You may not be able to stop cracks in their tracks, but at least you can identify them
Hairline cracks under 1/8 inch wide and level across the gap are natural and aren’t usually cause for concern.
Cracks that continue to lengthen or widen after your foundation has settled are a sign of an issue.
Any crack that leaks should be cause for concern and needs sealing.
Professional repair is always the best course of action for cracks.
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.
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.
Hairline cracks under 1/18 inches are normal, but if you spot larger or deeper cracks, call a pro immediately. Cracks exceeding 1/4 inches are a sign of more serious structural damage and should be handled by a foundation pro.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
Basement floor cracks can occur for a variety of reasons, and being able to identify the different issues is crucial. Just telling the difference between a normal settling crack and a sinking crack and hiring the appropriate repair specialists could save you time and money, especially if you catch an issue before it gets severe. Below are some specific things you can look for to help you identify major issues in a timely manner.
Look for water seepage: Any visibly wet areas or efflorescence around the crack, especially after it rains, can help you identify if soil moisture is an underlying cause.
Look for mold growth: Mold growth suggests moisture, so the presence of mold near a crack could help you determine if soil drainage is the issue. At the very least, it can help determine if you need to seal your foundation cracks.
Check for wall cracks: If basement floor cracks extend up the walls, you’re likely dealing with a sinking foundation, which demands immediate attention from a pro.
Look for uneven cracks: Cracks where the floor on one side is higher than the other could indicate foundation sinking or heaving, both of which are severe.
Look for growing cracks: All basement floors crack during settlement, but if cracks continue to lengthen or widen a year or so after construction, you probably have a more serious issue.
Assess for pest infestation: If you have a pest infestation in your basement, it’s likely because the cracks on your floor were either caused by leaking or are leading to leaks. In either case, you’ll need to have them sealed.
Look for wide cracks: Any basement floor crack over 1/8 inch wide needs sealing, but we also recommend having a repair company look at it. Wide cracks are more often a sign of foundation damage from unexpected soil movement rather than natural settling.
There are a few different types of foundation floor cracks you can be on the lookout for when carrying out your own foundation inspections.
Hairline cracks are less than 1/8 inch wide and usually appear because of normal settlement. Provided they don’t continue to grow, sealing them to prevent water and moisture intrusion is often an adequate solution.
Cracks that get to 1/8 inch wide or more are more likely to be structural in nature and may require stabilization and sealing. Always have a professional inspect these cracks to determine the underlying cause and appropriate solution.
Cracks with one edge pushing over the other often form because of foundation sinking. These are severe and require immediate professional attention.
Cracks that form a circle on the floor are usually from soil heaving. You should have these addressed by a professional and then sealed.
Basement floor cracks that spread to the wall and then travel up it are usually signs of structural issues and foundation sinking.
In some cases, it’s possible to carry out a DIY solution to the cracks in basement floors, but you should take great care to identify the underlying cause of the issue before you do so. Some types of basement floor cracks can indicate severe structural damage, so if you’re ever in doubt, we strongly recommend hiring a professional to carry out an assessment and repair.
If you find hairline cracks in your basement floor and confirm over time that they aren’t lengthening or widening, you can seal them yourself using an epoxy or concrete crack sealant. This will help keep water and radon out of your basement, although you should also invest in a radon detector to ensure the leakage is properly addressed.
If there is any sign of moisture intrusion, mold growth, unevenness across the crack, or signs that anything other than normal foundation settlement could be the cause of the cracking, call a professional right away. DIY solutions might seem appealing because of the lower costs, but you could end up with a potentially dangerous problem if you go too long without a proper professional repair.
Yes, water and water vapor can seep through cracks in your basement floor, which means you should address all basement floor cracks, even if they don’t indicate structural issues. Sealing settling cracks and shrinkage cracks is a good idea to keep water and moisture outside where it belongs. Doing so can improve your indoor air quality, reduce the risk of mold growth, make your home more comfortable, and help prevent pest infestation.
Yes, all basement floors crack in response to the natural settlement of the soil around them and from concrete shrinkage as it cures, and you’ll see hairline cracks as a result. However, you should keep an eye on your basement floor to see if cracks continue to lengthen or widen or show signs of water intrusion. In any of these cases, the problem is likely not settling or shrinkage, and a professional repair is necessary.
The best solution to fix a foundation crack in your basement floor depends on the underlying cause. If you just have hairline cracks from settlements that are no longer growing, the best option is to seal them with a crack sealant. If the cracks continue to grow, one edge rises above the other, or there are signs that water is getting in through the crack, a professional repair will be necessary. Depending on the root cause, your professional may employ foundation underpinning or some other type of stabilization, seal the cracks, or install a drainage system.
