Magnesite flooring sits under the carpet in thousands of Sydney apartments, laid from roughly the 1920s through to the 1980s and most commonly in the post-war apartment boom of the 1950s to 1970s. Once it starts absorbing moisture, it attacks the concrete slab underneath it. MJ Engineering Projects assesses the condition of the slab, defines the scope of works and manages magnesite flooring repair and removal for owners corporations, strata managers and building owners across Greater Sydney.
We are remedial engineers, not floor installers. Our role is diagnosis, specification and delivery oversight, so the owners corporation ends up with a documented engineering position and a repair that holds.
Magnesite is a magnesium oxychloride cement, sometimes called Sorel cement. Magnesium oxide powder is gauged with a magnesium chloride solution and mixed with organic fillers such as sawdust, wood flour or cork, then trowelled over the structural slab as a levelling topping.
It set hard, took a smooth finish over rough concrete, felt warm underfoot and deadened sound between units. Before self-levelling compounds were common, magnesite flooring solved a real problem for builders. The problem is what happens when it gets wet.
Sydney’s post-war boom produced an enormous stock of red brick walk-ups and mid-rise blocks, and magnesite was a standard floor topping throughout. You find it through the inner city and the eastern suburbs, in blocks around Redfern and Surry Hills, in Darlinghurst conversions, in the walk-ups behind Maroubra and Eastgardens, and in older units scattered through Sutherland and Menai. If your building went up before the mid-1980s, magnesite flooring is worth ruling in or out rather than assuming.
Magnesium oxychloride cement is hygroscopic and partially water soluble. It draws in atmospheric moisture, and it draws in far more from a leaking shower, a failed balcony membrane, a burst pipe or a slab that has never been tanked.
As the material takes up water, chlorides migrate out of the topping and into the concrete slab. Chloride ions break down the passive oxide layer that protects reinforcing steel. Once that protection is gone, the reinforcement corrodes, and corrosion products occupy several times the volume of the original steel.
That expansion cracks the concrete from the inside. The result is Concrete spalling, commonly called concrete cancer: cracking, rust staining and eventually delamination of the slab soffit, which is the ceiling of the apartment, garage or lobby below.
Some magnesite mixes also used fillers that can contain asbestos, so any disturbance must be treated as a possible asbestos risk until testing says otherwise.
Any of these justify an inspection. Rust staining on a soffit means the reinforcement is already corroding and the issue is structural, not cosmetic.
Magnesite rarely affects one lot in isolation. It was laid floor by floor across whole buildings, so where one apartment has a problem, the topping in the units either side is usually the same age and the same condition.
That makes it an owners corporation issue, not a private one. In New South Wales, the owners corporation carries a strict duty to repair and maintain common property, and the structural slab is common property even though the floor covering above it generally is not. Where that boundary sits in your scheme, and what the by-laws say, is one of the first things a committee needs advice on.
Insurers and lenders also take a close interest in known structural defects. A cosmetic fix that leaves chloride-contaminated material in place can compromise a later claim, and it tends to reappear within a few years.
With over 18 years of industry expertise, MJ Engineering Projects provides tailored magnesite flooring repair solutions that safeguard structural integrity and extend the lifespan of buildings. Deteriorated magnesite can lead to concrete spalling, reinforcement corrosion and long-term safety risks if not addressed. Our consultants specialise in identifying these issues early and developing effective remedial strategies.
We combine advanced diagnostic tools with proven remedial techniques to deliver reliable outcomes. Each stage of the process, from inspection and specification through to tender management and project delivery, is carefully managed to ensure compliance with both the NCC and Australian Standards. Clients can rely on us for transparent reporting, quality assurance and durable repairs that protect property value and ensure long-term performance.
Once the inspection is complete, the engineer will develop a comprehensive repair plan that includes the scope of work, materials and methodologies required to ensure that all requirements are explicitly stipulated.
We produce a technical specification setting out methodology, materials and staging, written so contractors price the same thing and the committee can compare tenders fairly.
We run the tender for the owners corporation and assess submissions on scope and methodology, not headline figure alone.
We superintend the works, review quality at hold points and confirm the completed rectification against the specification.
Where contamination is established, the reliable answer is removal rather than overlay. Sealing or covering compromised magnesite leaves the chloride source sitting on the slab.
Removal work typically means containment and dust control, asbestos clearance where required, mechanical removal of the topping, grinding back the slab surface, then concrete repair to any spalled or delaminated areas before a new floor build-up goes down. Where corrosion is advanced, reinforcement may need to be exposed, cleaned or supplemented and the concrete reinstated.
Not every case needs full removal. Surface repair and moisture management can be appropriate where deterioration is limited, and the slab is sound. The investigation tells you which situation you are in.
Expect staging. Magnesite rectification happens inside occupied lots, so scheduling, access agreements and resident communication matter as much as the engineering.
