Rebuilding spalled concrete where the surface popped off

Concrete spall repair fixes spots where the surface of a slab has broken away. A spall can be a shallow flake the size of a coin or a crater several inches across. Common causes are water getting into the surface and freezing, deicing salt, a weak top that was overworked when the slab was troweled, rusting rebar or wire mesh too close to the surface pushing the concrete off, and hard impacts from dropped equipment. Once a spot starts, wheels and weather keep chipping at the edges and it grows.

Resurfacing covers a whole worn floor with an overlay.

The repair goes in a set order. We saw-cut a clean border around the damage so the patch doesn’t end in a feathered edge that breaks off, then chip out everything loose down to sound concrete. If rusty steel shows, it gets cleaned and treated. The hole is vacuumed, primed and rebuilt. Shallow spalls under a coating get an epoxy mortar, a sand-and-resin mix that’s harder than the concrete around it and grinds flush. Deeper or outdoor repairs often get a polymer-modified patch mortar, which moves more like concrete. Once it’s cured, the patch gets ground level so the floor reads as one surface.

Spall repair is spot work. Crack repair fills cracks. Joint repair rebuilds the broken edges along sawcut joints, which is a specific kind of spalling with its own fix. If spalls are scattered all over a slab, a full resurface may make more sense than patching thirty holes, and we’ll tell you which way we’d go.

Most of the Antelope Valley sees only occasional freezes, but they do happen, usually on clear winter nights. Water that soaks into a porous garage apron or patio, then freezes, expands and pries the surface apart a little at a time. Add the big temperature swings of every day out here and weak surface concrete breaks loose sooner than it would somewhere milder.

Toward the mountains at the edge of our range, freeze-thaw is a regular winter thing, and cars bring road salt and ice melt into the garage on their tires. Salt soaks into concrete and speeds up spalling, especially at the front of the garage where the car drips. A coated floor keeps water and salt out of the slab, so rebuilding the spalls and coating over them is the fix that holds.

Living with it

Sweep out sand and ice melt residue instead of letting it sit, especially in winter. If you use deicer near the garage, pick one labeled safer for concrete and rinse it off coated floors. Keep an eye out for new hollow or flaking spots and get them fixed while they’re small.