3 Reasons There Are Cracks in Your Basement Floor, and When You Should Be Concerned

Meg Scanlon
Written by Meg Scanlon
Updated September 21, 2021
Woman standing on a cracked floor
Pras Boonwong/EyeEm via Getty Images

Your basement floor cracks may simply be a superficial issue, but have a professional check out the situation for peace of mind

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Seeing cracks in your concrete basement floor can be unsettling, but there are lots of possible reasons why—and not all are cause for alarm. Here are some clues as to what's causing that unsightly crack, and whether it can be a telltale sign of larger foundational issues.

A Note on Safety: You can try to identify the type and size of the cracks on your own, but always consult with a local foundation professional to rule out potential structural and safety concerns. Many cracks can look similar in appearance, so an expert can assess the situation properly.  

1. Shrinkage

Hairline cracks can appear as thin, fine cracks in concrete flooring. They can be jagged, web-like, or straight, and are often a result of shrinkage. 

Shrinkage occurs when the concrete mix dries and pulls apart. This is a natural part of the concrete curing process and can appear between two and 12 months after the concrete is poured and dried. Shrinkage cracks can also cause wider cracks, if a crack is one-eighth-inch or larger, it needs to be sealed.

Sealing prevents water, moisture, and soil gases like radon from entering your home. Radon is a carcinogen that can cause cancer, and it’s difficult to detect. Have a local professional test for radon to give you peace of mind, and you can also install a radon detector in your basement.

2. Settling

If soil is not properly compacted before the cement is poured, it can settle over time and cause cracks. Such cracks can also appear after a big tree is removed near your home, or if a repair requires digging to get to pipes and power and gas lines and the soil is not compacted afterward. 

The portion of the concrete slab that has less support underneath it will recede into the depression. This results in uneven cracks that can be a tripping hazard. 

This problem is more significant and complex to fix than shrinkage cracks and is best left to the professionals to assess the situation. Settling can cause safety concerns including potential foundational problems. The sooner you address this problem the better, as it can cause more issues over time, and more money in repairs. 

3. Heaving

Heaving is when the soil underneath your foundation absorbs moisture and expands, shifting the floor upward. This often happens because of humid or freezing soil, so if you live in an area with hot and humid summers and cold and snowy winters, this could be an issue for you. This problem is also more common in areas with clay soil. 

Heaving is often identified as cracks in the floor near any basement support columns and pillars; you may even see some cracks appear on the wall near the floor. This issue can indicate possible foundational problems, so always get a professional opinion from a foundation repair specialist ASAP.

Look For Water Seepage

Water seepage on the floor
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An easy way to find cracks is by looking for water seepage. While water itself generally does not cause the cracks, the cracks can be an avenue for water to come in because the soil below the foundation is very moist. 

Water seepage can lead to mold, causing allergies and respiratory symptoms. Black mold can also appear and cause symptoms such as coughing, sneezing, and eye irritation. 

If you see mold in your basement that is black or dark green and shiny in appearance, then you may need to have a mold removal expert near you take a look. Only a pro can identify mold conclusively. 

While the cracks may be superficial and merely an eyesore, due to several potential safety concerns, it is always recommended to have an expert assess the situation.

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