Spalling and Scaling: Why Concrete Surfaces Flake and How to Fix Them

Not all concrete damage starts with a crack. Sometimes the surface itself begins to break down: a thin layer flakes away and exposes the sand and stone underneath, or pieces pop out and leave rough craters. Homeowners often call all of it chipping, but two different problems are involved, and telling them apart is the first step toward the right repair.

Scaling is the loss of the thin top layer of concrete, usually only a fraction of an inch deep. It shows up as patches where the smooth surface has worn away to reveal sand and small aggregate. The cause often traces back to the day the concrete was placed: water sprinkled on the surface to make finishing easier, finishing while bleed water was still on top, or a slab that dried out too fast without proper curing. Each of those leaves a weak top layer that wears and flakes under traffic and weather. In colder climates, deicing salts are a major cause. In Central Texas, where freezes are less frequent, finishing and curing problems are the more common source.

Spalling goes deeper. Larger pieces break away, and the damage can reach the reinforcing steel. A frequent cause is rebar or wire mesh that sits too close to the surface. As the steel rusts, it expands and pushes the concrete above it off, so you may see rust staining or bare metal at the bottom of the spall. Impact, heat from grills or fires, and small aggregate particles that react with moisture and pop out (known as popouts) can also cause surface loss.

Diagnosis starts with a few simple observations. How large is the damaged area compared with the whole slab? Is it confined to a walking path, the spot below a downspout, or the place where a grill used to sit? Is it getting bigger? Tap the surrounding concrete with a hammer or steel rod. A hollow sound means the top layer has separated from the concrete below, a condition called delamination, and the damage may be larger than it looks.

Repairs range from simple to major. A small, isolated spall can be cleaned out, its edges squared up, and filled with a bonded repair material made for concrete. Where steel is exposed, the rust has to be removed and the bar treated or replaced before patching; otherwise the corrosion keeps going under the repair. Widespread scaling on an otherwise sound slab is often a good candidate for resurfacing with a bonded overlay, which restores a uniform surface without tearing out the concrete. When delamination is extensive, steel is corroding throughout, or the slab is also cracked and settled, replacement usually makes more sense.

Prevention depends on the cause. Keep water from sitting on the surface by fixing drainage problems and directing downspouts away. Apply a quality sealer to reduce water absorption, and reapply it on schedule. Keep grills and fire pits off bare concrete. For new work, ask how the crew finishes and cures the slab, because those details decide whether the top layer is as durable as the rest.

Not sure whether the damage on your slab is surface-deep or a sign of something underneath? CIMA Concrete repairs spalled and scaled concrete, resurfaces worn slabs, and replaces sections that are beyond repair for homes and businesses around Lockhart.