Drywall is the quiet workhorse of modern construction. Behind almost every painted wall in a house built after 1950 sits a panel of gypsum plaster sandwiched between paper facings, a material that replaced hand-troweled plaster during the post-war housing boom because it went up faster and cost less. The panels are standard in residential and commercial building alike, yet few people think about what is inside them until a wall is damaged or a renovation exposes the framing. The composition matters for repairs too: a patch job that involves taping new drywall to existing painted drywall behaves differently from a fresh installation, because the old surface carries paint, texture, and decades of dust.
What Is Drywall Made Of?
Drywall is made from two basic components: a core of gypsum plaster and a facing of paper or fiberglass on both sides. The gypsum core supplies the mass and the fire resistance, while the facings carry the tensile loads and give joint compound something to bond to.
The Gypsum Core
Gypsum is a soft sulfate mineral that forms when seawater evaporates and leaves deposits behind. Manufacturers mine it, crush it, and heat it in a process called calcination that drives off water and turns the mineral into a powder which sets again when water is added. The powder is mixed with water, starch, and a small amount of foaming agent to form a slurry that is cast between the paper facings. Gypsum deposits are found on every continent, and the mineral is also recovered as a byproduct of coal-fired power plant scrubbers; synthetic gypsum behaves the same in drywall as the mined material and has become a major share of the supply.
Paper and Fiberglass Facings
Up to 10 percent of a drywall panel by weight is facing material. Standard panels use heavy paper on the face and a lighter paper on the back. Mold-resistant panels increasingly substitute fiberglass mats for paper, because fiberglass gives mold spores nothing to feed on.
The paper surface is not packaging. Joint compound keys into the paper fibers, which is why the preparation steps for working over previously painted drywall include scuffing the gloss and wiping away dust before any new compound goes on.
Common Drywall Types
| Panel Type | Core and Facing | Typical Use |
|---|---|---|
| Regular | Standard gypsum, paper facing | Walls and ceilings in dry areas |
| Moisture-resistant | Standard gypsum, treated paper | Bathrooms and laundry rooms |
| Mold-resistant | Fiberglass facings | Basements and humid spaces |
| Type X | Glass fibers in the core | Fire-rated walls and ceilings |
| Sound-rated | Denser core | Shared walls and media rooms |
How Panels Are Manufactured
- Gypsum rock is mined and crushed into a fine powder.
- The powder is heated to drive off water and produce a dry plaster.
- The plaster is mixed with water, starch, and additives into a slurry.
- The slurry is spread between continuous sheets of paper on a long forming table.
- The wet board travels through a drying kiln until the core sets hard.
- Panels are cut to length, bundled, and shipped to distributors.
What Is Joint Compound Made Of?
Joint compound, commonly called mud, hides the seams between panels. Its base ingredient is the same gypsum that forms the panel core, ground finer and blended with binders and water into a paste that dries hard and sands smooth.
Ingredients in Joint Compound
- Gypsum dust: the setting agent and the bulk of the mix.
- Limestone and clay: fillers that give the mud body.
- Binders: hold the dried film together.
- Water: added at the factory or on site.
- Additives: control drying time, shrinkage, and workability.
Types of Joint Compound
- All-purpose compound: the standard choice for embedding tape and filling the first coats.
- Lightweight compound: easier to sand, used for topping coats.
- Topping compound: dries harder and shrinks less, but has no adhesive strength for tape.
- Setting-type compound: hardens by chemical reaction instead of drying.
Setting-Type Compounds for One-Day Finishes
Setting compounds are sold as powders mixed with water on site. They cure in 20 to 90 minutes depending on the product, which lets a crew complete all three coats in a single day instead of waiting for each coat to dry. The trade-off is working time: once mixed, the bucket has a hard deadline.
Bags labeled all-purpose dominate retail shelves because one bucket can carry the whole job from tape embed to finish coat. Professionals often split the work, using a setting compound for the first coats and a lightweight topping for the final pass. For retrofit work, the sequence for taping new drywall to existing painted drywall starts with a bonding primer so the mud adheres to the old surface, then follows the same coat schedule used on fresh board.
