Cracks in basement floors can make any homeowner nervous. You might worry about structural issues, water seepage, or foundation issues. While some cracks in the concrete slab are harmless, others can point to bigger concerns. Understanding what causes them can help you decide whether to take action or simply keep an eye on things. Let’s look at the most common reasons concrete basement floors crack and what you should do about them.
1. Natural Settling and Shrinkage
Concrete flooring naturally expands and contracts as it cures, which can lead to small cracks.
When a house is built, the concrete in the basement slab goes through a curing process. As it dries, it shrinks slightly, which can create hairline cracks. These are normal, non-structural settlement cracks and don’t mean there’s a serious problem. Over time, as the ground beneath your home settles, small shifts can also cause minor cracks to form. Most of these concrete cracks don’t require any repairs unless they start to widen or you see signs of water intrusion.
Signs That a Crack Is Just from Shrinkage:
- Thin, hairline cracks that don’t spread over time
- No change in height between the two sides of the crack
- No water seepage coming through the crack
If the cracks stay the same size, don't create an uneven surface, and remain dry, they’re usually nothing to worry about.
2. Moisture and Water Pressure
Too much moisture content in the soil can put pressure on your basement floor slab, leading to cracks.
Water naturally moves through the ground, and when it builds up around your foundation, it creates hydrostatic pressure. This upward pressure pushes against the concrete, and if it becomes too much, the floor slab may crack. Heavy rains, improper drainage, or high groundwater levels can make this worse. If you notice cracks in concrete that are allowing water intrusion, it’s a sign that excess moisture is affecting your basement concrete.
To help prevent this:
- Keep gutters clean and downspouts clear so water drains away from your home
- Make sure the ground around your house slopes away from the foundation walls
- Check for plumbing leaks that could be adding excessive moisture
If cracks are letting water in, sealing them and making sure you have proper drainage around your home can help prevent larger issues and water damage.
3. Soil Movement and Foundation Shifts
Changes in the soil beneath your home can cause cracks in your basement floor.
Different types of soil react to moisture in different ways. Some expand when wet and shrink when dry, which can cause movement under your foundation. This shifting can create stress on the concrete floor, leading to cracks. Tree roots, heavy construction nearby, soil erosion, or normal settlement can also play a role.
Cracks caused by soil movement or poor soil conditions are often wider than hairline cracks and may have uneven edges. If you notice new cracks forming or existing ones getting bigger, it may be worth having a professional do a foundation inspection for structural damage or underlying issues.
FAQ
Can basement floor cracks let radon gas into my home?
Yes, cracks in your basement floor can allow radon gas to enter. Radon is a naturally occurring gas that can be harmful in high levels. If you have cracks, especially ones that go deep into the foundation, consider sealing them, testing your home for radon, and getting a radon detector.
Should I fill basement floor cracks myself or call a professional?
It depends on the size and severity of the cracks in the concrete surface. Small, hairline cracks can usually be filled with concrete sealant from a hardware store. If you have cracks with heaving, getting wider, deeper, or growing over time, it’s best to have a professional assess the situation to make sure there aren’t underlying structural issues.
