Can Concrete Cancer Be Fixed? Yes — Here's How, and What It Costs in 2026

Concrete cancer is one of the few building defects that gets worse on a schedule you don't control. It also happens to be one of the most reliably fixable. If your building has rust stains bleeding down a soffit, hairline cracks running in straight lines along a slab edge, or lumps of concrete that sound hollow when tapped, the honest answer is: yes, this can be repaired, and repaired permanently — provided the repair addresses the corrosion mechanism rather than just the broken concrete.

Most of the money owners corporations waste on concrete cancer is spent on the second kind of repair.

What is concrete cancer, exactly?

Concrete cancer is the common name for corrosion of the steel reinforcement inside a concrete slab, beam, column or balcony. Steel rusting inside concrete expands to roughly seven times its original volume. That expansion has nowhere to go, so it cracks the concrete from the inside and pushes the surface layer off — the process engineers call spalling.

Two things usually start it. Carbonation: atmospheric CO₂ penetrates the concrete over decades and lowers its alkalinity until the passive layer protecting the steel breaks down. Chloride attack: salts, from coastal air or from chlorides in older concrete mixes, reach the bar and depassivate it locally. Sydney's coastal strip gives buildings both.

Can concrete cancer actually be fixed permanently?

Yes. Concrete cancer is permanently repairable when the corroded reinforcement is exposed, cleaned back to bright steel, treated, and reinstated in a repair mortar that is chemically compatible with the surrounding concrete. Repairs done to AS 1379 and AS 3600 principles, with the water source removed, routinely last 20 years or more. Repairs that only patch the surface fail within two to five years.

The reason the distinction matters so much is the incipient anode effect, sometimes called the halo effect. When you repair one patch with a new, highly alkaline mortar, the steel immediately outside that patch becomes electrochemically anodic — and starts corroding faster than it was before. That is why buildings that get "a few patches" done cheaply often come back within three years with a ring of new spalls around every old repair. Fixing concrete cancer properly means treating the zone, not the hole.

What does a proper concrete cancer repair involve?

A compliant repair follows six stages: survey and delineation, breakout, steel preparation, treatment, reinstatement, and protection. Each stage has a hold point. Skipping the survey or the protective coating is where most cheap repairs go wrong.

1. Survey and delineation. Hammer tap and, where warranted, half-cell potential or cover-meter testing to map every delaminated area — including sound-looking concrete with active corrosion underneath. The repair area is marked out beyond the visible damage.
2. Breakout. Concrete is removed to at least 20 mm behind the reinforcing bar, so the repair mortar fully encapsulates the steel. Square edges, no feathering.
3. Steel preparation. Bars are abrasive-blasted or needle-gunned to bright metal. Bars with more than about 15–20% section loss are supplemented or replaced under engineer direction.
4. Treatment. A zinc-rich or cementitious passivating primer is applied, or galvanic anodes are installed where the incipient anode risk is high.
5. Reinstatement. Polymer-modified repair mortar or, for larger volumes, formed-and-poured concrete, applied in specified lifts and cured properly.
6. Protection. An anti-carbonation coating over the repaired element, plus fixing whatever was letting water in — because the leak is the actual cause.

That last point is the one strata committees underrate. On balconies, concrete cancer is almost always a waterproofing failure wearing a structural costume. Repairing the concrete without renewing the membrane just resets the clock.

How much does concrete cancer repair cost in Sydney in 2026?

Indicative 2026 Sydney rates run roughly $900–$1,800 per square metre for localised patch repairs including access, and $2,500–$6,000 per balcony where waterproofing is renewed at the same time. Building-wide programmes on a mid-rise strata block typically land between $150,000 and $900,000. Access — scaffold versus rope access — is often 25–40% of the total.

These are indicative bands for budgeting a capital works fund, not a quote. The variables that move a number most are access method, whether the building stays occupied, the proportion of bars needing replacement, and how much of the damage is only found once breakout starts. Our detailed 2026 concrete cancer repair cost breakdown sets out how each line is built up.

What happens if concrete cancer is left untreated?

Untreated concrete cancer does not stabilise. Corrosion accelerates as cracking admits more water and oxygen, section loss in the reinforcement reduces the element's structural capacity, and spalling concrete becomes a falling-object hazard over entries and paths. Repair costs typically rise faster than inflation because scope grows non-linearly.

There is also a compliance dimension. Under the Design and Building Practitioners Act 2020, remedial work on Class 2 buildings must be designed and declared by registered practitioners. A committee that defers action after a written engineer's report is making a documented decision to defer — which matters if a defect claim, an insurance dispute or an owner injury follows later.

Who pays for concrete cancer repairs in a strata building?

In NSW, concrete cancer in slabs, beams, columns, balcony structure and the building's external fabric is common property under the Strata Schemes Management Act 2015, so the owners corporation pays — normally through the capital works fund or a special levy. Individual lot owners are rarely liable unless the damage stems from an unapproved lot alteration.

If the building is within the statutory warranty period, or the defect traces to original construction, recovery from the builder or developer may be available. That is a legal question, but the technical evidence — the defect survey, the photographic record, the repair scope — is what makes or breaks the claim, so get the investigation and reporting done properly before anyone starts breaking out concrete.

How do you tell concrete cancer from ordinary cracking?

Concrete cancer shows rust staining, cracks that follow the line of the reinforcement rather than wandering, hollow-sounding concrete, and drummy or lifting patches. Shrinkage cracks are random, fine, and free of rust. Structural movement cracks are diagonal or stepped and often widen at one end. Rust staining is the single strongest tell.

If you are unsure, a competent concrete damage diagnosis before any repair work will save more than it costs — because the repair strategy for carbonation, chloride attack and pure shrinkage cracking is entirely different, and scoping the wrong one is expensive.

How long does a concrete cancer repair take?

A small patch repair programme takes two to four weeks on site. A single balcony rebuilt with new membrane, screed and tiling takes two to three weeks, largely governed by membrane and screed cure times. Building-wide programmes run four to nine months, staged so residents lose access to any one balcony only once.

On a recent Chandos St, St Leonards programme, staging the concrete repairs alongside the waterproofing renewal meant each balcony was opened once rather than twice — which halved the resident disruption and removed a second mobilisation from the cost. That sequencing decision is usually worth more than any rate negotiation.

Getting it scoped properly

Concrete cancer is fixable. Whether it stays fixed depends on three decisions made before anyone lifts a hammer: was the full extent mapped, was the water source addressed, and was the incipient anode risk managed. Get those right and the repair outlasts most of the committee that approved it.

Atomic Projects is a Class 2 DBP Registered Building Practitioner and has delivered $20M+ of remedial work across 100+ Sydney strata buildings, from $50k balcony repairs to $5M+ facade programs. If you have an engineer's report, or just a soffit you don't like the look of, our concrete repair and remediation team can walk the building and tell you what you're actually dealing with.

Get a free assessment of your building's concrete condition.