Taping and Finishing Drywall Joints
Finishing is where drywall earns its reputation as skilled labor. The goal is a flat plane with no visible seams, which takes three coats of compound and a steady hand with the taping knife. The width of each coat grows with every pass: the tape coat spans about 4 inches, the second coat widens to 8, and the third reaches 12, so the finished joint feathers into the surrounding board instead of leaving a ridge.
The Three-Coat Finishing Sequence
- Embed paper or fiberglass tape in the first coat of mud along every joint.
- Let the first coat dry, then apply a second, wider coat to feather the edges.
- Apply a third, wider coat after the second dries.
- Sand between coats as needed, then prime before painting.
Tools and Tricks for Faster Finishing
Hand finishing moves at roughly 60 to 100 linear feet of joint per day for a careful taper. Fiberglass tape embeds with less shrinkage than paper and needs no water, but it shows under gloss paint unless the finish coats are built out fully. A self-mudding drywall tape dispenser removes one of the slowest steps, because the tape reaches the wall already coated with compound and the finisher only presses it down and wipes it smooth.
Hanging and Fastening Drywall Panels
Panels are screwed to the framing with drywall screws driven slightly below the paper surface without tearing it. The dimple left by the screw head is filled during finishing. Layout starts with the ceiling whenever possible, because ceiling panels support the top edge of the wall panels below; stagger the vertical seams so they do not line up across a single stud, and keep joints tight without forcing panels together.
Fastening Patterns and Screw Spacing
- Screws every 12 inches along the framing for walls, every 8 inches for ceilings.
- Screws set 3/8 inch back from panel edges.
- Screw heads dimpled into the paper without breaking it.
Choosing a Screw Gun
A drywall driver has a depth-sensing nose that stops every screw at the same depth, removing the guesswork that causes torn paper and popped screws. Cordless drywall screwdrivers with brushless motors now match corded models on runtime and torque, and they take the extension cord off the job site.
The Drywall Installation Process and Cutting Openings
The full drywall construction and installation process runs from layout and cutting through hanging, taping, and priming. Each step has tolerances: panels are measured so seams land on framing, cut edges stay square, and fasteners land within the framing zone. Most manufacturers recommend hanging panels with the long edge perpendicular to the studs, so a 4-foot by 8-foot sheet spans three or four framing members and the horizontal seams land on solid backing.
From Panel to Painted Wall
- Measure the wall and cut panels, allowing a small gap at the floor.
- Fasten the panels with the screw pattern above, working from the center outward.
- Cut openings for electrical boxes and fixtures.
- Tape and finish the joints with three coats.
- Prime and paint.
Making Cutouts for Fixtures
Openings for switches, outlets, and light fixtures are the most error-prone part of hanging. Measuring each box location and transferring it to the panel beats eyeballing it. A cordless drywall cut-out saw spins a small bit at high speed and follows the pencil line without pulling the panel away from the framing, keeping the cut clean and the operator safe.
Drywall Safety: Dust Control and Protective Gear
Cutting and sanding drywall produces fine dust that irritates the lungs and the eyes. Gypsum dust is a mechanical irritant rather than a toxin, but joint compound can contain crystalline silica, which is linked to lung disease after years of heavy exposure. The exposure adds up over a career, and even one day of sanding without protection leaves a cough and irritated eyes that linger.
The Dust Risk
Exposure peaks during sanding, when compound dust hangs in the air long after work stops. Sanding releases particles small enough to reach deep into the lungs, and occupational guidance treats regular drywall work as a respiratory hazard, not a cosmetic annoyance.
Protective Measures
- Wear a dust mask rated for particulates, not a cloth face covering.
- Ventilate with open windows and a fan blowing outward.
- Use a HEPA vacuum to collect dust at the source.
- Seal doorways with plastic sheeting when working in occupied homes.
Finishing Tools That Cut Dust
Powered sanders change the exposure math. Cordless drywall sanders with vacuum attachments capture the dust at the pad instead of letting it drift, shortening cleanup and keeping more of the material out of the air in the first place.