What is Gypsum Wallboard

Drywall 101
First Published:
November 11, 2018
Last updated:
May 03, 2024

What is Gypsum Wallboard?

Gypsum wallboard is a general term that encompasses different types of large panels used for building walls, ceilings, and partitions. Gypsum wallboard is commonly used for interior wall construction but there are also special types of gypsum wallboard that can be used as exterior sheathing on buildings.

The most commonly used type of gypsum wallboard is drywall. DensGlass® made by Georgia Pacific is a common brand of gypsum wallboard panels used for exterior sheathing. Specialized Gypsum wallboard panels are also made for use as roofing boards, often in commercial building construction.

Gypsum is an ideal material for wall construction because of its fire-resistant properties and relatively inexpensive production cost. Gypsum-based plaster slurry can be formed into various-sized panels depending on the application.

Different materials can be added to plaster slurry to improve fire resistance, reduce weight, improve sound dampening, or achieve other goals. It provides an excellent base material for formed-in-place monolithic surfaces.

What is a monolithic surface?

According to Miriam Webster's dictionary, the term monolithic means "cast as a single piece" or "formed or composed of material without joints or seams". Gypsum panels are used in construction for creating monolithic surfaces. While it is true that drywall walls and ceilings have joints and are not "formed in place", once the joints are finished smooth and all the fasteners mudded over, the surface can be considered a monolithic surface.

The same is true about gypsum wallboard used in exterior sheathing. Inherently, there will be joints and seams when installing gypsum panels. However, once the surface is complete with a certain exterior finish application, the walls or ceilings are considered to be monolithic surfaces.

What is Gypsum?

Gypsum is a soft white rock known by mineralogists as hydrous calcium sulfate. The term hydrous indicates that it has some water in it. However, since the moisture is chemically combined with the other compounds in the rock, it is not readily present.

To make gypsum usable for construction, it is heated to temperatures over 350°F (176.6°C) and crushed into a fine powder. This powder can be mixed with water to make plaster of Paris. Plaster of Paris is a thick viscose material that can be poured into molds of all shapes and sizes.

Gypsum use in construction

Gypsum is the primary component of both drywall and plaster. After gypsum is turned into a dry powder, it is mixed with water and other materials and either poured into drywall panels or spread as plaster. Gypsum is used in other construction materials such as Portland cement, gypsum block, and exterior glass mat sheathing panels.

Gypsum is also used in quick set drywall mud. It is combined with other materials like clay, salts, plasticizers, and starchy glues. Ready-mix drywall mud usually is made with limestone and talc rather than gypsum though some types of ready-mix drywall mud may include gypsum

Mold Growth on Gypsum Wallboard Panels

Mold does not easily grow on the core of gypsum wallboard panels although it can grow on the material that covers the gypsum core. For example, mold growth can present a challenge with traditional drywall panels because the face paper used in drywall panels allows mold spores to feed and reproduce. However, since mold does not easily grow in the gypsum core, specialized types of drywall or gypsum wallboard can be produced that are better at resisting mold growth.

Mold-resistant drywall panels are usually made with face paper that has been treated with some chemical or additive that prevents mold growth. They can also be made with a different material that replaces the face paper with something better at preventing mold growth.

How to cut Gypsum Wallboard

Cutting gypsum wallboard is not difficult. Most gypsum wallboard panels can be cut with a straight edge and a utility knife. Because the gypsum core of gypsum wallboard panels breaks easily, cutting them generally consists of cutting the material on the outside of the panel and breaking the gypsum core along a straight line.

For example, to cut drywall panels, you simply score the drywall paper in a straight line and snap the board in half. Cutting DensGlass® panels requires a similar technique. DensGlass® panels are wrapped with a fiberglass material that provides strength to the panel and protects against inclement weather.

How to Install Gypsum Wallboard

Gypsum wallboard panels are usually installed with nails or screws. The type of screw fastener used depends on the backing material it is installed on top of. For drywall installed on wooden studs, nails or coarse thread screws can be used. Most commercial construction projects use metal studs. For metal backing, fine thread self-tapping screws are needed to install gypsum wallboard.

Gypsum Wallboard for Shaft Walls

Thick panels made of gypsum and face paper are used for building shaft walls. Shaft walls are not very common in residential construction but are usually seen in multi-level commercial construction projects.

Because shafts used for routing utilities in tall buildings span multiple floors, they have the potential to drastically increase the spread of fire. For this reason, shaft walls must be constructed in a way that provides superior fire protection.

Gypsum wallboard panels specially designed for shaft walls are usually very thick and have fiberglass added to increase their fire rating. Shaft wall panels can be installed using techniques similar to that of installing other gypsum wallboard panels such as drywall. However, the increased size and weight make installing shaft wall gypsum panels much more challenging than most.

In Summary

Gypsum wallboard panels are used in many areas of construction. Drywall is one very common example of gypsum wallboard used for building interior walls, ceilings, and partitions.