How to Fix Cracks in a Concrete Patio

Concrete Cracks

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Cracks in a concrete patio are unsightly. But that's only the start of it. Cracks invite weed growth and they collect debris. Shifting soil and freeze-thaw events can turn small cracks into wider and longer cracks, eventually leading to the need to demolish and rebuild your patio.

Non-structural cracks in concrete can be repaired quickly with simple methods and inexpensive materials. This fix effectively blocks weeds, cures the debris problem, and prevents further damage to the patio for years.

Tools and Supplies You Will Need

  • Polymer-based concrete crack filler
  • Solid crack filler: closed-cell backer rod or clean sand and funnel
  • Caulking gun
  • Hammer
  • Heavy-duty flat mason's chisel
  • Wire brush
  • Shop vacuum
  • Safety glasses
  • Hearing protection
  • Putty knife
  • Utility knife

Instructions

Concrete cracks cannot be patched with concrete since concrete contains aggregate rock pieces that are too large to fit in cracks. Instead, for cracks up to 1/2-inch wide and 1/4-inch deep, you should use a polymer-based (sanded acrylic-latex) filler that you inject into the crack with a caulking gun and smooth over with a putty knife. Such elastomeric fillers have the benefit of allowing the concrete to slightly shift over time while maintaining structural stability.

While the patch will always be noticeable to some degree, you can minimize its visual impact by choosing a filler that closely matches the color of your patio. After the repair, surfacing the entire concrete patio or painting it are two options for completely hiding the crack repair. If you intend to do this, just make sure that you choose a paintable crack filler.

Wait for the Right Conditions

Unlike the controlled environment of a home's interior, concrete patios are subject to temperature and moisture fluctuations that can severely hamper your repair. For most patch materials, both the air and the concrete must be between 50 F and 90 F. The concrete should be perfectly dry and no precipitation should be forecast for the next 24 hours.

Widen the Crack

Widening the crack and creating a V-shape will help the patch materials stick better over the long-term. Wearing safety glasses and hearing protection, place the edge of the masonry chisel into the crack. By keeping the chisel at a 45-degree angle, the chisel will help you form a V-shape. Tap the back of the chisel lightly with the hammer to force it about 1/4-inch into the crack. Continue to follow the crack as you tap, being careful not to chip out large sections of concrete. Try to maintain a width-to-depth ratio of 2:1 at all times.

Brush Out the Crack

With the wire brush, vigorously brush the crack in order to dislodge any remaining small particles. Brush in the direction of the crack.

Clean Out the Concrete Crack

With the shop vacuum, thoroughly clean out the concrete crack. Remove concrete particles, since any left behind can compromise your repair.

Add Solid Crack Filler (Optional)

Assess the depth of the crack. If the crack is partially or completely deeper than 1/4-inch, fill in the necessary sections to bring it up to that height. It is not desirable to use the liquid crack filler for deep areas as this extends curing time, can result in sinking filler, and adds to the overall cost of the project.

One way to add solid filler is to dispense clean sand by hand through a funnel. One hand holds the funnel, while the other hand holds a small amount of sand and slowly drops it into the funnel. This method has the advantage of being very inexpensive and allowing you to vary the height of the crack filler as you go.

Another option is to force closed-cell backer rod into the crack. Three-quarter-inch backer rod is designed to fit into 1/2-inch cracks. Force the backer rod into the crack as much as you can with your fingers. Cut off the backer rod when you reach higher areas that do not need filler. If you reach sections where it is difficult to press the rod with your fingers, use a blunt tool such as a paint stirring stick, since sharper tools like screwdrivers may pierce the rod. Make sure that the backer rod is firmly in place before proceeding to the next step.

Add the Concrete Crack Filler

Cut off the end of the applicator tip. Shake the crack filler container if necessary. Some crack fillers will separate, so squirt a small amount of filler onto a piece of cardboard until thicker filler emerges. Force a bead of the filler into the crack, slowly drawing it along and making sure that the filler fully settles into the crack before moving on.

Trowel Down the Filler

If there are areas that completely fill the crack from side to side and are flat, they will not need additional tooling. For high areas, draw the putty knife in the direction of the crack to flatten the filler. For areas that appear low or have pockets, add more filler in those areas and then immediately trowel down with the putty knife.

Allow the Patch to Cure

Let the patch material cure for over 24 hours before use or before painting or surfacing.

Preventing Damage Over the Winter

Winter is harsh on all exterior materials, including concrete patios. Whether your patio is cracked and in need of repair or has already been repaired, take these measures to make sure that winter elements do not damage your patio.

  • Make sure that all cracks are sealed or remain sealed since freeze-thaw events can easily widen cracks.
  • Ice melt, or de-icers, can potentially harm concrete. Unless you expect to be walking through the patio and safety is a concern, the best option for the concrete may be to let the snow and ice melt naturally.
  • Snow shovels with metal wear-strips can damage concrete. Sweep the concrete with a push-broom or purchase a snow shovel that has no metal that will come into contact with the concrete.
  • Spalled concrete that flakes off in thin horizontal pieces should be patched immediately. Much like peeling paint, spalling concrete tends to introduce moisture and lead to more spalling. A concrete resurfacer that pours on and spreads out with a squeegee, trowel, or broom is the best way to repair these large, shallow areas.
  • Consider covering your patio. Solid roofing or canopies that prevent moisture from gathering on the patio not only minimize damage to the concrete, but they also help you enjoy your patio in the off-season.
  • Do not build or install a firepit that comes into direct contact with the concrete patio. If the firepit is at ground level, do not place it on the patio. If the firepit is elevated, make sure that the elevation is sufficient to prevent thermal damage to the concrete.