Concrete Spalling: Causes, Warning Signs and Repair in South Florida
Short answer: Concrete spalling is when the surface of concrete cracks, flakes or breaks away. In South Florida it's usually caused by corroding rebar: salt air and moisture reach the steel inside the concrete, the steel rusts and expands, and the expansion forces the surrounding concrete apart. Spalling should be evaluated by a structural engineer and repaired by a licensed contractor, not just patched.
What causes concrete spalling?
Reinforced concrete is strong because of the steel rebar inside it. Normally, the concrete around the rebar protects it from corrosion. Over time, water and chlorides from salt air work their way into the concrete through cracks, failed coatings and failed sealants. Once they reach the steel, it begins to rust.
Rust takes up more space than the original steel — as rebar corrodes, it can expand to several times its original thickness. That expansion creates pressure inside the concrete until the concrete cracks and pieces break off.
Other contributors include:
concrete that was placed with too little cover over the rebar
cracks that let water in
failed waterproofing on balconies and walkways
ponding water that sits on the surface
Why is spalling so common in South Florida?
South Florida combines three things concrete doesn't like: salt air, high humidity and heavy rain. Coastal and near-coastal buildings are exposed to chlorides every day, and many condominiums have exposed balconies, catwalks and slab edges that take the brunt of the weather.
What are the warning signs of concrete spalling?
Cracked, bulging or broken-off concrete on balconies, walkways, columns or slab edges
Rust stains bleeding through concrete or stucco
Exposed or visibly rusted rebar
Cracks around railing posts or along balcony edges
Hollow sounds when the concrete is tapped
Leaks into units or garages below
Is concrete spalling dangerous?
It can be. Spalling means the reinforcing steel is losing strength, and loose concrete can fall. Early spalling on a balcony edge may be a relatively small repair; widespread spalling on structural members is a serious problem. Either way, it should be evaluated by a structural engineer — and in Florida, it's one of the conditions milestone inspections look for.
How is concrete spalling repaired?
A proper spall repair treats the cause, not just the surface. A typical engineer-specified repair includes:
Removing deteriorated concrete around the damaged area, including behind the rebar
Cleaning the rebar of all corrosion — or replacing or supplementing steel that has lost too much section
Treating the steel with protective coatings as specified
Restoring the concrete with repair mortars or concrete matched to the engineer's specifications
Waterproofing and coating the repaired area so water can't get back in
The engineer of record typically inspects the exposed conditions before the area is closed up.
Why not just patch it?
A cosmetic patch over corroding rebar hides the problem. The steel keeps rusting underneath, and the patch usually fails — often taking more concrete with it. That's why the waterproofing and coating steps matter as much as the concrete repair itself.
See our Concrete Restoration and Waterproofing pages.
Concrete Spalling FAQ
Can spalling be repaired without an engineer?
For condominium and commercial buildings, structural concrete repairs should follow a structural engineer's evaluation and specifications, and typically require permits.
Will painting stop spalling?
No. Paint can't stop rebar that is already corroding. Repairs have to come first; protective coatings and waterproofing then help prevent new damage.
How long does a spall repair last?
It depends on the repair method, exposure and maintenance. Repairs that remove all corroded concrete, treat the steel and are protected by waterproofing and coatings last far longer than surface patches.
Does homeowners' insurance cover spalling?
Spalling from long-term corrosion is generally considered maintenance. Check with your association's insurance agent.
Seeing cracks or rust stains on your building? Request a free concrete restoration estimate: contact us or call 954-982-8165.
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