Published | 07-24-2020

Quality in the Crystals

Unless you’re a real nerd for geology, chances are you’ve probably never heard of gypsum. But you can be sure you’ve seen it everywhere. A soft mineral made of calcium sulfate dihydrate, gypsum’s pliable yet durable properties make it an ideal ingredient in a wide variety of products used often in the modern world—which works out well since it’s the most commonly found sulfate mineral and often easily mined.

Gypsum is commonly used in many industries for everything from soil and fertilizer to cement and drywall to ornamental alabaster and dental plaster. The casts traditionally used to reset broken bones? They’re made from plaster of Paris, a derivative of gypsum. Like we said, gypsum’s everywhere.

But specifically in construction, when used in building materials, gypsum provides many benefits you may not be aware of when approving materials to use on your next project. Here’s a quick overview.

Gypsum in Construction

Gypsum’s use in building construction dates back to ancient times, when early Mediterranean civilizations used it for mortar. Gypsum plaster of Paris is the literal building block of the Egyptian pyramids. And the word gypsum itself derives from ancient Greek gypsos. Early Roman empire engineering saw the development of the first concrete for advanced aqueducts and the mind-bending Pantheon dome structure. And by the time of the Italian Renaissance, artists and architects were experimenting with modeling stucco and adding paint to wet drywall to create elaborate frescos.

As technology advances and our understanding of the natural world expands, so does our understanding of this crucial mineral’s benefits in building our societies. A surprisingly helpful benefit that today’s construction industry sees in gypsum-based materials is its resistance to fire—which means using gypsum products in strategic structural locations can help to mitigate a building’s risk of fire damage.

Pure gypsum (known as calcium sulfate dihydrate) occurs naturally in crystal form, including two molecules of crystalized water. Synthetically made gypsum has these same properties. This means that 21% of gypsum is naturally made up of water that is chemically combined with calcium sulfate. In the event of a fire, this water gradually releases as vapor, while oxidizing the remaining calcium sulfate, which remains inert up to temperatures as hot as 2,200o Fahrenheit. For building materials made with gypsum, this slowing of the calcination process can also help to slow the burning of organic materials in a fire.

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Roofing’s Superior Material

In the right material compound, gypsum also adds incredible strength. When used in roof boards, gypsum has been shown to increase the board’s compressive strength by hundreds of pounds per square inch. For instance, a common roof board material high-density polyiso (HD ISO) is made from rigid foam and capable of holding about 80-140 psi, whereas gypsum roof boards have been shown to hold up to 900 psi. That extra strength makes a big difference when supporting heavy equipment like HVACs and solar paneling.

Because of gypsum’s inert properties and internal water crystals, including a gypsum-based roof board in the thermal barrier or cover board position adds a layer of strong, fire-resistant support against the damaging effects of equipment, foot traffic, fire, wind, and more. In the cover board position, a gypsum roof board helps protect the building from external sources of ignition—such as wildfires or other buildings’ flames. This mitigates the risk of an external fire spreading to your building from embers or other ignition sources landing on the roof. And in the thermal position (beneath the insulation), a gypsum roof board helps slow the spread of internal structure fire throughout the rest of the building by cutting off the supply to additional organic roofing materials to fuel the flames.

DensDeck® Prime Roof Boards offer superior fire resistance are made from durable gypsum with a strong fiberglass mat that helps maintain a solid foundation and lessen repair needs before the roof’s time. To learn more about how gypsum enhances DensDeck Prime’s performance capabilities to protect your building’s roof and the assets stored within, visit

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Want to learn more about cover boards? Have a new roof construction project? Need assistance on a roof remodel?


Want to learn more about cover boards? Have a new roof construction project? Need assistance on a roof remodel?