How to Use Concrete Filler | Crack Fix That Lasts

A crack in your driveway or patio doesn’t mean a full replacement—concrete filler can seal it tight and keep water out for years. But the difference between a repair that lasts and one that crumbles in a season comes down to prep, depth control, and letting the correct product cure. Here is the exact method for each type.

Choose the Right Filler for the Crack

Concrete fillers vary by what they handle. Cement-based (acrylic or latex) fillers work for cracks up to ½ inch wide and bond well with damp concrete. Flexible polyurethane sealants are better for cracks that move with seasonal temperature changes—they self-level and stay elastic. For very deep or structural cracks, a two-part epoxy or composite repair mortar is the strongest option. If you need a fast comparison of the best products on the market, see our tested roundup of concrete fillers that covers which one fits your job.

Prep the Crack for a Solid Bond

Skipping prep is the number one reason filler fails. Start by clearing out all loose debris, dirt, and vegetation using a pressure washer, compressed air nozzle, or leaf blower. For cracks deeper than ⅜ inch, use a cold chisel and hammer to cut an inverted V-shape (wider at bottom, narrower at top) so the filler locks in place and won’t push out during freeze-thaw cycles. For some composite fillers, cut the crack to a U-shape at least 6 mm wide and 20 mm deep, avoiding any steel reinforcement. Dampen the crack with water for better adhesion with cement-based products, but remove any standing puddles—flooding washes the filler out.

For very deep cracks (over ⅜ inch), pack the bottom with mason sand or a foam backer rod so the filler sits only the top ⅜ to ½ inch deep. This prevents the filler from sinking and cracking later.

Apply the Filler Correctly

For one-part squeeze tubes, remove the cap and internal seal, cut the spout at a 45-degree angle for the bead size you need, and squeeze filler directly into the crack, slightly overfilling it. For cracks deeper than ¼ inch, fill in ¼-inch layers and let each layer cure 24 hours before adding the next—skipping this causes shrinkage cracks inside the repair. For two-part epoxy systems, mix Part A with cement and sand for 30 seconds, then add Part B liquid and mix for 1.5 minutes before troweling it in.

Level the surface with a putty knife, trowel, or gloved finger, feathering the edges flush with the surrounding concrete. For polyurethane sealants, apply slowly along the joint line from one end to the other—these are self-leveling, so resist the urge to overwork them.

Finishing and Curing

For cement-based fillers, lightly mist the area with a spray bottle or garden hose on mist setting to activate the cure. Do not flood the repair—excessive water washes the product out. Most latex and polymer fillers need 24 hours before foot traffic; some fast-setting products allow foot traffic in 30 minutes. If you overfilled and need to smooth the surface, sand with medium-to-coarse sandpaper after 24 hours. For polyurethane and epoxy fillers, let them cure naturally for 24 to 48 hours before heavy use. Common mistakes are overfilling (hard to remove cured excess), ignoring depth (causes filler to pop out in temperature cycles), and applying to a completely dry crack without dampening (reduces adhesion). Wear gloves if you have sensitive skin and eye protection when chiseling or using compressed air.