Why Your “Renovated” Apartment Floor Might Still Have Magnesite Underneath

Magnesite flooring is a magnesium oxychloride cement compound widely used as a levelling screed in Australian apartment buildings constructed between the 1950s and 1980s. In many Sydney strata properties , previous owners or contractors installed new flooring directly over magnesite without removing it. This concealed layer can cause moisture damage, structural cracking, and costly remediation failures when the property is renovated again.

You bought an apartment with fresh carpet. Or perhaps a floating floor, new vinyl planks, or engineered timber. It looked finished. It felt solid. The real estate listing called it “recently renovated.” So when you decided to upgrade again, you expected to pull back a layer and find clean concrete underneath.

Instead, you found a brittle, discoloured, chalky layer that crumbled under the scraper. That layer is magnesite , and across Sydney’s older apartment stock, its presence under “new” flooring is far more common than most owners expect.

This is not a cosmetic issue. It is a building condition problem with implications for compliance, structural integrity, and the cost of any future renovation work. For owners in NSW strata buildings, understanding what sits beneath the visible floor surface is essential before committing to any flooring project.

What Is Magnesite Flooring and Why Does It Remain Hidden Under Renovated Surfaces? Magnesite, formally known as magnesium oxychloride cement , was a standard floor levelling and finishing material in Australian residential construction from the post-war period through to the early 1980s. Builders applied it as a screed over concrete slabs to create a smooth, level surface for carpet, tiles, or vinyl. In many apartment buildings across Sydney’s inner suburbs, the Eastern Suburbs, and the lower North Shore, magnesite was the default substrate beneath finished floors.

The material served its purpose well at the time. It levelled uneven concrete, provided a smooth finish, and was cost-effective at scale. The problem emerged decades later, when building science caught up with the material’s limitations:

Moisture sensitivity: Magnesite absorbs and reacts to moisture, causing it to expand, crack, and break down over time. Chloride migration: Magnesite contains chloride compounds that can corrode the steel reinforcement within a concrete slab, particularly in the presence of moisture. Adhesion failure: New flooring adhesives and underlayments often do not bond reliably to magnesite surfaces, leading to delamination. When a previous owner or contractor decided to install new flooring, the typical approach was simple: lay it over the top. Removing magnesite was seen as an unnecessary expense, especially when the surface appeared level and intact. Carpet could be laid over it with minimal preparation. Floating floors could sit on underlay without direct adhesion. Vinyl planks could be glued down if the surface was reasonably smooth.

The result, across thousands of Sydney apartments, is a layered flooring system where the visible surface is relatively modern, but the substrate beneath it is original, ageing, and potentially compromised.

How Does This Impact Sydney Apartment Owners During Renovation? The discovery typically happens at the worst possible time: mid-renovation. The owner has committed to new flooring. Materials have been ordered. Trades are booked. Then the existing floor covering is removed, and the magnesite layer is exposed for what may be the first time in decades.

At this point, the owner faces several immediate problems:

The new flooring cannot be installed as planned. Most modern flooring products require a stable, dry, compatible substrate. Magnesite does not reliably meet these requirements, particularly for adhesive-fixed products such as vinyl plank, hybrid flooring, or engineered timber glued to slab. The renovation timeline extends significantly. What was planned as a two- or three-day flooring swap becomes a multi-stage remediation project involving removal, disposal, concrete assessment, grinding, levelling, and then installation. Costs escalate beyond the original budget. The scope of work has fundamentally changed, and the additional labour, materials, and disposal requirements are not trivial. Strata approval may be required. In NSW, the concrete slab beneath the magnesite is typically common property. Removing magnesite that has damaged the slab, or grinding into the slab surface, may require strata committee or owners corporation approval under the Strata Schemes Management Act 2015 . The assumption that “new flooring means a new substrate” is one of the most costly misconceptions in Sydney apartment renovation. The floor you see is rarely the floor that matters. For owners who have already invested in a renovation that unknowingly installed flooring over magnesite, the problem compounds over time. Moisture from cleaning, spills, humidity, or rising damp continues to affect the magnesite layer. The flooring above may begin to lift, bubble, crack, or develop odours. When that flooring is eventually removed, the condition of the underlying magnesite is often significantly worse than it was at the time of the original overlay.

