Concrete cancer is one of the most common defects on Sydney apartment and commercial buildings, especially near the coast. Left alone it gets worse every year, and at height it becomes a safety risk when pieces of concrete start to fall. Caught early, it is usually a contained, manageable repair.
This guide explains what concrete cancer is, how to spot it, why it happens and how it is repaired by rope access without scaffolding the whole building.
What is concrete cancer?
“Concrete cancer” is the common name for spalling caused by corroding steel reinforcement. When water and chlorides reach the reinforcing bar inside the concrete, the steel rusts. Rust takes up more space than steel, so it pushes the concrete cover off from the inside. The result is cracking, rust staining and eventually pieces of concrete breaking away.
Early warning signs
- Cracks running along balcony edges, slab edges, columns or window heads
- Rust stains bleeding through paint or render
- Bulging, bubbling or flaking paint over concrete
- A hollow or “drummy” sound when the surface is tapped
- Pieces of concrete on balconies or the ground below
- Exposed, rusted reinforcement
The areas we find it most often are balcony slab edges, parapets, window heads and sills, columns and anywhere water sits or drains poorly.
Why it happens on Sydney buildings
- Water getting in. Cracks, failed sealant, poor drainage and damaged membranes let water reach the steel.
- Salt air. Chlorides from the coast accelerate corrosion, which is why coastal suburbs see more of it. See our article on coastal building maintenance.
- Low concrete cover. On older buildings the steel is often too close to the surface.
- Age and carbonation. Over decades the concrete’s natural protection of the steel reduces.
Why it should not be left
Concrete cancer does not stop on its own. As corrosion continues, the repair area grows and so does the cost. On a multi-storey building the bigger concern is safety: loose concrete falling from a balcony edge onto a footpath, courtyard or car park. Owners corporations also have obligations to maintain common property, so a documented plan to deal with it matters.
How we inspect it by rope access
- Visual survey. Technicians descend each affected drop and look closely at cracks, staining and spalling.
- Sounding. Surfaces are tapped to find hollow, delaminated areas that are not yet visible.
- Make safe. Any loose concrete that could fall is removed during the inspection.
- Mapping and report. Each defect is photographed and located, so the scope and cost can be agreed before repairs start.
Where damage is extensive or structural, we recommend involving a structural or remedial engineer to specify the repair.
The repair process
- Break out. Damaged concrete is removed back to sound material and behind the corroded steel.
- Treat the steel. Reinforcement is cleaned of rust and coated with a corrosion-inhibiting primer. Badly corroded bars may need to be supplemented.
- Reinstate. The section is rebuilt with a repair mortar suited to the depth and location.
- Protect. The area is finished and coated so it blends with the façade and resists further water entry.
- Seal the cause. Cracks, joints and sealant that let water in are repaired at the same time.
Fixing the water source
Many concrete cancer repairs fail because the water that caused them is never dealt with. These are the common sources and fixes:
| Area | Typical issue | Fix |
|---|---|---|
| Window frames | Failed perimeter sealant | Sealant replacement |
| Balcony edges | Ponding water, cracked edges | Repair, drainage review, protective coating |
| Walls | Cracks letting water in | Crack repair and recoating |
| Joints | Failed expansion joint sealant | Joint resealing |
Why rope access suits concrete repairs
Concrete cancer is usually spread across a façade in small patches rather than in one area. Rope access lets technicians reach each patch directly, without scaffolding the whole building to repair a handful of balcony edges. The same setup can be used for sealant, crack repairs and painting so the façade is left watertight and finished.
Prevention
- Inspect the façade every one to two years, more often on the coast
- Repair cracks and replace failed sealant early
- Keep balcony drains clear and check falls
- Maintain the protective coating rather than waiting for it to fail
FAQs
Is concrete cancer dangerous?
It can be. The main risk on multi-storey buildings is loose concrete falling. It also weakens the affected element over time if left untreated.
How much does concrete cancer repair cost?
It depends on the number and depth of repairs and the access required. A mapped inspection is the best way to get a reliable scope and price.
How long does a repair take?
Isolated repairs can be completed in days. Larger programs take longer, partly because repair mortars and coatings need curing time.
Can you just patch over it?
Patching over corroded steel without treating it usually fails within a few years. The steel needs to be exposed, cleaned and protected.
Seeing cracks, rust stains or falling concrete? Ace Abseiling carries out concrete cancer repairs by rope access across Sydney. Request an inspection and send us photos of the affected areas.
