The Great Wall of China and the Roman Empire represent the first uses of magnesia mixed into mortar. By the 20th-century, the use of magnesia declined as builders turned to cheaper options such as Portland cement and other such materials.
Over the past two decades, magnesia has returned as a component found in sustainably produced magnesium oxide boards. Several states encourage and approve builders using magnesium boards to combine strength and versatility with sustainability and recyclability.
Magnesium oxide boards offer replacements for gypsum-based panels, drywall, and other construction boards and panels. They are environmentally benign and boast a host of characteristics beneficial to the safety and health of homeowners and contractors.
Still, many consumers haven't heard of magnesium board or understand its outstanding features and environmental attributes. It’s a bit of a mystery, and only a few websites have much information about magnesium oxide boards.
With that in mind, let’s look at several commonly asked questions about magnesium oxide boards.
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By Frank Jossi, Rise Writer
Mar 28, 2025 · 5 min read
No, they are moisture-resistant, not waterproof. Extended water exposure leads to hydrothermal expansion. Shorter periods cause no swelling or warping. Magnesium board sellers say exposure of more than an hour may be harmful. Still, magnesium board underneath basement flooring boards protects against moisture. In coastal areas, magnesium board generally withstands salt damage. Outside, the boards should always be covered with another layer of materials or coated.
Yes, and magnesium board advocates often cite their fire resistance. It’s highly resistant to flames and carries a UL 055 rating and an A+ from the ATSM. The boards do not spread flames or smoke.
Many environmental benefits come with magnesium board. The curing process captures carbon dioxide. Unlike other competitive materials, the board contains no asbestos, formaldehyde, ammonia, silica, or benzene. The chloride content generally falls below eight percent.
The manufacturing of magnesium board uses 25 to 50 percent of the energy required to prepare calcium hydroxide (slaked lime) or Portland cement. When it comes to downsides, most raw materials used to make magnesium boards come from China and travel long distances. This negatively affects its total embodied energy and increases its carbon footprint significantly.
Manufacturers generally use no volatile organic compounds or toxic ingredients in producing the boards. Contractors and homeowners should wear proper silica/concrete dust respirators when cutting and sanding the boards before installation.
The boards are considered nutritional waste that can be recycled, recycled, or ground up and mixed into soil for nourishment. They create no pollution in landfills.
The first is cost. Magnesium boards cost more than gypsum boards but come close to cement board prices. The quality varies significantly among board manufacturers, with experts suggesting cheaper board provides lower quality performance, not surprisingly. Boards can have unique installation needs, demanding contractors, and do-it-yourselfers follow directions. Some boards may not work as well in humid climates.
Homeowners need to take precautions to avoid small cracking. Cracking can occur if the steel or wood framing behind the panels shrinks. Wind and earthquakes will cause cracks. However, those issues remain relatively minor. Most panels installed indoors suffer no damage because the ambient temperature does not change significantly. To avoid cracking, experts suggest allowing for a small gap between boards. A non-shrink caulk should fill space. Paint a primer as a first coat and moisture-absorbing paint.
Companies selling the boards cite several reasons why the additional cost of gypsum boards makes them worth it. Hanging panels using a tile approach makes installation quicker than other boards. They don’t need corner beads, a necessity with gypsum. The panels need no backing materials for cabinets, shelving, and other hanging installations. Since the boards slightly expand, less bracing may be required.
Contractors and DIYers should store boards in a cool, dry area in flat stacks placed on the material instead of the ground. Put nothing on top of the boards to avoid bowing. Place the boards in rooms where they will be installed for two days, prior to installation, to allow them to acclimate.
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Any standard finish works on the board, including concrete and synthetic stucco, paint, plaster, stone, tile, brick, fabric, and wallpaper. The panels need a concrete or masonry primer, followed by paints and topcoats. Ask at your paint store for brands and product types that bond well with magnesium oxide boards – several adhere particularly well. Experts suggest testing the paint’s adhesiveness before a full application.
Yes, their adhesive characteristics make for excellent Structural Insulated Panels (SIPS) and Exterior Insulated Finish Systems (EIFS). These systems improve a wall's fire rating, insulation, and moisture resistance. Many companies are beginning to sell MgO boards as part of structural wall systems, rather than individual panels.
Rise Writer
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Based in St. Paul, Frank Jossi is a journalist, editor and content strategist. He covers clean energy in Minnesota for Midwest Energy News and writes frequently for Finance & Commerce. His work has appeared in more than 70 local, national and international publications.
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Most magnesium carbonite comes from China and Europe. The process combines magnesium and oxygen with pressure and heat to create magnesium oxide (MgO). The MgO has the characteristics of stone after heating. After being ground into powder, it gets mixed with water, chloride, and sulfate (or Epsom salts) and wood dust (cellulose), perlite, and a handful of other materials.
The board works in almost every situation in a home. Magnesium board products can be applied as wall sheathing, trim, fascia, and siding on the exterior. Inside homes, magnesium board serves as a tile backer, wall panel, ceiling board, firewall, and drop ceiling tile. Dryboard can also incorporate magnesium boards.
Yes, magnesium oxide boards work the same way as drywall or oriented strand board, or any other board product. Builders need no special tools to cut, nail, score, snap, screw, or hang magnesium boards from wood or steel frames. Boards come in thicknesses from 3 to 20 millimeters, with surfaces offered including rough texture, smooth face, versatile, and utility styles. Contractors can finish the boards with paint (just two coats), concrete, and wallpaper.
Magnesium oxide board has many attractive qualities. As highlighted earlier, it has excellent fireproof qualities, is energy efficient to produce, reduces waste, and captures carbon dioxide during production. Beyond that, the boards’ fungus resistance means they attract no rot, mildew, allergens, or mold. It’s 20 to 30 percent lighter than other cement-based boards. Contractors and DIYers find it easy to use because of its lightweight.
Not a great deal. But a group of scientists looked at the issues with magnesium boards, some which emerged in commercial buildings.
