What is Magnesite Flooring?

Magnesite flooring is a type of floor underlay that was widely used in Australian buildings, particularly from the 1920s through the 1980s. It became popular in Sydney and other urban centres, especially in unit blocks and strata buildings, where it was commonly installed beneath carpet or tile finishes.

Its use was driven by its affordability, ease of installation, and desirable properties for multi-residential and commercial settings.

Composition and Properties

Magnesite flooring is primarily composed of magnesium oxychloride cement, which is mixed with fillers such as sawdust, cork, and, in some cases, asbestos fibres.

The typical installation involves pouring a layer of magnesite, usually 15–25mm thick, directly onto concrete slabs to create a smooth, level surface.

Key benefits of magnesite flooring included:

• Soundproofing: Reduced noise transmission between floors.
• Fire resistance: Provided a degree of fire protection due to its mineral composition.
• Thermal insulation: Helped maintain comfortable indoor temperatures.
• Smooth finish: Created an even base for carpets or tiles.
• Sustainability (historically): Used recycled fillers like sawdust and cork.

However, the presence of hazardous materials such as asbestos in some magnesite mixes, and its high sensitivity to moisture, have led to significant concerns in modern building management[1].

Why Magnesite Flooring is No Longer Used

Magnesite flooring is no longer installed in new Australian buildings due to several critical issues:

• High moisture sensitivity: Magnesite absorbs moisture easily, leading to breakdown and damage over time.
• Chloride leaching: The magnesium chloride in magnesite can leach into the underlying concrete, causing corrosion of steel reinforcement (concrete cancer) and structural damage[2].
• Asbestos and silica dust hazards: Some magnesite floors contain asbestos, posing serious health risks if disturbed. Even without asbestos, removal can generate hazardous silica dust[3].
• Incompatibility with modern floor levelling and coverings: Modern adhesives and floor finishes are not compatible with magnesite, making repairs and overlays unreliable.

Risks and Issues Associated with Magnesite Flooring

Concrete Cancer and Spalling

When magnesite absorbs moisture, it releases chlorides that attack the steel reinforcement within the concrete slab. This process, known as concrete cancer, leads to rusting, expansion, and cracking of the concrete, often resulting in spalling (chunks of concrete breaking away)[2].

Health and Safety Risks

• Asbestos exposure: Some magnesite floors, especially those installed before the 1980s, may contain asbestos fibres. Disturbing these materials during removal or repair can release dangerous airborne fibres[3].
• Silica dust: Grinding or removing magnesite can generate fine silica dust, which is hazardous if inhaled[4].

Structural and Financial Risks

• Structural risks: Ongoing corrosion can compromise the integrity of the building, potentially leading to partial collapse or costly repairs.
• Property devaluation: Properties with magnesite flooring may be harder to sell or insure due to the associated risks.
• Common signs of magnesite damage:
  • Cracking or lifting of floor coverings
  • Damp or musty odours
  • Visible rust stains or concrete spalling
  • Uneven or soft spots in flooring

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Magnesite Floor Removal and Remediation

Why Removal is Recommended

Magnesite flooring is not considered repairable. Overlaying new flooring is not recommended, as underlying moisture and chloride issues will persist. Removal is the safest and most effective solution for long-term property health and compliance[5].

Typical Removal Process

1. Testing: Professional magnesite testing is conducted to check for asbestos and assess the extent of damage.
2. Safe removal: Licensed contractors remove the magnesite under strict safety protocols, especially if asbestos is present.
3. Concrete grinding: The concrete slab is ground to remove all magnesite residues and prepare for inspection.
4. Inspection and repairs: The slab is inspected for concrete cancer or spalling, and necessary repairs are carried out.
5. Floor levelling: Modern, compatible floor levelling compounds are applied to create a safe, smooth base for new flooring.

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Who Pays? Strata vs. Owner Responsibilities in NSW

In most NSW strata buildings, magnesite flooring is considered part of the common property. This means the owners corporation is typically responsible for testing, removal, and remediation.

However, individual owners may be responsible for replacing floor coverings after remediation. Always check your strata plan and seek professional advice[6].

Cost Factors

• Extent of magnesite coverage
• Presence of asbestos
• Level of concrete damage
• Waste disposal requirements
• Access and site conditions

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Magnesite Flooring - Frequently Asked Questions

Does magnesite always contain asbestos?

Not all magnesite floors contain asbestos, but many installed before the 1980s do. Testing is essential before any removal or disturbance[3].

Can you install new flooring over magnesite?

Installing new flooring over magnesite is not recommended. Moisture and chloride issues can damage new finishes and lead to further structural problems[5].

How long does removal take?

Removal time depends on the area, presence of asbestos, and extent of repairs needed. Most projects in residential units take several days to a week.

What are the legal/strata implications?

In NSW, the owners corporation is generally responsible for magnesite remediation as it affects common property. Owners should consult their strata manager and review their building’s by-laws for specific obligations[6].

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Sustainable and Safe Flooring Alternatives

Modern floor levelling compounds, such as cementitious or epoxy-based products, offer safe, durable, and sustainable alternatives to magnesite. CARAS is committed to sustainable remediation practices, including:

• Use of low-VOC, carbon-neutral materials
• Recycling and responsible disposal of hazardous waste
• Minimising environmental impact throughout the project lifecycle

As CARAS moves toward Climate Active carbon neutral certification, clients can be confident that building remediation projects are managed with a focus on both safety and sustainability[7].

Magnesite flooring presents significant risks to building safety, occupant health, and property value. Professional assessment, safe removal, and sustainable remediation are essential for protecting your investment and community.

CARAS offers expert guidance and end-to-end project management for magnesite floor removal, concrete cancer repairs, and sustainable building solutions.

Ready to see how we can help? Get in Touch

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References

[1] NSW Fair Trading. “Magnesite Floor Underlay.” https://www.fairtrading.nsw.gov.au/housing-and-property/strata-and-community-living/repairs-and-maintenance/magnesite-floor-underlay
[2] Engineers Australia. “Concrete Cancer: Causes, Prevention and Repair.” https://www.engineersaustralia.org.au/concrete-cancer
[3] Asbestos Safety and Eradication Agency. “Asbestos in Flooring.” https://www.asbestossafety.gov.au/about-asbestos/asbestos-materials/flooring
[4] Safe Work Australia. “Crystalline Silica and Silicosis.” https://www.safeworkaustralia.gov.au/silica
[5] Strata Community Association NSW. “Magnesite Flooring and Strata Responsibilities.” https://nsw.strata.community/magnesite-flooring
[6] NSW Government. “Strata Schemes: Repairs and Maintenance.” https://www.nsw.gov.au/housing-and-construction/strata/repairs-and-maintenance
[7] Climate Active. “Carbon Neutral Certification.” https://www.climateactive.org.au/what-carbon-neutral

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