How To Fix and Repair Cracked Concrete

Repairing concrete cracks is a precise and delicate process. Reparation depends on the size and location of the crack. If the process is done improperly, it could lead to further deterioration of the concrete flooring.

However, with a steady hand and a few hours of time, you can fix most residential and commercial concrete cracks yourself. This is how to fix cracks in concrete.

Why does concrete crack?

Small hairline fractures in concrete can appear over time if the concrete wasn’t properly sealed. Concrete sealers help maintain surface durability and resistance. Without sealing, concrete is more exposed to friction, wear and tear, and external factors.

Larger concrete cracks often come from poor drainage conditions, water seepage, thermal movement, expansion, settling soil, or foundation cracking. If you have a significant concrete crack, especially if the crack appeared suddenly, you’ll want to call a professional to look at the foundation and humidity of the environment. Moreover, if the flooring on either side of the crack is uneven, you should call a professional to fix the underlying problem and level out the concrete appropriately. 

Some concrete will also crack or damage if you improperly remove flooring on top of the concrete subfloor. For example, you are removing a tile overlay from the concrete subfloor in your kitchen. You accidentally chisel directly into the concrete floor, causing a narrow crack.

If you are going to install new flooring, you will want to fix this concrete fracture to protect the integrity of the floor. If you are going to use the concrete subfloor as your new floor material, you want to fix the concrete for cosmetic and durability purposes.

So how do you start your concrete crack repair?

1. Wear safety gear.

Make sure to put on safety gear before drilling or repairing concrete. You should wear an N-95 respirator and safety goggles to protect your lungs and eyes from harmful concrete dust.

You should also use a ventilator to blow dust out of the area when working. This is especially important in garages, where trapped dust can impact the health of residents.

If you are fixing cement in an enclosed area without outside access, like a basement or warehouse, do not use a fan. This will just blow the dust around. Instead, get a partner to vacuum and collect dust in the nearby area while you’re chiseling into the concrete.

OnFloor Concrete worker wearing safety goggles and mask


2. Enlarge the crack.

You want to widen the inside of the small crack to create a “keyed” surface. This makes the base of the crack thicker than the surface, so the sealant has a greater “roots” to hold on to.

Use a cold chisel and hammer. Insert the chisel into the crack at an angle, and then hammer away at the base of the crack. Cut at least a ¼ inch deep groove inside the fracture. Break away any deteriorating concrete as well.

If you are dealing with a wide, thick crack, you won’t enlarge the inside of the crack—you’ll enlarge the entire crack. Use a circular saw with diamond blade to cut along either side of the crack. Cut a groove that is about 1/2-inch deep. This will help you completely cover the crack without worrying about future movement. 

3. Clean the area.

After chiseling and cutting, you’ll have a lot of loose concrete dust. Use a vacuum to collect the dust. This will protect workers while also ensuring dust doesn’t get trapped inside the sealant, which can cause further cracking and unleveled surfaces in the future.

You’ll then clean the area to remove any dust or debris. You can use a power washer or indoor scrubber. Be sure to dry the excess water before applying the crack filler. We recommend using a ventilator fan to speed up this process.

4. Fill with concrete.

Mix the concrete crack filler according to manufacturer instructions. We usually recommend a polymer-modified or latex-modified cement for the greatest hold. You’ll want to blend together the modifier with regular concrete mix for an adhesive, smooth texture.  

There are three key methods of filling, depending on the size of the crack.

Large cracks:

Using a trowel, fill the keyed surface with the concrete mix. Smoothen as you apply, making sure the filler is level with the surrounding floor. Fill to within 1/2 inch of the original height. Make sure to tamp the mixture firmly to remove any air pockets.

OnFloor smoothing out wet concrete with trowel

Narrow cracks:

With smaller cracks, you’ll use a bottled concrete filler. Cut the nozzle off the concrete crack sealer bottle using a utility knife. You want the opening of the bottle to be the same width as that of the crack. You can also load a concrete filler into a standard caulking gun if you feel you have more control that way.

Fill the crack with a steady hand. Move slowly to make sure the sealer moves along the line of the rack exactly. You should overfill the crack to allow for settling and shrinkage.

Hairline cracks:

For thin, shallow cracks, use a vinyl concrete patching compound. These are made of vinyl resin, sand, and cement. They work as a bonding agent on the concrete surface. You’ll apply with a tape knife and smooth with a putty knife.

5. Let set.

The concrete will start to form a skin after 20-40 minutes, but it will begin fully hardening in 1-2 hours. Later that day, you might want to wash the area with a light, citrus-based cleaner. This will remove any excess or leftover dust and sealer. Don’t use excess water, as this can impact the filler’s adhesive abilities.

Let the area set and cure for three to four days.

6. Add resurface solutions.

After the area has cured, you want to resurface the concrete. This will make sure that the concrete is uniform the surrounding area.

Add water to the resurface mix following manufacturer instructions. This will give a pancake batter consistency.

Pour the concrete resurfacing mixture on the crack. Smooth over with a rubber floor squeegee mop. Then, use a trowel to create feathered edges. This will create the most consistent appearance.

7. Stain the area.

In some cases, you may want to stain that area of the floor again. This will help match the color to create beautiful, consistent floors.  

You can usually re-stain with water-based stains, but you may not be able to with acid stains, which change the chemical makeup of the concrete.

Click to learn about how to prep concrete for staining and how to stain concrete.


OnFloor roller seal concrete


8. Seal the concrete.  

We recommend sealing the concrete again to prevent stains and renew the floor’s resistance and durability. We usually recommend a water-based polyurethane sealer. If the concrete has a rough finish, apply the sealer with a brush or broom. If it has a smooth finish, apply using a roller.

Learn more about sealing concrete for longevity here.

9. Create a maintenance plan.

If you don’t upkeep the floor, it will crack again. The more often it cracks, the deeper and more severe the fracture will get. Avoid this by properly and consistently maintaining floors. This includes frequent cleanings, annual sealing and polishing, and ongoing inspections.

Contact Onfloor now to create a maintenance plan for your concrete flooring.


The Bottom Line

Repairing concrete cracks will help preserve the look and beauty of your concrete floors for years to come. However, it’s a delicate process that requires the right materials and equipment. Drop us a line to consult about your crack one on one.

You can discuss other concrete filler options to with a professional as well:

  • Epoxy injection
  • Dowel installation
  • Polyurethane injection
  • Dry packing
  • Concrete overlays and micro-toppings

If you aren’t sure what filler is right for your concrete, contact Onfloor for a free consultation. We specialize in concrete maintenance, and we’re always ready to answer your questions.  



Previous post Next post

1 Comment