Concrete Curb Repair and Replacement

What actually broke, and why

Before you buy anything, figure out the cause. A patch that ignores the reason for the damage falls out the next winter.

• Freeze-thaw and de-icing salt. Water soaks into the surface, freezes, expands, and flakes the top layer off. Family Handyman notes that de-icing salts make this worse, which is why curbs in snow country spall first. This surface flaking is called spalling.
• Vehicle impact. A tire climbing the curb or a plow blade catching the edge shears off chunks. This is the most common reason a section breaks clean off.
• Frost heave and settling. The base under the curb shifts, and the concrete cracks because it has nothing solid to bridge across.
• Tree roots. A root under or beside the curb lifts and cracks it over a few seasons.

Spalling and small chips are surface problems. Full-depth cracks that have shifted, or a section that has broken off and dropped, are structural. That split decides your whole approach.

Repair or replace

Use a simple rule. Repair when the damage is isolated and the base is still sound. Replace when the damage is widespread or the ground under it has failed.

Cojo Asphalt puts the tipping point at damage over 25% of the length, or when a repair would cost about 60% of what full replacement costs. At that point you are paying twice for the same foot of curb.

How to patch a spalled or chipped curb

This is the everyday fix and the one most homeowners can do.

1. Clean and undercut. Chip out all loose and flaking material with a cold chisel and hammer until you hit solid concrete. Undercut the edges slightly, meaning cut them so the hole is a little wider at the bottom than the top. That lip locks the patch in. Wire-brush and rinse the area so no dust is left.
2. Wet it and prime. Dampen the old concrete (damp, not puddled) and brush on a bonding agent. A cement-and-water slurry or a product like QUIKRETE Acrylic Fortifier both work. This is the step people skip, and it is why patches pop off.
3. Pack the repair mortar. For chips and edges, a fast-setting repair mortar or vinyl concrete patcher goes in with a margin trowel. QUIKRETE's edge method mixes quick-setting cement with fortifier to a stiff putty, then presses it into the damage.
4. Shape it. Match the curb's profile. Once the mix is thumbprint-hard, usually 5 to 10 minutes for a fast set, mold the face and top to line up with the sound curb on either side.
5. Cure it. Keep it damp. Cover with plastic for a few days or mist it, and keep traffic off. Curing slow is what makes the patch last.

For a broad spalled surface rather than a hole, a thin concrete resurfacer is the better product. You clean, prime, and spread a stiff sand-and-cement overlay across the whole face, then cover with plastic for about five days per Bob Vila.

Fixing a crack

For a crack narrower than about a quarter inch, chase it open slightly with a grinder or chisel so you have something to fill, blow the dust out, and work in a concrete crack filler or a fortified patch. A masonry crack sealant that stays flexible handles the seasonal movement better than a rigid patch on a curb that still flexes a little. Wider cracks where the two sides sit at different heights are not really a crack problem. The base moved, and you are back to forming and repouring that section.

Rebuilding a broken section with a form

When a chunk has broken clean off, you rebuild it with a form so the new concrete holds the right shape.

1. Saw-cut the broken area back to solid curb. Contractors cut roughly 24 inches past the visible damage on each side so they are not bonding to more cracks.
2. Break out the failed piece and check the base. If it is soft or washed out, tamp in new gravel and compact it. A patch over a bad base fails again.
3. Drill and epoxy short rebar dowels into the cut ends of the old curb so the new pour is tied in. Pros use half-inch (#4) dowels; on a small residential curb a couple per joint is plenty.
4. Build a form from plywood or dimensional lumber that matches the curb's height and face. Brace it well so it does not bow when you fill it.
5. Brush a bonding agent on the old cut faces, then place a stiff 4,000 PSI mix. Rod it to remove voids, screed the top, and tool the exposed edge.
6. Match the finish (usually a broom or light float), then cure with plastic or a curing compound and keep traffic off for about 7 days. Full strength comes at 28 days.

If you are mixing your own bags for this, the concrete curb calculator tells you how many you need, and the pouring guide walks through forming and finishing in more detail.

Cutting or lowering a curb for a driveway

If your goal is not repair but concrete curb cutting, meaning lowering the curb to add or widen a driveway, stop before you touch it. The curb along the street is almost always in the city or county right-of-way, not on your property, even though it sits at the edge of your lot. Cutting it without approval can mean fines and a bill to put it back.

You need a curb cut or driveway permit from your city. Seattle, for example, requires a curb cut permit with a site plan before any work happens, and most cities run a similar process. The permit sets the width, the apron slope, and drainage so the new opening does not pond water or block the gutter line. Many cities also require the work be done by a licensed contractor. Call your public works or transportation department first.

Materials table

Sources

• Cojo Asphalt: How to Repair Broken Concrete Curb (2026)
• Family Handyman: How to Fix Spalling Concrete
• QUIKRETE: Repairing Concrete Edges and Corners
• Bob Vila: What to Do About Spalling Concrete
• Engineer Fix: How Much Does Curb Repair or Replacement Cost?
• Seattle SDCI: Curb Cut Permit