Magnesite Flooring Removal in Strata Buildings

Magnesite is the defect nobody has heard of until it is theirs. It hides under the carpet of thousands of Australian apartments built from the 1960s to the early 1980s, and it usually announces itself during a renovation, a flooring change, or an investigation into damp, cracking or spongy floors. Then an entire owners corporation gets a fast education in slab chemistry. Here is that education, minus the panic, from an architect who designs remediation for class 2 buildings.

What magnesite is, and why it was used

Magnesite is a magnesium oxychloride cement, mixed with fillers like sawdust, laid as a topping over the concrete slab, typically 15 to 50 millimetres thick. Builders of the era loved it: it self-levelled rough slabs, softened footfall noise between units, and felt warmer underfoot than bare concrete. On its own terms it was a reasonable product. The problem is what it does when it gets wet.

Why it fails, and why that matters structurally

Magnesite is hygroscopic, meaning it absorbs and holds moisture, from a leaking balcony door, a bathroom, rising humidity, or a washing machine mishap. When it stays damp, the chlorides in the magnesium oxychloride migrate down into the concrete and attack the steel reinforcement. Rusting steel expands with real force, cracking and spalling the concrete around it, which is the mechanism people call concrete cancer.

That is the part committees need to absorb: wet magnesite is not a flooring problem, it is the start of a structural one. The topping itself also breaks down when damp, going soft, drummy or powdery, but the topping was never the point. The slab is the point. And because moisture is the trigger, magnesite trouble very often travels together with the waterproofing failures I deal with every week, which is why it belongs in this cluster alongside who pays for waterproofing defects.

One further caution: some magnesite mixes of that era contained asbestos. Test before disturbing it. This is a licensed-testing conversation, not a scrape-and-see one.

Who pays in NSW

Usually the owners corporation. The Registrar General's Common Property Memorandum lists the "sound proofing floor base (eg magnesite)" as an owners corporation responsibility, unless it was installed by an owner after the strata plan was registered. Strata law firms state the practical position the same way: magnesite is typically common property, so its removal and the slab repair beneath it fall under the strict section 106 repair duty.

The common wrinkle is renovations. When an owner strips magnesite to lay new flooring, the owners corporation will usually, through the renovation by-law, make reinstating the levelling and acoustic performance that magnesite was providing the owner's responsibility. If you are renovating an older apartment, find out whether magnesite is under your carpet before you approve the by-law and price the job, because discovering it mid-renovation reshuffles both the budget and the responsibility.

If your building was built before the mid 1980s and nobody has ever asked the magnesite question, it is worth asking deliberately rather than accidentally.

How removal should actually run

Ripping out magnesite is demolition. Doing it properly is remediation, and the difference shows up years later. The sequence I design:

1. Investigate first. Confirm it is magnesite, test for asbestos, map the moisture, and check the slab. Drummy concrete and exposed rusting steel change the scope entirely, and you want that known while the work is being priced, not discovered after the contractor mobilises.
2. Design the repair, not just the removal. The magnesite comes off, chloride-affected concrete is treated, corroded reinforcement is repaired, and then something must replace what magnesite was doing: floor levels (it was often the levelling layer, and 30 millimetres of missing height at every door and balcony threshold is a genuine design problem), acoustic separation between units, and waterproofing where wet areas or balconies adjoin. This is exactly the coordination work a designed remediation covers and a lone quote does not.
3. Tender it like for like. With a documented scope, several specialist contractors can price the same job. Without one, you are comparing guesses. The reasoning is the same as for any remedial work: a consultant's design versus a builder's quote.
4. Inspect the hold points. Slab repairs checked before they are covered, membranes tested before finishes, acoustic build-up verified. Then documented, so the building holds evidence of what was done under it.

On cost: sources publishing a reliable per-square-metre figure for magnesite removal do not really exist, and any number depends brutally on what the slab underneath looks like. Treat anyone quoting a tidy rate sight-unseen with suspicion. The honest sequence is investigation first, then a designed scope, then real prices.

If this is your building

Start with knowledge, not contractors. A Class 2 waterproofing consultation ($660, includes the diagnostic site visit) can establish what is under the floors, what the moisture is doing, and what the sensible scope looks like, and the full method is on the waterproofing remediation service page. Magnesite handled early is a manageable project. Magnesite ignored is a slab repair with a flooring problem on top.