How to Patch Concrete: Cracks, Spalling, and Surface Repair (2026)

Frequently Asked Questions

Do I need to widen a crack before patching?

For cracks under 1/8 inch: a flexible concrete repair caulk can fill them without widening. For cracks over 1/8 inch: yes, widening is important. A narrow crack has nearly no mechanical grip for the patch material — the patch is just sitting in a slot and will pop out. Widening to 1/4 inch minimum (using a grinder or chisel) and undercutting the edges (making the bottom of the slot wider than the top) gives the patch something to grip. This is called keying the repair and it makes the patch last years instead of weeks.

What is the difference between concrete patch compound, hydraulic cement, and crack filler?

Concrete patch compound (Quikrete Vinyl Concrete Patcher, Sakrete Top 'N Bond): polymer-modified cement mix. Best for surface spalling, shallow repairs, and wide crack filling. Bonds well to existing concrete. Hydraulic cement: sets and expands while wet — used for active water leaks in concrete (pools, foundation walls, wet basement walls). It sets in 3–5 minutes so it can be held in place against water pressure. Concrete crack filler (liquid or caulk-type): best for hairline cracks and joints where some flexibility is needed. Not for structural repairs or load-bearing surfaces.

My concrete driveway has a crack that opens in summer and closes in winter. Can I patch it permanently?

No — a crack that cycles with temperature is a moving crack. A rigid patch will crack again when the concrete moves. The correct repair: clean the crack, apply a [self-leveling polyurethane sealant](https://www.amazon.com/s?k=self+leveling+polyurethane+concrete+crack+sealant&tag=fixupfirst-20) or a backer rod plus flexible sealant. These materials move with the concrete instead of cracking. Rigid patch compounds do not work on moving cracks.

The concrete surface is flaking and crumbling (spalling). Can I resurface it?

Yes — concrete resurfacer (Quikrete Concrete Resurfacer, Ardex Feather Finish) can restore spalled surfaces. Requirements: (1) The underlying concrete must still be structurally sound (no deep cracks, soft areas, or widespread delamination). (2) All loose material must be removed by pressure washing, wire brushing, and grinding. (3) The surface must be clean and damp (not wet) at application. Resurfacers can be applied as thin as 1/8 inch and will bond to properly prepared concrete. Not suitable for surfaces that have been contaminated with oil — oil prevents bonding.

How important is curing time for concrete repairs?

Critical. Concrete and concrete repairs cure by hydration — a chemical reaction that requires water. If the patch dries out too fast (hot sun, wind, low humidity), the reaction stops early and the patch will be weak and crumbly. Keep the repair moist for at least 3 days: mist lightly with water and cover with plastic sheeting. For repairs under 1/4 inch thick: be especially vigilant about curing because thin patches dry out quickly. Concrete repair products that say 'ready in 1 hour' mean ready for light use — full cure takes 28 days.

For cracks in concrete: surface-widen the crack to at least 1/4 inch (use an angle grinder with a diamond blade, or cold chisel and hammer) to create a keyed channel the patch can grip. Clean out all loose material and dust.

Concrete patch repairs that fail usually failed in the prep, not the material.

What you need

• Concrete patch compound (Quikrete Vinyl Concrete Patcher or similar)
• Concrete crack filler (for hairline/moving cracks)
• Cold chisel or angle grinder with diamond blade (to prep cracks)
• Wire brush and shop vacuum
• Bucket and trowel or margin trowel
• Plastic sheeting (for curing)
• Concrete bonding adhesive (optional, for deep repairs)

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Step 1: Prepare the damaged area

Cracks: Use a cold chisel and hammer (or angle grinder with diamond blade) to widen the crack to at least 1/4 inch. Undercut the edges so the bottom of the groove is wider than the top — this keys the patch in place.

Spalled surface: Remove all loose, flaking concrete with a wire brush, hammer, and cold chisel. Any concrete that sounds hollow when tapped must be removed — it has already delaminated. Grind or chisel until you reach solid material.

Vacuum all debris. Clean with water and let the excess dry so the surface is damp (not wet or dry).

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Step 2: Mix the patch compound

Mix the concrete patch compound per the package ratio — typically just water. Consistency: thick peanut butter. Let it slake 5 minutes, stir again.

For deep repairs (over 2 inches): build up in layers, letting each layer firm before applying the next.

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Step 3: Apply bonding adhesive (optional but recommended)

Apply a thin coat of concrete bonding adhesive (liquid latex) to the prepared area with a brush. Let it get tacky (5–10 minutes). This improves adhesion significantly for any repair thicker than 1/4 inch.

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Step 4: Apply the patch

Press the patch compound firmly into the prepared area with a trowel. Work it into the crack or against the sides of the spalled area to eliminate voids.

Smooth the surface with a finishing trowel. Feather the edges — don’t leave a sharp bump. Match the texture of the surrounding concrete as closely as possible (a sponge float creates a broom-finish texture).

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Step 5: Cure

Cover with plastic sheeting immediately. Mist the repair with water, lay the sheeting over it, and weight the edges to prevent it from blowing off.

Keep moist for 3 days minimum. For full strength: keep covered for 7 days.

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Related guides

• How to Fix a Cracked Driveway — driveway-specific crack and surface repair
• How to Seal a Driveway — protective sealing after patching
• How to Seal a Concrete Floor — interior concrete floor sealing after repairs