Rust stains running down a balcony edge, cracks along a carpark ceiling, or a chunk of concrete on the ground that was not there yesterday. In Sydney, that usually means one thing: concrete cancer. The good news is that it can be fixed properly. The bad news is that it rarely fixes itself, and the longer it is left the bigger and more expensive the repair becomes.
What is concrete cancer?
Concrete cancer is the common name for spalling caused by corroding steel reinforcement. Reinforced concrete relies on the concrete around the steel to protect it. Over time, moisture and salt (especially in coastal areas) or carbonation of the concrete can break down that protection. Once the steel starts to rust it expands, sometimes to several times its original volume, and that expansion cracks the concrete from the inside and pushes pieces off the surface.
It is extremely common across Sydney, particularly in apartment buildings built from the 1960s to the 1990s, where the concrete cover to the steel is often thin and original waterproofing has reached the end of its life.
Warning signs to look for
- Rust stains bleeding from cracks or slab edges.
- Straight cracks that follow the line of the reinforcement, especially along balcony edges, beams and columns.
- Drummy concrete that sounds hollow when tapped, meaning it has delaminated from the steel.
- Spalling, where pieces of concrete have broken away.
- Exposed, rusted steel where cover has already been lost.
- Leaks from above, such as a failed balcony or podium membrane, which feed water to the steel.
Falling concrete is a safety issue. If pieces are dropping onto walkways, balconies or cars, the area should be made safe straight away and the repair prioritised.
Can concrete cancer be fixed?
Yes. Properly repaired concrete cancer can last for decades. The key word is properly. A repair that only fills the crack or patches the surface leaves rusting steel inside, and the problem returns. A proper repair follows a clear sequence:
- Locate every affected area by visual inspection and sounding, because the visible damage is often only part of it.
- Break out the damaged concrete to sound material and behind the corroded steel.
- Clean the steel back to bright metal, and add new bars where section loss is too great.
- Apply a corrosion inhibitor and primer to the reinforcement.
- Rebuild the section with an engineer-specified repair mortar, or formwork and recasting for larger areas.
- Protect the surface with an anti-carbonation coating or sealer, and fix the water source that caused it.
That last step matters. If a leaking balcony caused the concrete cancer, repairing the concrete without fixing the waterproofing only resets the clock.
What does concrete cancer repair cost in Sydney?
There is no honest single price, because the cost is driven by factors you cannot see until the concrete is opened up. The main ones are:
- Extent of damage: a single spalled patch versus corrosion along an entire balcony edge or carpark.
- Access: ground-level work versus scaffold, swing stage or elevated work platforms on a multi-storey building.
- Structural involvement: whether steel needs replacing and an engineer needs to design and inspect the repair.
- Associated work: re-waterproofing, re-tiling, balustrade removal and reinstatement, or coatings.
- Occupancy: staging work around residents, cars and businesses.
As a broad guide, a small, easily accessed repair is a modest job, a full balcony edge with re-waterproofing is a significant one, and whole-building programmes for strata schemes are major projects priced line by line. The only way to get a reliable number is an inspection and an itemised quote, which we provide free.
Why concrete cancer repairs fail
Most failed repairs have one of three causes: not enough damaged concrete was removed, the steel was not properly cleaned and treated, or the water source was never fixed. Each of those saves money on the day and costs far more a few years later.
Concrete cancer in strata buildings
In apartment buildings, concrete cancer on balconies, facades and carparks is usually common property and the owners corporation's responsibility to repair. For Class 2 buildings, remedial work is regulated under the Design and Building Practitioners Act 2020, so the builder should be registered. METCON holds DBP General Unrestricted registration (BUP4254812).
When to call a remedial builder
Call as soon as you see rust staining, cracking along the steel line or any loose concrete. Early repairs are smaller and cheaper. See our concrete cancer repair service, or send us photos of the damage and we will give you an initial view.
