When to Worry About Cracks in Your Basement Floor

Foundations are under immense load all the time, and although concrete is a durable building material, every concrete foundation is going to crack. The important thing is being able to tell when to worry about cracks in your basement floor. In this guide, we’ll explain what to look for, what different cracks mean, and what to do about them.

Safety Note: You can try to identify the type and size of the cracks on your own, but we always recommend that you contact a foundation repair company near you to rule out potential structural and safety concerns. Many cracks can look similar in appearance, so hiring an expert for an assessment and repair is your best course of action.

Are Cracks in Your Basement Floor Serious?

You should be concerned about foundation cracks if the cracks in your basement floor are wider than 1/8 inch, spread to and up the foundation walls, appear in a circular pattern, are wet or show signs of water intrusion, have mold around them, have a white flaky substance around them, or if one side of the crack rises above the other. In all these cases, you might have structural damage or severe leaks that need a professional solution.

In all cases, the cracks need attention. You should hire a foundation repair contractor to seal hairline settling cracks to keep water and water vapor out, and more problematic cracks might need stabilization to prevent further structural damage. In the worst-case scenario, structural cracks that you don’t fix can eventually lead to major instability and even entire structure collapse.

You should be concerned about foundation cracks if the cracks in your basement floor are wider than 1/8 inch, spread to and up the foundation walls, appear in a circular pattern, are wet or show signs of water intrusion, have mold around them, have a white flaky substance around them, or if one side of the crack rises above the other. In all these cases, you might have structural damage or severe leaks that need a professional solution.

6 Causes of Cracks in Your Basement Floor

Understanding the underlying cause of foundation cracks in your basement floor is the first step in implementing a permanent fix. There are six primary reasons for cracks in your basement floor.

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 home builder pours the concrete and it dries. Shrinkage cracks can also cause wider cracking. If a crack is 1/8 inch or larger, you need to have the crack sealed to prevent water, moisture, and potentially harmful gases, like radon, from getting in.

What to Do 

Shrinkage cracks rarely indicate structural damage, so unless they’re 1/8 inch wide, they usually don’t require immediate action. You should, however, regularly inspect the cracks for changes. If the cracks get thicker or longer after a year, shrinkage may not be the only problem. 

2. Settling

Cracks from the concrete settling are the most common and will appear on virtually every basement floor and even on your basement walls. All foundations settle under the weight of your home and into the soil around them. Such cracks can also appear after tree removal near your home or if a repair requires digging to get to pipes and power and gas lines and the contractor doesn’t properly compact the soil afterward.

Settling cracks are usually thin—no more than 1/8 inch—and are easily confused with shrinkage cracks. Luckily, they usually are just as innocuous.

Unfortunately, excessive foundation settlement can occur if the soil is not properly compacted before the contractor pours the foundation. In this case, the concrete loses sufficient support from underneath, and a portion of the concrete slab will recede into the depression. This results in uneven cracks that can be a tripping hazard, cracks that continue to grow, and cracks that widen to more than 1/8 inch.

What to Do

Call a pro to inspect your basement and your home’s foundation. There may not be enough settling to warrant any repairs. If there’s too much settling, though, a pro may need to stabilize your foundation, which is not a DIY job. 

3. Heaving

Heaving is when the soil underneath your foundation expands and puts upward pressure on your basement floor, shifting a portion of the concrete upward. This is most common in areas with expansive clay soil where the ground under the floor gets wet and expands. It can also occur because of freezing soil via a process called “frost heave.” If you live in an area with above-average rainfall and expansive clay soil or cold and snowy winters, this could be an issue for you.

Unfortunately, cracks from heaving can look much like other, less serious floor cracks, like those from shrinkage and settling. More often than not, cracks from heaving will continue to lengthen and widen as the soil movement continues to stress your foundation, so monitoring cracks for growth and expansion is crucial.

If the heaving occurs in a single area—more likely with heaving from expansive soil than with freezing—you might notice that the basement floor crack forms a circular pattern.

What to Do

This issue can indicate possible structural damage, so always get a professional opinion from a foundation repair specialist ASAP. They may need to stabilize the soil underneath your home with a polymer injection, which isn't a DIY task. You may also need to hire a foundation drain installation company to implement better drainage solutions to prevent water from getting under your slab in the first place.

4. Spalling

Foundation spalling is when concrete becomes brittle and flaky, usually around a crack. Spalling occurs most often on your foundation walls, but you might notice it on your basement floor as well. Concrete is porous, so if there’s a lot of water in the soil around your home, it can wick through the concrete and evaporate into your basement. This can lead to humidity issues, mold, and pest infestation, but the changes in moisture content also cause expansion and contraction of the concrete, which weakens it.

Spalling can occur around any type of foundation crack, including those from normal settlement. While the initial damage from spalling might be minimal, it’s often a sign you have a drainage issue around your home, and water can lead to a whole host of issues for your basement.

What to Do

If you notice spalling, it’s best to have a professional address the issue immediately before it leads to structural issues. The pro may need to remove the spalled concrete and use steel to reinforce the foundation under your basement, and a foundation drainage system might be in order to prevent the problem from worsening. Again, this is not a DIY project. 

5. Leakage or Drainage 

Aside from normal settlement, water is the most likely underlying cause of foundation cracking, whether it directly or indirectly leads to cracking. When runoff soaks into the soil, it can cause it to expand and put undue pressure on your foundation, leaving cracks behind.

Water leaking into your basement is a problem for a few reasons, but if you live in a colder climate, the water seeping in through the crack could freeze and expand, widening the gap and weakening the concrete. Over time, drainage issues outside your home can cause structural damage, not to mention a whole host of other issues, like flooding, water damage, mold growth, poor indoor air quality, and more.

Some cracks that form because of drainage issues will appear wet, especially after it rains. Efflorescence is another sign that leakage might be your issue. Efflorescence is a white, flaky substance left behind on the concrete after water seeps in and evaporates. 

What to Do

You can remove the efflorescent by rinsing it with water and vinegar and scrubbing it with a stiff brush. However, you should still call a pro as soon as you notice the issue. Otherwise, you may end up with widespread water damage before you know it. 

6. Foundation Sinking

Finally, cracks can form in your basement floor if any portion of your foundation sinks into the ground more quickly than the rest. There are a few things that can cause this:

• Soil settlement from poor compaction

• Sinkholes or a karst landscape

• Rotting tree roots under your home

• Expansion and contraction of clayey soil

• Inadequate drainage around your home

• Erosion of sandy soil under or around your foundation

• Earthquakes

In most cases, cracks from foundation sinking will be uneven from side to side, with one edge higher than the other. You’ll also often see the cracks expanding out to the basement walls and potentially even climbing up the walls. Finally, you should keep an eye out for a sloping basement floor, which could indicate that it’s sinking into the ground unevenly.

What to Do

No matter how severe the issue is, foundation sinking is a cause for concern, and we recommend having a structural engineer or foundation repair specialist assess and correct the problem immediately. Do not try to make any repairs on your own.

How to Identify Basement Floor Cracks