Basement Floor Cracks: Causes and How To Repair

Even for those not afraid of the dark, venturing into the basement can be a hair-raising experience for those who discover cracks spidering along the basement floor. The good news is, most of the time these cracks are no cause for concern as they’re often caused by the home going through its natural settling process or the concrete foundation slowly drying.

While these cracks don’t present structural issues, those larger than a hairline still offer a place for pests, moisture, and even dangerous gases from soil to enter the home, making it imperative that you seal these cracks.

In this article, we’ll discuss what causes those basement cracks, why you should be concerned about them, how to repair basement floor cracks, and when it’s time to call in the pros.

Cracks in basement floor

What Causes Basement Floor Cracks?

A wide variety of factors can cause the floors in a basement to crack. Cracks can indicate everything from normal wear and tear in an older home to poor drainage around the foundation of a newer home to structural damage. In this section, we’ll review all the causes of basement floor cracks.

Wear and Tear

Some cracks simply happen due to the normal settling process of the house over time, the natural drying out process of concrete, or the natural changes in soil temperature and water content around the foundation, as we’ll discuss in more detail below.

This normal wear and tear will create small hairline cracks that, though aesthetically unappealing, aren’t an indication of structural problems.

Although wear and tear isn’t an indication of structural problems, it can be a place for pests to enter the home if the cracks are wider than 1/16 of an inch, in which case it’s wide to fill them.

Poor drainage around the foundation

Improper drainage around the foundation that causes water to flow towards instead of away from the foundation can cause water to build up around the foundation and even under the basement floor, creating hydrostatic pressure that pushes on the foundation, causing cracks to appear in the basement floor.

If this is the cause of the cracks in your floor, it’s imperative that you fix the drainage problem before embarking on a crack repairing effort by grading around the foundation to ensure water is directed away from home.

You should also check the gutters and downspouts to make sure they are directing water away from the foundation and not toward the foundation.


When basement floor cracks also show heaving, this is a sign of a large problem with the foundation. Heaving occurs when the floor not only cracks but a section pushes upward, causing the two sides of the crack to be misaligned.

When this takes place, it can mean several things. In some cases, it can be caused by the soil beneath the foundation creating upward pressure that lifts the concrete floor and cracks it.

Heaving can also be caused by tree roots growing under the home, creating pressure. When heaving occurs, it’s best to call the professionals as the foundation will need a more comprehensive (and costly) repair than what a concrete patch offers.


Concrete consists of a mix of water and concrete. As such, as the water evaporates, the concrete slowly shrinks. The temperature in the basement largely impacts this drying process.

In newer basements, high temperatures can cause the concrete to cure too quickly and crack. Similarly, if the temperature drops too low, this can cause the moisture in the concrete to freeze, creating cracks.

Shrinkage is more likely to impact places where the concrete is hemmed in, such as in corners or around doorways. Even after concrete cures, it will slowly shrink over time, which can lead to cracks.

Fortunately, shrinkage rarely leads to cracks that cause structural damage. However, they can serve as access points for pests, so it’s important to seal them when they appear.


Settlement happens when the ground soil beneath the foundation shifts under the weight of the home. Most homes can handle about an inch of soil movement. Tree roots and poor drainage in the basement can also cause settlement to happen. When this shift occurs, it can cause the foundation to crack.

One way of determining if settlement is causing the cracks is to look at other parts of the home. Settlement can cause the floor to pull slightly away from the walls or cause small gaps to appear between the ceiling and walls.

Cracks on the walls are also a common sign of settlement. More serious signs include doors and windows that won’t open or close properly and walls or floors with a noticeable slope.

Frozen Soil

Freezing soil, referred to as frost heave, can also be a source of cracks in the basement. During colder months, as the soil freezes, thaws and refreezes, it causes the soil under and around a home to expand and contract, causing a shift that creates cracks in the floor.

These cracks typically form around the support columns in the floor and most often occur with silty soil types with a high water capacity.

If you notice these types of cracks, there are few ways to prevent frost heave. One option is to replace the soil around the foundation with gravel or fill sand. Installing a drainage system around the foundation or insulating the foundation and ground around it are also options.

