypsum with carbon dioxide from flue gases, converting it into calcium carbonate. This approach captures CO₂ in a stable solid form while producing a material that can be used as filler in new gypsum panels, potentially turning two waste streams into useful products.