Fixing cracks in a cement floor

Wherever they show up in the home, cracks are sure to cause a homeowner distress. The snaking jagged lines may indicate anything from peeling paint to a severe structural problem.

However, you may consider such flaws in a concrete floor to be less of a problem. Anyone who's walked on a sidewalk has seen how the material can crack over time, and this flaw might come off as more of a natural occurrence than a cause for concern. Assessing the cracks in the concrete slab of a basement or garage floor will give you an idea of why they occurred and whether they should be repaired.

Hairline cracks commonly form as part of concrete's curing process. The home improvement professional Bob Vila says the surface shrinks as the concrete dries, typically causing the cracks to show up several months after the slab was poured. EverDry Waterproofing, a company based in Toledo, Ohio, says cracks are more likely to occur as a result of major temperature changes during the curing process, and that cracks develop more easily around doors or corners.

Even larger cracks typically don't indicate a major problem, but they can lead to other issues. They can offer a way for water to seep into your basement or insects and other pests to get into your home. Vila says wider cracks—one-eighth of an inch or more—can also offer a path for radon or unpleasant soil odors to get into the home. Jeff Beneke, writing for the home design site The Spruce, says cracks can also expand over time if not remedied.

When patching a small crack, you should start by cleaning away any dirt or debris using a wire brush and vacuum. You can also chisel away the edges of the crack to allow a patch to adhere better. Apply a concrete bonding adhesive with a small paintbrush, and top it with a concrete product after allowing the adhesive to dry.

Larger cracks may require some more effort to repair. Family Handman says an effective repair is cutting around the edges of a crack with a circular saw equipped with a diamond blade, then filling the groove with new concrete and smoothing a resurfacing mixture on top.

The floor may have shrunk away from the walls as it dried, leading to cracks around the perimeter. Vila says this problem is more likely to occur in basements if the floor is not connected to the foundation wall with steel reinforcement when the concrete it poured. This issue doesn't typically indicate a structural problem, but larger cracks should still be sealed.

Cracks may also be a result of settlement of the concrete slab, especially if the soil underneath was not properly compacted. EveryDry Waterproofing says homes are typically designed to account for some soil movement, but that more pronounced settling can lead to noticeable signs such as gaps between the floor and walls or the walls and ceiling, walls pulling away from each other, or cracks on the walls.

Depending on how severe the settlement is, parts of the slab may be forced upward and create a tripping hazard. Vila says filling the lower area with a self-leveling cement can remedy this issue.

More severe problems can occur with major soil movement beneath the slab. For example, soil with clay will expand when it gets wet, potentially putting enough pressure on the concrete to crack it and push a chunk of the slab upward. EveryDry Waterproofing says your concrete may also shift as a result of frost heaves during colder weather.

More pronounced cracking caused by moisture issues is best resolved by a professional, since it requires steps such as replacing the floor or installing a drain. You should also look for related signs that the cracks may be related to foundation issues, such as noticeably sloping floors or difficulty in opening doors or windows.

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