Also, make sure the gutters around the home and corresponding downspouts are channeling water that could saturate the soil around the foundation and cause problems when it freezes.

What Do Cracks In Basement Floor Mean?

One of the best ways to determine what’s causing the cracks in the basement floor is to analyze their shape, size, and location. In this section, we’ll cover the most common crack types and what they can tell you about what’s going on with your basement floor.

Hairline Cracks

Hairline crack in basement floor

If you’re going to have cracks in your basement floor, then these are the type that you want. Hairline cracks are typically caused by shrinkage in the floor over time as the concrete dries and pulls the concrete slightly apart.

A basement floor can take up to a year to fully dry and cure, so expect these cracks to appear in newer homes.

Often, hairline cracks require no repair as they’re too small to cause seepage or allow pests to enter the home. However, if you find them to be unsightly, you can repair them with cement sealant or patch.

Keep in mind that patching hairline cracks isn’t a great option for aesthetic repairs as the repair cement will be much more visible than the hairline crack. If you are concerned about aesthetics, you’ll need to repair the cracks then paint the floor.

Cracks Between 1/16” and 1/8”

Crack in basement floor

If you have larger cracks, fear not. Large cracks up to 1/8 of an inch wide are usually not the signs of bigger foundation problems but, like hairline cracks, also the result of shrinkage in the cement.

That said, these larger cracks should not be left alone. A 1/8-inch crack can allow seepage to enter the basement or even gases from the soil below, including the dangerous gas radon. They are also a potential place for insects to enter the home.

As such, these wider cracks should be sealed.

Larger Than 1/8-Inch

Basement floor cracks

While even cracks that are larger than 1/8 of an inch may simply be the result of drying and settling, when a basement floor crack is also combined with heaving, it can be a problem.

Heaving is when a section of the floor is pushing up and away from the floor due to the expansion of the soil below. This usually occurs with expanding clay soil, which pushes the concrete slab of the foundation upward, creating the crack.

As we discussed above, heaving is not a problem that can merely be patched. The underlying problem needs to be addressed, which requires a foundation repair professional.

Between Basement Wall and Floor

Crack Between Basement Wall and Floor

While a growing crack between the basement wall and floor can be a sign that the house is settling, causing the foundation to sink lower than the wall, it often isn’t.

There is supposed to be a small gap between the walls and the floor called a cove joint and should never be sealed. Sealing the cover joint to prevent water from entering will simply force moisture to find another way to enter, creating hydrostatic pressure on other parts of the foundation, causing cracks.

The pressure can also cause the water to overwhelm the sealant, rendering all the hard work you put into sealing the cover joint useless.

A better option is to prevent leaking in the basement by using solutions such as improving the drainage around the foundation or inside the basement.

Is Crack in Basement Floor a Problem?

Determining whether that crack in the basement floor is a problem largely depends on the type of crack. While most hairline cracks won’t be an issue, anything larger than 1/16th of an inch should be repaired or could lead to the following problems.

Water Leaks

Water wants to enter your basement and cracks in the basement floor are one means of doing so. The foundation creates pressure on the soil below, which squeezes the soil like a sponge, sending the moisture up through the crack. The only way to prevent this from happening is by sealing the cracks.


While most people will fix a crack in the wall, they often pay little attention to the cracks in the basement floor. Insects live in the soil around your home, so a crack in the floor that opens into that soil is a clear path for insects to gain access to the basement. The only way to keep them from doing so is to seal those cracks.

Structural Damage

As we’ve already discussed, hairline cracks are usually not an indication of structural problems with the home but rather the result of the natural drying process of the concrete that makes up the foundation.

However, larger cracks, especially those that demonstrate heaving, can signify structural damage. In these cases, it’s imperative that a professional inspect the cracks, so you can take action to prevent further damage.

Heaving cracks may require large sections of the entire foundation to be removed so the problem below can be addressed.


While some see the basement as a utility space in the house and don’t mind a few hairline cracks, you may find them to be an unsightly blemish on your beloved home that irks you every time you go to the basement.

