Concrete spalling is the flaking, chipping, or breaking away of the surface layer of concrete, usually caused by trapped moisture, corroding rebar, or freeze-thaw damage.
Understanding Concrete Spalling
Spalling is what happens when the surface layer of a concrete slab breaks away, leaving behind chipped, pitted, or flaking patches. It can range from small surface pockmarks to larger sections that come loose entirely, and it is one of the most common issues contractors are called in to repair before any coating can go down.
What Causes Spalling
Freeze-thaw cycles are a leading cause, since water that seeps into the concrete expands as it freezes and pushes the surface apart from the inside. Corroding rebar is another major cause, since rusting steel expands and cracks the concrete covering it from within. Deicing salts, poor original finishing, and low-quality concrete mix design can all accelerate the problem as well.
Identifying Spalling Before It Spreads
Early spalling often starts as small surface pits or hairline cracks that widen over time, so catching it early makes repair far simpler than waiting until large sections have broken loose. Sounding the slab by tapping it and listening for a hollow response can help identify delaminated areas that have not yet visibly failed.
Repair Approaches Before Coating
Spalled areas typically need to be chased out to sound concrete, cleaned, and patched with a repair mortar or epoxy-based patching compound before any coating system goes over the top. Skipping proper spall repair and coating directly over damaged concrete almost always leads to the coating failing in that same spot again, since the underlying problem was never fixed.
