Proper curing of the concrete is also crucial to help prevent early age cracking. Curing is the act of helping maintain concrete moisture by preventing its rapid loss. If the concrete loses moisture from its surface too quickly it will shrink (faster than the concrete below the surface) causing a condition referred to as map cracking.
Wide cracks in concrete are best patched and sealed with a concrete patching compound. Smaller cracks, less than 1/4 inch wide, can be repaired with a concrete caulk or liquid filler. Patching compounds typically are mixed with water and applied with a trowel. They have a texture similar to grout and can be smoothed and textured to blend with the surrounding area. However, the color of the patch will look like new concrete and will not match the old concrete. Hiding the patch completely requires painting the surface with an appropriate concrete paint.
How to Repair Wide Concrete Cracks
The secret to fixing wide concrete cracks is to undercut the sides of the crack to give it an inverted 'V' shape. This helps the repair material to 'key' into the crack, creating a mechanical bond in addition to the chemical bond between the patch material and the concrete.
- Chisel the crack with a hammer and masonry chisel to widen the base of the crack and to dislodge any loose material from the old concrete.
- Remove all debris from the crack, using a wire brush. If desired, clean the crack with a pressure washer or a garden hose and spray nozzle.
- Remove all water and debris from the crack with a wet/dry shop vacuum or a brush. Work carefully to remove all dust and grit from the crack. It's OK if the surfaces are wet, but there should be no pools of water.
- Mix the concrete patching compound, following the manufacturer's directions.
- Trowel the compound into the crack. Stab the trowel into the compound to remove air pockets and help work the patching material deep into the crack. Fill the crack up to the surrounding concrete surface.
- Smooth the surface of the patch with the trowel, feathering the compound into the surrounding concrete.
- Brush the surface of the patching compound with a dry paintbrush to texture the surface, if desired.
- Let the compound cure as directed.
- Paint or seal the surface of the patch and surrounding area, if desired.
How to Repair Narrow Concrete Cracks
Narrow concrete cracks can be filled using masonry crack elastomeric filler that can be applied with a caulking gun. Alternatively, many products come in bottles with an applicator tip. Very small cracks, such as hairline cracks, can be repaired using a vinyl concrete patching compound applied over the crack and then smoothed with a putty knife or trowel. For hairline cracks, applying repair caulk or crack filler over the cracks usually is not effective, as the caulk tends to peel off of the surface over time.
Narrow cracks can be deep, often extending through the entire thickness of the concrete slab. Therefore, it's a good idea to start the repair by stuffing foam backer rod into the crack to create a base to hold the repair material. Backer rod is solid in a variety of sizes; use a rod diameter that is slightly larger than the width of the crack. Stuff the backer rod into the crack with a screwdriver to a depth of 1/4 inch. Fill the crack with the repair material, following the manufacturer's directions.
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A driveway must be poured correctly in order to be crack-free. (Photo by Summer Galyan)
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Over time, your concrete is susceptible to cracking. Here's what you can do to prevent it and protect the look of your sidewalk or driveway.
It's very common for concrete to develop cracks, scaling, crazing and pitting. All concrete has the tendency to crack, and it's not possible to produce completely crack-free concrete.
Concrete expands and shrinks with changes in moisture and temperature. The overall tendency is to shrink, and this can cause cracking at an early age of the concrete. Irregular cracks are unsightly and difficult to maintain but generally don't affect the integrity of concrete.
Control joints in concrete driveways or slabs are simply pre-planned cracks. Control joints create a weak place, so that when concrete shrinks, it will crack in the control joint instead of randomly across the slab.
The American Concrete Institute addresses this issue: “Even with the best floor designs and proper construction, it is unrealistic to expect crack-free and curl-free floors. Consequently, every owner should be advised by both the designer and contractor that it is normal to expect some amount of cracking and curling on every project, and that such an occurrence does not necessarily reflect adversely on either the adequacy of the floor’s design or the quality of its construction.”
The most popular explanation for the concrete cracking is the freeze-thaw cycle in the winter.
It's recommended to use sand on all concrete instead of salt. Salt will facilitate the freeze and thaw cycles that will then create the problem with pitting and cracking. When the temperature reaches 18 degrees, the concrete will freeze. At 35 degrees, it will melt and cause the cracking, pitting, crazing and scaling.
Concrete also cracks in the extreme sun, as it heats the concrete and causes it to expand. At the end of the day, the concrete contracts and regresses to its original, unbaked position.
A homeowner can help prevent cracking, scaling, crazing and pitting by yearly applying a good acrylic silicone solvent-based sealer to their concrete. A concrete contractor can also repair cracks with an epoxy injection, dry packing or routing and sealing techniques to stabilize the cracks.
Editor's note: This is an updated version of an article originally published on Aug. 5, 2011.
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Mr. Concrete of Indiana, Inc. has provided specialized concrete, aggregates and related solutions to the communities of Indiana in both residential and business environments for more than 35 years.
How Do You Keep Concrete From Cracking
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