Why Is Magnesite Removal Important for NSW Compliance and Building Safety? Magnesite removal is not simply a renovation preference. In many cases, it is a necessary step to address building defects that carry compliance and safety implications.

Under NSW building and workplace safety frameworks, several regulatory considerations apply:

Asbestos risk assessment: In some older installations, magnesite may be bonded with or sit adjacent to asbestos-containing materials . SafeWork NSW: Asbestos Safety and Management requires appropriate identification and management of asbestos before any demolition or removal work proceeds. A competent person must assess the material before disturbance. Concrete slab integrity: Prolonged exposure to chloride-rich magnesite can cause concrete cancer , where embedded steel reinforcement corrodes and expands, cracking the slab from within. This is a structural issue that falls within the responsibility of the owners corporation for common property slabs, as outlined by NSW strata guidance . Moisture and waterproofing: Ground-floor and basement-level apartments are particularly vulnerable. If magnesite has absorbed moisture from the slab below, conditions for mould growth and ongoing substrate degradation are present. NSW Fair Trading: Strata Living and Maintenance Obligations provides guidance on building maintenance obligations that may apply. Disposal requirements: Magnesite waste, particularly if contaminated, must be disposed of in accordance with NSW Environment Protection Authority guidelines. It cannot be treated as general construction waste in all cases. Ignoring these considerations does not make them disappear. It simply transfers the cost and risk to a future owner or to the owners corporation when the slab requires major remediation. The Strata Community Association NSW has increasingly highlighted ageing building substrate issues as a governance priority for strata committees across the state.

What Does Magnesite Removal Typically Cost in Sydney? Costs vary based on the area affected, the condition of the magnesite, the depth of contamination into the concrete slab, and the type of new flooring intended for installation. The following provides a general guide for Sydney apartment projects as of 2025.

Magnesite Inspection and Testing Estimated cost range: $350 to $700 Notes: Includes material sampling, moisture reading, and substrate assessment. Magnesite Removal Estimated cost range: $55 to $130 per square metre Notes: Depends on thickness, adhesion to the slab, and access conditions. Concrete Grinding Estimated cost range: $30 to $75 per square metre Notes: Required to prepare the slab after magnesite removal. Concrete Repair and Levelling Estimated cost range: $25 to $65 per square metre Notes: May be required where slab damage from chloride exposure is present. Waste Removal and Disposal Estimated cost range: $600 to $2,500 Notes: Volume-dependent; contaminated material increases cost. New Flooring Installation Estimated cost range: $45 to $150+ per square metre Notes: Varies by product, including hybrid, engineered timber, vinyl, or carpet. For a typical two-bedroom Sydney apartment with 60 to 80 square metres of flooring, a full magnesite removal, slab preparation, and new flooring installation project generally ranges from $8,000 to $22,000 , depending on the factors above. Properties with significant slab damage or asbestos-related requirements will be at the higher end of this range or above it.

These figures should be considered against the alternative: installing new flooring over compromised magnesite and accepting the likelihood that the project will need to be repeated within five to ten years, at greater expense.

What Are the Risks of Leaving Magnesite Under a New Floor? Owners who discover magnesite during renovation and choose to install over it rather than remove it are accepting a defined set of risks:

Adhesion failure: Flooring products that require glue-down installation, including vinyl plank, hybrid flooring with adhesive, and engineered timber, are at elevated risk of delamination when installed over magnesite. The substrate does not provide a reliable bonding surface, and moisture migration from within the magnesite can break down adhesives over time. Moisture trapping: Placing a new impermeable floor covering over magnesite creates a sealed environment where moisture cannot escape. This accelerates the degradation of the magnesite and can lead to mould growth, odour, and eventual failure of the flooring above. Ongoing slab corrosion: If the magnesite contains chloride compounds and the slab beneath has embedded steel reinforcement, the corrosive process continues regardless of what is placed above it. Concealing the problem does not stop it. Reduced property value: Pre-purchase building inspections in Sydney increasingly include substrate assessments. A report that identifies undisclosed magnesite, or evidence of a flooring overlay concealing an unresolved substrate condition, can affect sale negotiations and buyer confidence. Warranty exclusion: Most flooring manufacturers specify acceptable substrate conditions for their product warranties. Installing over magnesite, particularly without disclosing it, may void manufacturer warranties on the flooring product itself. The financial logic of avoiding removal is understandable in the short term. But the arithmetic shifts when the full lifecycle cost is considered: a floor installed twice over ten years costs more than a floor installed once over twenty years on a properly prepared substrate.

