Spalled Concrete Repair:
Causes, Methods
& Cost

Spalled concrete repair is mostly demolition. The patch material is the easy part; the work is finding every bit of delaminated concrete, cutting it out to sound material with square edges, and dealing with whatever caused the spall in the first place. Skip that, and the patch pops out with the next freeze or the next season of rust. This guide covers why concrete spalls, how to size up the damage, the repair sequence the industry uses, and what it costs.

Spalled concrete assessment tool

Enter what you measured at the worst spall. If steel is showing, the tool works out how deep you need to remove concrete: cover to the bar, plus the bar diameter, plus 3/4 in of clearance behind it (the ACI RAP 7 and TxDOT figure).

How to repair spalled concrete

This is the partial-depth repair sequence for a spall on a slab, step or deck, drawn from ACI RAP Bulletin 7 and the TxDOT intermediate spall procedure, with the field notes our applicators add.

1. Sound and mark

   Tap with a hammer or drag a chain over the whole area (ASTM D4580 is the chain-drag method RAP 7 cites). Outline every hollow area in paint and extend the outline into sound concrete.

2. Saw-cut a square perimeter

   Cut straight lines, at least 1/2 in deep per TxDOT, but never deeper than the cover over the steel, per RAP 7. Square shapes are easier to form and fill than ragged outlines.

3. Remove to sound concrete

   Chip out with a light chipping hammer, not a big breaker, so you do not fracture the concrete you are keeping. Where bars are exposed and corroded, remove concrete all the way around them with about 3/4 in of clearance, or 1.5 times the largest aggregate if that is more, per TxDOT. A practical check: you should be able to wrap your fingers around the bar.

4. Clean the steel and the cavity

   Blast the bars to remove rust. Profile the concrete to roughly a 1/8 in amplitude (CSP 6), which is also what SikaRepair-224 calls for. Blow out dust and debris.

5. Bring it to saturated surface-dry

   TxDOT soaks the cavity for at least 15 minutes. You want damp concrete with no standing water when the mortar goes in; a dry substrate pulls water out of the patch and kills the bond.

6. Place the repair mortar

   Scrub a bond coat of the mortar into the surface, then fill and compact. Build in lifts the data sheet allows; SikaRepair-224, a vertical and overhead mortar, lists 3/8 in to 2 in per lift on vertical surfaces. Extend horizontal mixes with clean pea gravel where the data sheet allows for deep holes.

7. Finish and cure wet

   Match the surrounding texture. Cure under wet burlap, polyethylene or a compatible curing compound. TxDOT asks for at least 72 hours; RAP 7 asks for at least 7 days on structural repairs.

Preventing the next spall

A spall repair fixes one hole. The chlorides and water that caused it are still in the slab around the patch, and that surrounding concrete is often next. Here is where we put our effort after the repair.

Where polyurea fits

We make polyurea and polyurethane coatings, and on structures with recurring corrosion spalls, a seamless elastomeric membrane over the repaired concrete is often the right final layer. It bridges fine cracks and blocks water and chlorides that a penetrating sealer only slows. Our corrosion prevention page covers those systems, and seawall repair covers the marine version of the same problem. A coating is not a substitute for the repair underneath, though. Coating over delaminated or rust-packed concrete just traps the problem.

On driveways and patios with widespread shallow scaling but few true spalls, it is often cheaper to patch the deep spots and put a bonded overlay over the whole slab. See concrete resurfacing for when that works. And if the spalled concrete also shows white crusty deposits, that is moisture moving through it; our guide to efflorescence explains what that means.