What You'll Need
- Concrete crack filler (hydraulic cement for wet areas, vinyl concrete patch for dry)
- Wire brush
- Shop vac or brush to remove debris
- Putty knife or margin trowel
- Spray bottle with water
- Safety glasses
- Work gloves
- Painter's tape (optional, for clean edges)
Step 1: Evaluate the Crack
Before patching, confirm this is a crack you should patch yourself.
Good candidates for DIY:
- Hairline cracks (less than 1/8 inch wide)
- Shrinkage cracks that haven't changed in at least 6-12 months
- Old repairs that have cracked or fallen out
- Cracks with no vertical displacement (both sides level)
Not good candidates:
- Cracks wider than 1/4 inch
- Cracks with one side higher than the other
- Cracks that are actively leaking water
- Cracks that have grown since you first noticed them
- Horizontal cracks in basement walls
If you're not sure, monitor the crack for a few months before patching. There's no point patching something that's going to crack again immediately.
Step 2: Prepare the Crack
Preparation determines whether your patch lasts or fails.
First, clean out the crack. Use a wire brush to remove loose concrete, dirt, and any old patching material. Get aggressive here. You want solid concrete on both sides of the crack.
For hairline cracks, you may need to widen them slightly so the patch material can penetrate. This feels counterintuitive, but a too-narrow crack won't hold filler well. Use a cold chisel or the corner of a putty knife to open the crack to at least 1/4 inch wide and 1/4 inch deep.
Vacuum out all the debris. Any dust or loose material prevents proper bonding.
Step 3: Dampen the Area
Concrete patch materials bond better to damp (not wet) concrete. Dry concrete sucks moisture out of the patch before it can cure properly.
Spray the crack and surrounding area with water. Let it soak in for a few minutes. You want the concrete damp but not dripping. No puddles in the crack.
For hydraulic cement, follow the product instructions exactly. Some brands want the area saturated, others just damp.
Step 4: Apply the Patch Material
Mix your patch material according to package directions. Most products want a thick, peanut butter consistency. Too thin and it runs out of the crack. Too thick and it won't bond well.
Force the material into the crack with a putty knife. Press firmly to eliminate air pockets. For vertical cracks, work from bottom to top.
Slightly overfill the crack. The material will shrink slightly as it cures. You can sand or scrape the excess once it's hard.
Material Options
Vinyl concrete patch: Good all-around choice for dry areas. Flexible, bonds well, easy to work with.
Hydraulic cement: Best for wet areas or actively seeping cracks. Expands slightly as it sets, creating a tight seal. Sets fast, so mix small batches.
Epoxy crack filler: Strongest bond, but more expensive and harder to work with. Usually overkill for cosmetic repairs.
Polyurethane caulk: Stays flexible, good for cracks that might move slightly. Won't match concrete color without painting.
Step 5: Smooth and Cure
Smooth the patch with your putty knife or trowel while the material is still workable. For walls, you want the patch flush with the surrounding concrete.
Follow curing instructions. Most patches need to stay damp for the first 24-48 hours. Cover with plastic or spray lightly with water periodically.
Don't paint or seal until the patch has fully cured, usually 7-28 days depending on the product.
Common Mistakes to Avoid
- Patching active cracks: If the crack is still moving, your patch will fail
- Skipping preparation: Dirty cracks won't hold patches
- Patching over paint: Remove paint around the crack first
- Using the wrong material: Water-seeping cracks need hydraulic cement
- Not addressing the cause: Drainage problems, settlement, etc. will cause new cracks
- Expecting perfection: Patches rarely match surrounding concrete exactly
What to Expect
A well-done patch on a stable crack should last years. My oldest patches are from 2014 and still look fine.
The patch won't be invisible. Concrete color varies, and patching materials rarely match perfectly. If appearance matters, plan to paint the wall with masonry paint after the patch cures.
If your patch cracks again within a few months, the underlying crack isn't stable. Stop patching and start monitoring or get a professional evaluation.