Spalling is when the surface of concrete flakes, chips, or breaks away, leaving rough, pitted patches. Common causes include freeze-thaw cycles, deicing salts, poor finishing when the slab was poured, and rusting rebar inside the concrete. It’s especially common on slabs exposed to winter weather. Spalled areas usually need repair before any finish or coating goes down.
What Does Spalling Look Like on Concrete?
Spalling can be as small as a few shallow chips the size of a coin or as big as a patch where the top layer has peeled away and exposed the stone underneath. You’ll often see it first along edges, near joints, and in spots where water or slush sits. Garage floors near the door and driveways where cars drip salty snowmelt are classic trouble spots.
A milder version, where just a thin skin of the surface flakes off, is often called scaling. Deeper breaks, especially ones with rust stains, point to rusting steel inside the slab.
What Causes Concrete Spalling
Most spalling starts with water. In cold climates like Wisconsin, water soaks into the surface, freezes, and expands, and repeated cycles break the top layer apart. This is freeze-thaw damage, and deicers make it worse by keeping the surface wetter through winter.
Other common causes include:
- A weak top layer from extra water added during finishing or from curing too fast
- Rebar or wire mesh that rusts and swells, pushing the concrete above it off
- Heavy impacts, such as dropped tools or plow blades
How Serious Is Concrete Spalling?
Surface spalling on a garage floor or patio is usually a cosmetic and comfort problem, not a structural one. It gets worse over time, though. Every chip gives water a new place to collect, so a few pits this winter can turn into a rough patch in a few years.
Spalling with rust stains, or on walls, columns, or balconies, is a different story. That can mean the steel inside is corroding, and it’s worth having an engineer look at it.
How to Fix Spalling Concrete
Small, shallow spalls can be patched. The crew removes loose material, cleans the area, and fills it with a repair mortar or overlay. Widespread or deep damage may call for resurfacing or replacing the slab.
On a floor that’s getting a finish, repair comes first. Coatings need a solid surface to grip, so a good contractor will grind off weak material, fill the pits, and then coat. Our guide to concrete floor coatings explains how that prep fits into the job.
Spalling FAQ
Will sealing concrete stop spalling?
Sealing helps prevent spalling by keeping water and deicing salt from soaking in. It won’t repair chips that are already there, and it won’t fix a weak surface. Patch or resurface the damage first, then seal or coat to protect it.
Is it worth repairing spalling concrete?
Usually, yes, if the slab is otherwise solid and level. Patching is far cheaper than replacement and stops the damage from spreading. If the slab is badly cracked, heaved, or spalled across most of its surface, replacement may make more sense.
How fast does spalling spread?
There’s no set speed. It depends on how much water the slab sees, how many freeze-thaw cycles it goes through, and how much salt hits it. In a snowy climate, untreated spalls can grow noticeably from one winter to the next.
Who is responsible for spalling concrete?
On new concrete, early spalling can point to finishing or curing problems, so check the installer’s warranty. On older slabs, it’s usually a maintenance issue for the owner. In condos or shared buildings, the association’s rules decide who pays.