While your desire for a smooth basement floor may be a motivator for repairing those cracks, keep in mind that repairing a hairline crack won’t solve your aesthetics issue and will likely make it worse.

Basement floor crack repair products will not create an invisible patch on the floor but will instead highlight the cracks by leaving a wider line of concrete that doesn’t perfectly match the color of the floor.

If aesthetics are a major concern, you’ll need to paint over the cracks after repairing them, so make sure to select a paintable patch or sealant.

How to Fix a Cracked Basement Floor?

Sikaflex Crack Flex Sealant, Gray, High performance, textured polyurethane sealant, self-leveling, sealant for sealing horizontal cracks, 10,1 fl. Oz

Once you’ve diagnosed the problem, it’s time to repair the basement floor crack.

Step 1: Find out what the cause is

Use the above descriptions to determine what has caused these cracks. In most cases, it is something natural, like the home settling. However, if it’s heaving, you’ll need to stop here and call in the pros.

Step 2: Remove Loose Pieces

Cracked floor

Start by getting rid of larger pieces of debris by removing them with your fingers or using a wire brush to get the piece out. A shop vac is often the best way to clear loose material from the crack.

Step 3: Taper the Crack

Now that the crack is free of dirt and debris, you’ll need to create a wide enough surface for the concrete sealant to penetrate the crack and fill the hole.

There are a couple of ways to do this. You can accomplish this task by hand using a hammer and chisel to create a V-shaped opening that runs along the crack.

A faster method is to use an angle grinder to widen the opening of the crack. Make sure to use a respirator when tapering the crack, especially if using an angle grinder, as it will release a significant amount of concrete dust into the air.

Step 4: Clear the Cracks of Any Debris or Dirt

Chiseling or grinding out the crack will create a considerable amount of dirt and debris that must be removed before you can apply the patch. Use a brush to remove debris from the crack and then apply a shop vac to eliminate any loose material.

Be sure to get everything, as any debris left in the crack will prevent the concrete repair from properly adhering.

Step 5: Apply Bonding Adhesive

Brush bonding adhesive onto the crack and let it thoroughly dry. You may be tempted to skip this step and begin applying the concrete patch. This would be a mistake.

Bonding adhesive is necessary to ensure the patch adheres to the existing concrete. If you fail to apply the bonding adhesive and the patch pulls away from the concrete, you’ll have to grind out the patch and complete the repair all over again.

Step 6: Apply Concrete Patch

You’ll need to apply the concrete patch in layers to ensure a patch that penetrates deep into the crack, making it thick enough to resist any hydrostatic pressure from moisture in the soil below.

The goal of the first layer is to create a deep base for the repair. Use a scraper or putty knife to push the concrete patch into the crack as much as you can. This first layer should be below the level of the floor. Use a stick to push the concrete down into the crack.

Allow the patch to harden (check the instructions on the product packaging for dry times) then apply the second layer, pushing it down to meet the first. Use a trowel to bring the second layer level with the basement floor.

Step 7: Let it Dry

How to fix cracks in basement floor

Allow the patch to dry before subjecting it to foot traffic, water, or paint. Most concrete patches cure in about three days but check the packaging for specific dry times. Remember, allowing the patch to dry properly is integral to it reaching its maximum strength.

Concrete Patch Products

Rust-Oleum Wall-Surface-Repair Products

Rust-Oleum 301012 Concrete Patch & Repair, 24 oz, GrayFast drying and easy to mix and use, this concrete patch from Rust-Oleum is one of the best options for fixing a concrete floor. It consists of a two-part epoxy that you mix just before applying the patch.

The patch is stronger than concrete and doesn’t shrink, which means you don’t have to worry about chipping or crumbling. It will fill cracks up to 1/2-inch deep, making it ideal for minor to moderate basement cracks.

This product also produces low VOCs, ideal for basements with little to no ventilation, and is ready for paint in just 8 hours.

DAP Self-Leveling Concrete Sealant

No products found.No products found. is one of the easiest options on the market. It requires no mixing or tools for application. Simply put the tube in a caulk gun and apply the sealant to the cracks. It dries quickly, making it impervious to water in just three hours.

