Magnesium Oxide (MgO) Panels: Concerns and Risks

Magnesium oxide (MgO) panels have seen an increase in specification in recent years, particularly as an alternative to poured gypsum underlayment or concrete.

Promoted for their fire resistance and strength, these panels are increasingly used in commercial and multifamily construction. However, real world performance and independent testing have revealed significant concerns, particularly around moisture absorption, corrosion, and fire safety.

What are MgO Panels?

MgO panels are cementitious materials made from magnesium oxide (MgO). They are marketed as versatile, noncombustible building materials suitable for wall sheathing, subfloor, and structural applications.

Despite these claims, MgO panels, especially those manufactured overseas, have shown inconsistent performance due to inconsistent quality control, a lack of established testing standards, and limited long-term research.

Moisture Absorption, Weeping, and Corrosion Risks

One of the most critical issues with MgO panels is their hygroscopic nature, meaning that they readily absorb moisture from the air. This is true of any cementitious material, but MgO panels draw in more moisture than their counterparts. For example, when relative humidity (RH) increases from 50% to 80%, typical cement boards may double their water content, but MgO panels can quadruple their water content.

This excessive moisture can lead to a phenomenon known as “weeping,” where absorbed salts dissolve and migrate to the surface. This is more common in magnesium oxychloride (MOC) panels, which, due to poor quality control, may contain unreacted magnesium chloride (MgCl₂), also known as “free chlorides.” These chlorides aggressively absorb water vapor, forming a saline solution that corrodes fasteners, steel studs, and other metal components within an assembly.

Compounding this issue is the fact that MgO panels are installed by framers before the building is completely closed, increasing their exposure to moisture. The resulting corrosion of metal systems can only increase liabilities for both building owners and occupants.

Fire Performance and Noncombustibility Claims

MgO panels are often promoted as noncombustible alternatives to poured concrete, particularly in structural floor applications. However, recent third-party testing has shown that several leading MgO structural panels do not meet ASTM E136 standards for noncombustibility, contrary to manufacturer claims. 

Those associated with the manufacture and sale of MgO structural panels cite outdated or incomplete test reports to support their claims. In many cases, these reports:

• Refer to different panel thicknesses than those specified,
• lack sufficient detail to validate performance, or
• rely on tests that are not done in accordance with mandated testing protocols.

For deeper analysis, see this USG whitepaper, under The ”Support” Offered for Claims of Noncombustibility.

Supply Chain and Quality Control Challenges

Most MgO panels used in North America are imported from overseas manufacturers, which introduces several challenges, such as:

• inconsistent quality control due to a lack of standardized manufacturing practices,
• longer lead times and higher shipping costs, and
• material degradation¹ during extended storage and transit.

Without uniform oversight, even panels from the same supplier can vary in composition and performance—posing risks for both contractors and building owners.

Lack of Industry Standards and Research

The MgO panel industry is still emerging, and comprehensive, peer-reviewed research is limited, with most available studies focused on known issues like moisture absorption and corrosion. Additionally, there is currently no universally accepted standard for manufacturing or testing MgO panels, which makes it difficult for specifiers to verify performance claims.

This lack of transparency and consistency increases the risk of product failure and liability in critical applications like structural flooring or fire-rated assemblies.

Proceed with Caution

While MgO panels may offer some benefits in theory, their real-world performance raises serious concerns. Until more rigorous standards, testing, and quality control measures are in place, specifiers should carefully evaluate the risks and consider proven alternatives with established performance.

Sources

1. DuPont. Magnesium Oxide Panels: Emergence of a Modern Building Material.
   https://www.dupont.com/content/dam/dupont/amer/us/en/performance-building-solutions/public/documents/en/MgO-Panels-Emergence-of-a-Modern-Building-Material-White-Paper.pdf