What Is the Correct Process for Removing Magnesite in a Sydney Apartment? Proper magnesite removal is a multi-stage process that requires the right equipment, experienced operators, and an understanding of what lies beneath the magnesite itself. The typical sequence is as follows:

Initial inspection and testing: A qualified technician assesses the flooring, takes moisture readings, identifies the magnesite layer, and determines whether asbestos testing is required based on the building’s age and construction history. Asbestos clearance, if applicable: If asbestos is identified or cannot be ruled out, a licensed asbestos assessor must be engaged. Work cannot proceed until clearance is provided under SafeWork NSW requirements. Floor covering removal: The existing carpet, vinyl, floating floor, or other surface material is removed to expose the full magnesite layer. Magnesite extraction: Using mechanical scrapers, grinding equipment, and, in some cases, pneumatic tools, the magnesite is removed from the concrete slab surface. This is labour-intensive work that requires care to avoid unnecessary damage to the slab. Concrete assessment: Once the magnesite is removed, the slab surface is inspected for chloride contamination, cracking, spalling, and reinforcement exposure. Concrete grinding is typically required to remove residual magnesite and prepare a clean, profiled surface. Slab repair and levelling: Damaged areas are repaired. The slab is then levelled using a compatible compound to create a uniform, specification-compliant surface for the new flooring. Professional floor levelling ensures the new substrate meets manufacturer requirements for flatness and moisture content. Moisture testing and certification: Before new flooring is installed, the prepared slab must pass moisture testing to confirm it is within acceptable limits for the chosen flooring product. New flooring installation: With the substrate fully prepared, the selected flooring is installed to manufacturer specifications, with appropriate underlayment, adhesive, or fixing method. Each step in this process exists for a reason. Skipping any stage, particularly concrete assessment and moisture testing, introduces risk that the same pattern of failure will repeat.

Why Choose Elyment Property Services for Magnesite and Floor Remediation in NSW? Elyment Property Services operates across the full scope of apartment floor remediation in Sydney. This is not a single-trade service. It requires integrated capability across inspection, removal, disposal, concrete preparation, levelling, and flooring installation, all coordinated within a single project workflow.

Elyment’s approach to magnesite remediation in Sydney apartments includes:

End-to-end project management: From initial substrate assessment through to final flooring installation, the entire process is managed by one team. There is no handoff between separate contractors, no gaps in communication, and no ambiguity about scope responsibility. On-site capability: Elyment operates its own warehouse, showroom, and logistics infrastructure in Sydney. Equipment, materials, and trades are coordinated from a central operation rather than assembled ad hoc for each project. Compliance-aware execution: Every project is assessed against NSW regulatory requirements, including SafeWork asbestos protocols, strata approval processes, and waste disposal regulations. Documentation is maintained throughout. Material supply and installation: Elyment supplies and installs a full range of flooring products suited to post-magnesite remediation projects, including options specifically selected for compatibility with prepared concrete substrates. Transparent quoting: Project costs are broken down by stage: inspection, removal, grinding, levelling, disposal, and installation. There are no hidden line items and no scope ambiguity. Sydney apartment owners facing a magnesite discovery mid-renovation need a service provider that understands the full chain of dependencies: what must happen first, what depends on what, and where the cost and compliance risks concentrate. That is the operational model Elyment is built to deliver.

Discovered Magnesite Beneath Your Floor? Get a substrate assessment before you renovate.

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Sources and References SafeWork NSW: Asbestos Safety and Management NSW Fair Trading: Strata Living and Maintenance Obligations Strata Schemes Management Act 2015 (NSW) NSW Environment Protection Authority Strata Community Association NSW Australian Journal of Construction Materials: Magnesite Degradation in Concrete Slabs