Magnesium Oxide Board
Summary
Magnesium oxide board is a panel of magnesia cement, most often Sorel cement (magnesium oxychloride), with fiberglass facing and no paper. It resists fire, mold, and impact, but its chlorides can corrode fasteners and steel studs, and Sorel-based boards can attract moisture.
Cols
Terminology
- MgO / magnesia: magnesium oxide
- Sorel cement: magnesium oxychloride cement, the most common binder
- Periclase: magnesium oxide mineral source
History and demand
First uses in construction
- Magnesia cement used in ancient masonry, including the Great Wall of China
- Portland cement replaced magnesia for masonry in the 20th century
- Around 2003: magnesia cement boards approved for US construction
Sourcing
- China produced about 68 percent of world magnesia in 2023, about 16 million tonnes, and held about 70 percent of capacity, mostly in Liaoning Province (Euromines)
Composition and production
Raw materials
- Magnesium oxide in magnesia cement; fiberglass backing, no paper facing
- Major periclase deposits in China, Europe, and Canada; US deposits negligible; China restricts export of raw materials
Manufacturing process
- Magnesite calcines at about 780°C (1,436°F), versus over 1,400°C (2,552°F) for portland cement
Properties
Fire behavior
- Tested to UL and ASTM fire methods with an A rating
Durability
- Non-nutritive to mold, fungus, and insects (ASTM G21)
- Tested through 36 months of freeze-thaw cycling
- Impact resistance tested to ASTM D5628; Miami-Dade County hurricane and impact approval
- STC 53 to 54
Uses in buildings
Building elements
- Fire-Rated Assemblies: fire-resistive boards
- Acoustics: sound-control wall assemblies
Pros and cons
Pros
- Fire, mold, and insect resistance
- Free of silica and asbestos
- Cost comparable to portland cement backer board
Cons
- Chloride can corrode embedded fasteners and steel studs
- Sorel-based boards are slightly hygroscopic and can "cry" in humid climates
- Costs more than paper-faced gypsum drywall
Manufacturing and cost
Main manufacturers and suppliers
Sources
- Wikipedia: Magnesium oxide wallboard, https://en.wikipedia.org/wiki/Magnesium_oxide_wallboard
- Wikimedia Commons: MgO wallboard 10mm.jpg, photo by Findoutwhy (CC BY-SA 3.0), https://commons.wikimedia.org/wiki/File:MgO_wallboard_10mm.jpg
- Euromines and RHI Magnesita: magnesia market study, January 2025, https://www.rhimagnesita.com/wp-content/uploads/2025/02/euromines-magnesia-market-study-january-2025.pdf