Concrete spalling is when pieces of concrete flake, crack or break away from the surface. It is common on balconies, slab edges, carparks, columns and beams across Sydney, and it is usually a sign of something happening inside the concrete.
What causes concrete spalling?
Corroding reinforcement
The most common cause. Steel inside concrete is protected by the alkaline concrete around it. Over time, carbonation or chlorides from salt air reduce that protection, and moisture lets the steel rust. Rust takes up more space than steel, so it pushes the concrete apart and breaks off the surface. This is what most people call concrete cancer.
Thin cover to the steel
Steel placed too close to the surface during construction corrodes sooner. This is common in older apartment buildings.
Water and leaks
Failed balcony and roof waterproofing keeps concrete wet, speeding up corrosion.
Other causes
Impact damage, poor finishing, and fire can also cause surface spalling.
Why spalling must be repaired
- Falling concrete is a safety risk to people below.
- The steel keeps losing strength as it corrodes.
- Damage spreads with every wet season, making repairs larger and more expensive.
How to fix spalling concrete properly
- Find every affected area, including hollow, delaminated concrete found by tapping.
- Break out damaged concrete back to sound material and behind the corroded steel.
- Clean and treat the steel, and add new bars where too much has been lost.
- Rebuild the section with repair mortar or new concrete to the engineer's specification.
- Protect it with coatings, and fix the waterproofing that let water in.
Why patches fail
Patching over spalling without removing all the damaged concrete and treating the steel traps the corrosion inside. The patch usually cracks off within a few years, often taking more concrete with it.
Spalling concrete repairs in Sydney
See our concrete repair service or our guide to concrete cancer repair cost.
Frequently asked questions
What does concrete spalling mean?
It means pieces of concrete flaking or breaking away from the surface, usually because steel reinforcement inside is corroding and expanding.
Is spalling the same as concrete cancer?
Spalling is the visible damage. Concrete cancer is the common name for spalling caused by corroding reinforcement, which is the most common cause.
Can you just patch spalling concrete?
Patching without removing damaged concrete and treating the steel usually fails. The repair must deal with the corrosion.