The sealant also self-levels, so there’s no need to worry about using a trowel to level the sealant with the floor. DAP will cover cracks up to 1/2-inch wide.

Unlike other concrete sealants that harden, DAP remains flexible, allowing it to expand and contract with the floor without cracking. DAP is also paintable, making it a good choice for those looking to finish the floor once the repair is complete.

SIKA Sikaflex Crack Flex Sealant

Sikaflex Crack Flex Sealant, Gray, High performance, textured polyurethane sealant, self-leveling, sealant for sealing horizontal cracks, 10,1 fl. OzLike some of the other sealants that work with a caulk gun, Sikaflex Crack Flex Sealant doesn’t harden but rather dries to a flexible elastic consistency that allows it to flex, expand and contract with the concrete floor, ensuring it won’t crack or chip.

It’s easy to apply; simply squeeze the sealant into the crack, then allow it to self-level with the floor. There’s no trowel required to level the sealant with the surface of the basement floor. SIKA sealant, which dries to the touch in just a couple of hours, can fill cracks up to an inch wide and is paintable.

Damtite Concrete Super Patch Repair

Damtite 04072 Concrete Super Patch Repair, 7 lb. PailDamtite Concrete Super Patch Repair is a great option for fixing large cracks with its ability to fill gaps up to 3 inches when applied in multiple layers. It comes in two containers, one that includes a liquid and the other a powder.

Simply add the liquid to the powder, mix and apply. Use a trowel to push the patch into the crack, then level with the surrounding floor. Damtite comes in a 7-pound pail, making it ideal for repairing larger cracks. Damtite sets in 4 hours and cures in two days, after which it is paintable.

Two-Part Epoxy Adhesive Paste

PC Products 72561 PC-Concrete Two-Part Epoxy Adhesive Paste for Anchoring and Crack Repair, 8.6 oz Cartridge, GrayThis two-part epoxy creates a paste when mixed that can be used to fill cracks. To use, mix then apply with a trowel. Once mixed, it creates a tacky paste that adheres well to most concrete surfaces, whether horizontal or vertical.

Keep in mind that it does have a short working time of 20 minutes before it becomes too dry to work with, so you’ll need to move quickly once the two parts are blended. The paste cures in just 4 hours. Once dry, the paste creates a flexible seal that resists cracking by expanding and contracting with the floor.

How to Fix Hairline Cracks in Basement Floor

Fixing a hairline crack that’s less than 1/4-inch wide on a basement floor is in some ways more challenging as it can be difficult to push the concrete patch inside of the crack. Use a liquid concrete repair product that is thinner and therefore capable of getting into the crack and conforming to it.

How Can I Prevent Concrete Floor Cracks?

Yes and no. Some forces are beyond your control, but there are some ways to prevent cracks from forming in the pavement. First, ensure that the earth below and around your foundation does not become saturated with water by fixing any grading problems causing drainage issues around the foundation.

Also, check your gutters to make sure they are functioning properly and downspouts to make sure they aren’t dumping water along the foundation. These measures can prevent the soil beneath from swelling, collecting so much water that it causes frost heave.

For newer homes, make sure to keep the temperature and humidity level in the basement in check as the concrete floor fully cures (a process that can take a year) to prevent the floor from drying too quickly, which can cause cracks.


More often than not, cracks in the basement are nothing to be alarmed about. They are usually caused by the normal wear and tear–a house settling or foundation concrete drying. When cracks do appear, repairing them is crucial to prevent water seepage, pests, and harmful gases in the soil below from entering the home.

Repairing a crack in the basement floor is a relatively simple process that can be accomplished with a concrete repair patch or sealant.

That said, be aware that some cracks are a sign of bigger problems. Heaving cracks caused by swelling earth or tree roots can cause structural damage that requires a professional to assess and repair.

Written By: Yevgen

YevgenI'm a DIY nut, and the founder and chief editor here at Weekend Builds.
This site is a result of my DIY passion, and to share the joys I have experienced fixing, building, and creating things over the years.

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