I just had a patio poured a month ago, and now it has a giant crack! What do I do about this crack in the concrete?!? Fear not. I will let you in on a little secrete. Not many people know this. All concrete cracks! I bet you didn’t expect that. But when does a crack become a problem?

In a previous post, we discussed construction techniques to keep concrete from cracking. Today, we are discussing how to repair a crack on an existing concrete surface.

When A Crack is a Problem

First, do some investigation to determine what caused the crack. The most common cracks are shrinkage cracks that occur during the curing process. As concrete cures, it shrinks approximately 1/4-inch per 30-ft resulting in shrinkage cracks. Ideally, these cracks should be contained within the control joints. If the cracks are not contained within the control joints, further evaluation of the crack is necessary.

Crack width gauge for concrete
A transparent crack width gauge* to measure a crack width.

Cracks that are less than 0.013-in (or about the width of a credit card) are not susceptible to water penetrating into the concrete. Therefore, a crack width gauge* should be used to measure the width of the cracks. Cracks outside of the control joints and greater than 0.013-in should be repaired.

Before I discuss repair procedures, contact a professional if any of these situations are present:

  • There are multiple cracks throughout the section of concrete. This signifies a potential major underlying issue that requires further analysis.
  • The crack(s) is growing. If the crack continues to widen with time, the underlying issue must be addressed before any repair can be made. If you are not sure if the crack is growing, install a crack monitor* to verify.
  • Orange rust stains are visible. This can signify the rebar (steel reinforcing) is corroding. As steel corrodes, it expands, causing even more cracking in the concrete surrounding it. The rusting rebar has to be addressed by a professional.
  • The cracks are present on a structural element, such as a basement wall, column, beam, or retaining wall greater than 4-ft.
  • The crack is greater than 1/2-inch. If you know the issue that caused the crack and have addressed it, a professional may not be necessary. Examples include cracks from tree roots from a tree that has been removed, a collapsed pipe that has since been filled with concrete, or a washout where the undermined material has been replaced and the drainage issue that caused the washout has been addressed.

If none of these are true, then the crack can likely be repaired without a professional.

Repair for Cracks on Horizontal Surfaces

Horizontal concrete surfaces include patios, sidewalks, driveways, and slabs. For cracks less than 1/2-inch, use a low viscosity epoxy adhesive. I recommend PC-Concrete Two-Part Epoxy Adhesive* for cracks that do not extend through the entire concrete thickness. For cracks that do extend entirely through the concrete, follow the steps for cracks on vertical surfaces.

Less than 1/2-inch wide cracks:

For cracks less than 1/2-inch, use a low viscosity epoxy adhesive. I recommend PC-Concrete Two-Part Epoxy Adhesive* for cracks that do not extend through the entire concrete thickness. For cracks that do extend entirely through the concrete, follow the steps for cracks on vertical surfaces.

  1. Clean the crack with a brush. If available, blow compressed air into the crack.
  2. Remove the cap on the epoxy tube. Then, place the tube in the caulk gun*.
  3. Squeeze out some of the two-part epoxy until the each part is mixing evenly.
  4. Install the nozzle. Next, inject the epoxy into the crack. Ensure the crack is fully filled.
  5. Put on gloves. Then use a trowel to smooth out the epoxy. To get a really smooth finish, dip your finger into denatured alcohol* (with gloves on) and smooth the epoxy with your finger. The denatured alcohol does not stick to the epoxy. Wipe any excess epoxy onto a paper towel.

Greater than 1/2-inch wide cracks

For cracks wider than 1/2-inch, or small spalls in the concrete, use a two-part epoxy paste*:

  1. If the damaged surface is smooth, roughen the surface with a chisel. This will help bond the epoxy to the concrete.
  2. Clean the crack or spalled area with a brush. Blow compressed air into the crack.
  3. Thoroughly combine the two epoxy pastes on a flat plastic surface until they are fully mixed. This process takes a couple minutes.
  4. Apply the epoxy past with a trowel.
  5. Shape the epoxy past with a trowel. For a more exact finish, put on gloves and dip your gloved finger in denatured alcohol. Use your finger to apply the finishing touches. Epoxy paste typically hardens within a couple hours.

Repair for Cracks on Vertical Surfaces

Vertical concrete surfaces include retaining walls, basement walls, and foundation walls. As noted above, contact a professional for a structural component of your house and for retaining walls greater than 4-ft in height. The below procedure should be followed for cracks on vertical surfaces or cracks that penetrate the entire thickness of the concrete.

  1. Clean the crack with a brush. If available, blow compressed air into the crack to clean it out.
  2. Apply capseal to the back of the injection ports. Place the injection ports along the crack. Space the injection ports 1.5 times the depth of the crack. Note, the capseal dries very quickly. Only apply capseal on 1-2 inject ports before installing them on the crack.
  3. Place capseal along the entire crack between injection ports. Use the capseal to seal around the injection ports. Allow the capseal to fully cure before injecting resin.
  4. Inject the epoxy resin into the injection ports, starting with the bottom most injection port.
  5. Allow the epoxy resin to cure. Then remove the capseal. Use a chisel or grinder. If necessary, repair the surface of the concrete with two-part epoxy paste using the steps as described above for cracks greater 1/2-inch.

Here is a more detailed video for vertical cracks utilizing the product I recommend: Sikadur Crack Repair Kit*.

Sikadur Crack Repair Kit* for vertical surfaces.

Those are the basic ways to repair a crack in concrete. As I mentioned above, do not attempt to repair a crack that requires a professional. Please leave any questions or feedback in the comments below.

*Amazon Affiliate – If you use these links and make a purchase, I may be compensated.