There are at least three good reasons for the prompt repair of cracks in concrete:
1) cosmetic
2) eliminating a hazard
3) preventing further damage
Most home concrete cracks are found in drive-ways, garage or carport slabs, walks and paths, patios, and sometimes even in the foundation or slab that supports the home.
Frequently severe cracks in concrete are the result of a soil condition that needs attention. For example, there may be an inordinate amount of water in the soil beside or below a path or foundation causing the soil to expand and hence the concrete to crack. All of the cosmetic crack repairs in the world will do nothing to correct a drainage problem that conceivably could result in severe damage if left uncorrected.
Excessive moisture due to overwatering or poor drainage should be addressed prior to making any crack repairs. Foundations or structural slabs with excessive cracking or with cracks that are larger than 1/4" in width should be examined by a structural or civil engineer to access the damage. If the damage is severe a geotechnical or "soils" engineer should be consulted. Even in the best of conditions, concrete will move a fraction of an inch here or there, not always resulting in a crack. Concrete expands and contracts with the temperature, expanding on hot days and shrinking when the weather is cold.
Therefore, when patching cracks in concrete we suggest that you use a product that will give a little here or there. Elasticity is important. The more elastic the product the less likely the crack will reappear.
Just as with painting, the key to successful crack repair lies in the preliminary steps taken. To begin, the crack should be clean and free of any loose chips. A light going over with a wire brush will remove any flaking. Small cracks, 1/8" or less, should be opened up slightly with a flat-bladed screwdriver or the sharp end of a bottle opener. A light wire brushing followed by a rinsing with the garden hose will complete the preparation.
Our favorite patching product for most cracks, vertical or horizontal, is a vinyl concrete patch. It is usually packaged dry in a box and mixed with water. We like to use latex in place of the water to give the product some added elasticity and adhesion. Latex additives like the patching compounds can be found at most hardware stores or home improvement centers.
Mix the concrete patch to the consistency of a thin paste and trowel it into the crack with a two-to-three-inch putty knife. Scrape away any excess to create a smooth finish. Mix only a small amount at a time since most products dry quickly. Tools and buckets should also be cleaned immediately for this reason.
Large gaps (1/4" or greater) in concrete where a path or patio joins a foundation or where joints between concrete pads have opened up require a slightly different patching method. Here, we suggest that you use a siliconized latex concrete caulk. This product is pumped into the joint with a caulking gun and due to the silicone will remain pliable to allow for expansion and contraction. Because most of these caulking products are self-leveling no additional work is required. Large gaps may require more than one application.
The price of a small box of concrete patch and a tube of concrete caulk, each under $5.00, along with a small investment of your time, will improve your home's overall appearance, make it safer and less likely to incur future problems.
