Filling a concrete crack is a quick DIY repair: clean loose debris out of the crack, widen it slightly if needed so the filler can grip, then pack in a concrete crack filler or sealant and smooth it flush. Repairing cracks early matters in Houston because water gets into them, and as our clay soil swells and shrinks — plus the occasional freeze — that water pries the crack wider until a hairline becomes a trip hazard or a broken slab. For cracks up to about a half inch wide, a tube of crack sealant handles it. Wider or displaced cracks need a patching compound or a pro.
What you'll need
- A hammer and cold chisel (for wide cracks)
- A wire brush
- A shop vacuum or compressed air
- A caulking gun
- A putty knife or trowel
- A garden hose
Recommended parts & supplies
- Concrete crack filler / sealant — self-leveling for horizontal cracks, in a caulk-gun tube
- Concrete patching compound — for wider or deeper cracks that a sealant can not fill
- Wire brush — scours loose material out of the crack
- Concrete driveway sealer — seal the repair and surrounding slab afterward
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Step by step
- 1
Clean loose debris out of the crack
Use a wire brush to scrub the inside of the crack, then blow it out with compressed air or a shop vacuum to remove every bit of loose concrete, dirt, and old filler. Filler bonds to solid concrete, not to grit — so this cleaning step is what makes the difference between a repair that lasts and one that pops out in a month.
- 2
Widen and undercut a wider crack if needed
For cracks wider than a pencil, use a hammer and cold chisel to knock away crumbling edges and, if you can, undercut the crack so it is slightly wider at the bottom than the top. This keys the filler in place so it can not lift out. Vacuum again after chiseling. Hairline cracks do not need this — skip straight to filling.
- 3
Rinse and let it dry (or follow the product)
Some fillers want a clean, dry crack; a few are designed to go into a slightly damp one. Check your product. For most crack sealants, give the crack a rinse to flush the last dust, then let it dry fully — important in humid Houston, where concrete holds moisture longer than you expect.
- 4
Fill the crack with sealant or compound
For narrow cracks, load the crack sealant tube into a caulking gun and run a steady bead down the full length, pushing it into the crack rather than just laying it on top. For wider or deeper cracks, press a concrete patching compound in with a putty knife, packing it down so there are no air pockets. Slightly overfill, since fillers tend to settle as they cure.
- 5
Smooth it flush and tool the surface
Drag a putty knife or trowel across the filled crack to level it flush with the surrounding concrete. For self-leveling sealants, it will settle on its own — just knock down any high spots. If you want the patch to blend, you can texture the surface lightly to match the broom finish of the driveway before it skins over.
- 6
Let it cure, then seal over the repair
Give the filler the full cure time on the label before walking or driving on it — anywhere from a few hours to a full day. Once cured, sealing the whole driveway over the repair protects it and helps the patch blend in. Keeping water out of the repaired crack is what stops it from reopening the next time the soil moves.
When to call a pro
Call a concrete contractor when the crack is more than a symptom. Cracks wider than about a half inch, cracks where one side sits higher than the other, cracks that keep widening after you fill them, or a network of cracks across a whole slab all point to soil movement or a failing base underneath — filling those is a temporary cosmetic fix at best. The same goes for cracks running through a large driveway or a slab that has visibly sunk or heaved. Those situations need a pro to evaluate the subgrade and decide whether the section should be repaired, mudjacked, or replaced.
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How to Fill and Repair a Concrete Crack (DIY Driveway Guide) — FAQ
What is the best filler for a concrete driveway crack?
Why do cracks in my Houston driveway keep coming back?
Should I seal the driveway after filling a crack?
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