How To Repair And Seal Cracks in Concrete

A guide for repairing concrete damage.

Cracks in concrete aren’t just an eyesore. They pose a hazard for tripping, and will result in more damage down the line. Cracks allow in water, water expands and contracts over the course of a day/year. This change in volume causes cracks to expand and causes all kinds of other types of damage. Broken out pieces, rutting, and uneven surfaces can all happen to concrete. Repairs will keep damage from spreading and getting worse. Fortunately, we’ve got a handy guide for repairing damage and cracks.

Required tools and materials

  • A tub/bucket for mixing the concrete sealant.
  • Two trowels/floats.
  • Paint brush.
  • A chisel.
  • Hammer/sledgehammer (depending on the size/depth of the crack).
  • Concrete product. This can be epoxy/latex or a mortar mix. These mixes can be called filler, sealer, and more. They vary differently according to the size and requirements of the repair job.

Mortar mix is made from:

  • Portland cement
  • Vinyl
  • Sand
  • Water


Optional:

  • Stiff fiber brush/ wire brush
  • Putty knife (for more delicate/detailed work).

Step 1

Choose your concrete repair product. There are many. You should NOT fill a concrete crack with more concrete. You will need something to fill the patch and something to seal it afterwards.

Products include:

  • Concrete sealant
  • Ready-mix concrete
  • Patching compound
  • Vinyl patch repair
  • Epoxy
  • Latex
  • Polymer structural concrete repair product
  • Self-leveling sealant

And much more. You can even by full-on kits that have just about everything you need. Choosing the right product is important, and based on a few considerations. A marine environment will require a heavy-duty seal that won’t be damaged by salt water. Structural repairs may require their own special mixtures. Light/surfaces scratches or cracks can sometimes get by with epoxy/resin mixtures. For this guide, we are assuming you are fixing outdoor concrete for general business/home use.

For general outdoor concrete repairs, you can use the following two fillers:

  • Epoxy/latex for cracks whose width is 1/8 an inch or less.
  • Mortar mix is best for larger imperfections. Big cracks and full-on holes will require mortar mix. The surface can be covered with a sealant after the main repair is complete.

Step 2

This may seem counterintuitive, but you will start by making the crack bigger. Use the chisel to make the crack wider at one side than at the other. The crack should be shaped like a carrot or daikon. The main area to be filled should be the widest. The narrow area helps to anchor the filler by providing more contact area per filler volume.

Widen the crack at the top by using your chisel and hammer. If the crack is shallow, chip away until it is about 1 inch below the surface of the plane of concrete. If the crack is especially deep, or the concrete is especially hard, you may need a sledge hammer instead. Lightly tap the chisel with the sledge hammer so you don’t accidentally do too much damage. You should also make sure to remove large loose rocks from the crack with your hammer/chisel. 

Step 3

Use your paintbrush to clean out the crack. Every small pebble and shard of loose concrete weakens the fillers grip on the inside of the crack. They take away from purchase area, and they weaken the sealer itself. Ideally your crack will have nothing but filler when it is repaired. You can use also use the stiff fiber/wire brush if the paint brush and your fingers aren’t enough for the job.

Step 4

Inexperienced people working on their homes, and sometimes even paving contractors who like to cut corners will treat this as step 1. Additionally, people will often simply use more concrete to fill the crack. This will not result in as secure and permanent a repair as using the proper product.

Using epoxy/resin in small cracks

For 1/8 an inch or less width cracks, use your epoxy/latex mix. Before use, you may have to mix the two substances. Be sure to follow the manufacturer’s guide on what ratio to use. Use the trowel to force the mix into the crack. You may prefer using a putty knife for this. After the crack has been filled, smooth it so it is level with the surrounding concrete. Afterwards, consult the directions on the packaging again so you know how long it will take to cure. It may need to be covered during the curing process.

Using a mortar mix in large Cracks

Mix your Portland cement, vinyl, and sand. Use as little water in the mix as possible. Blend 1 part Portland cement to 3 parts sand. A ready-mix will have the Portland cement and sand already combined. Mix 1 part water to 3 or 4 parts mix. Make sure the mortar mix is not too thick and not too runny. Stir for 5-10 minutes and let it rest 10 minutes before stirring again. The process should take at least 2 hours.

Now it’s time to fill the crack. Use the trowel to ensure the crack is completely filled. When filling with this substance, be sure to frequently press down on the area with the trowel to eliminate air bubbles. Once the crack is completely filled, make sure to level its surface with the trowel, so it is the consistent with the rest of the concrete. Let it sit for about 2 hours afterwards. Next, cover it with a plastic sheet to keep humidity levels high. Sprinkle water once per day over the next several days on the surface until it has fully hardened.

Does your asphalt or concrete need some love?

At Reliable Paving, cement, concrete, and asphalt is our bailiwick. We are consummate professionals when it comes to asphalt paving, concrete and asphalt repairs, striping, and seal coating. If you want your pavement fixed right the first time, come to us. Contact us today and we can get the job started — and finished, sooner.