Expect a funding conversation early. Committees usually need to consider the capital works fund, a special levy, or staging across financial years, and that decision is easier with a costed scope in front of them.
Expect documentation: an inspection report, a specification, a tender assessment and completion records. That paperwork is what defends the decision later, whether the question comes from an owner, an insurer or a tribunal.
MJ Engineering Projects has more than 18 years in remedial engineering and has inspected and rectified defects on more than a thousand Sydney buildings. We are a NSW Fair Trading Registered Design Practitioner, listed on the National Engineering Register, members of Engineers Australia and the Strata Community Association NSW, and certified to ISO 9001, ISO 14001 and ISO 45001.
If you suspect magnesite flooring in your building, contact us for an inspection and a written opinion.
Here are some key results we’ve delivered for Magnesite Flooring Repair.
With more than eighteen years of proven experience in remedial engineering, our firm has built a strong reputation for delivering reliable and long-lasting results. As registered design practitioners, we specialise in repairing building defects across a wide range of projects, from heritage façades that require delicate restoration to modern high-rise towers that demand technical precision.
Our structured project management approach, combined with thorough quality control processes, ensures every repair is handled with efficiency and care. We focus on minimising disruption, controlling costs and tailoring repair strategies to meet the unique requirements of each client.
This commitment to detail and excellence enables us to consistently provide durable, value-driven solutions that stand the test of time.
Our engineers bring extensive expertise in remedial engineering, supported by years of specialised experience and a detailed understanding of industry standards. We take pride in delivering tailored remediation strategies that address both visible and hidden defects across a wide range of building types.
By staying informed of changing regulations and compliance requirements, our team ensures every project achieves technical excellence and long-term durability. We also place a strong emphasis on sustainability, applying environmentally responsible practices and innovative methods wherever possible.
From diagnosing complex issues to implementing cost-effective repair programs, we are committed to providing clients with outcomes that are reliable, compliant and built for the future.
We have successfully completed inspections and remedial work on more than one thousand residential, commercial and industrial buildings across Sydney. This extensive experience allows us to identify and resolve issues with accuracy, from water ingress and façade deterioration to concrete spalling and structural concerns.
Each project benefits from a customised repair strategy designed to achieve durability, compliance and lasting performance. Our large and diverse portfolio equips us to anticipate challenges, optimise resources and streamline delivery to minimise site disruption.
With this proven track record, we are confident in managing projects of any scale or complexity, delivering solutions that are efficient, cost-effective and built to endure.
Our credentials reflect a strong commitment to professional standards, compliance, and continuous improvement. We maintain active involvement with leading industry bodies and hold recognized certifications and registrations, including ISO Certifications and NSW regulatory registrations.
View our capability statement for a full overview of our services, credentials and project experience.
Don’t let magnesite deterioration compromise the safety and value of your property. Take proactive steps today by choosing MJ Engineering for comprehensive magnesite repair solutions provided by our industry-leading specialists in Australia.
With over 18 years of industry-leading experience and a track record of inspecting and protecting over 1,000 buildings in Sydney, we offer unmatched expertise and reliable solutions tailored to your specific needs. If you have any questions, contact our team, who will be happy to assist.
Key Concerns and Frequently Asked Questions About Magnesite Flooring Repairs
Everything you need to know about MJ Engineering Projects. Can’t find the answer you’re looking for?
Chat With Our Team Now.
Magnesite is a magnesium oxychloride cement topping laid over concrete slabs in Australian buildings from roughly the 1920s through to the 1980s, and most commonly in the post-war apartment boom of the 1950s to 1970s. It absorbs moisture, and as it does, chlorides migrate into the slab and corrode the reinforcing steel. That corrosion expands and cracks the concrete, producing spalling in the ceiling of the space below.
Magnesite is usually hidden under carpet or vinyl, so it is often found during a renovation. Signs include a soft or spongy floor, a musty smell, brown staining bleeding through floor coverings, and rust staining or cracking on the ceiling of the unit below. An inspection by a remedial engineer confirms it.
Sometimes. Where deterioration is limited, and the slab is sound, surface repair and moisture management can be appropriate. Where chloride contamination has reached the reinforcement, removal of the topping and repair of the concrete is generally the durable option. Diagnostic investigation is what determines which applies.
In New South Wales, the structural slab is common property, and the owners corporation has a duty to maintain it, while floor coverings within a lot are usually the owner’s responsibility. The exact split depends on the strata plan and the scheme’s by-laws, so committees should get advice before committing to a cost apportionment.
Some magnesite mixes used fillers that can contain asbestos, so it cannot be ruled out by appearance alone. Any building with magnesite should have the material tested before it is disturbed, and licensed removal arranged if asbestos is confirmed.
We collect your information to assess your enquiry, prepare your proposal, and manage our client relationships in accordance with our Privacy Policy.
