How to Fix Cracked Slab Foundation – 2 Methods

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Do you have cracks in your home’s foundation? These cracks let water and moisture into your home that may lead to damage, which is why you would want to know how to fix a cracked slab foundation.

If the cracks are smaller than 2mm, these cracks in the concrete slab are unsightly and can cause the home value to lower if you’re planning on selling. Left unchecked, they tend to let in moisture so you may end up with costly repairs. So if you have a cracked slab foundation, be sure to cover it up so that moisture doesn’t get in.

You’ll need a concrete crack repair kit.

20' Fast Set Concrete Foundation Crack Leak Repair Kit, Stop

Read on for how to fix it as soon as possible.

If cracks are larger than 2mm, you’ll want it looked over by a foundation crack specialist to rule out any serious foundation issues. You can also look around the house for signs of foundation issues, such as countertops that are pulling away from the wall. Small cracks could just be moisture issues, but larger cracks are concerning.

How to Fix Cracked Slab Foundation

How to Fix Cracked Slab Foundation

Here are the steps to fix small cracks in the concrete slab foundation.

Method 1: How to Fix Cracked Slab Foundation with Injection Epoxy Sealer

While a hydraulic cement sealant can help with minor cracks, an epoxy sealer is a better option. Epoxy resin comes in either an injectable or pourable form. That allows you to pick the application method that is more suitable for your particular situation.

There are a variety of epoxy-injection systems on the market to choose from. You can also find epoxy included in concrete repair kits along with plastic injection ports for delivering a sealant deeper into the cracks.

Step 1: Check the Crack and Dry It if Needed

First, you need to inspect the damaged area. If you notice a slightly damp crack, use a hairdryer to pull out moisture. If the water still seeps into the foundation crack, the dampness will return, so wait until it dries out itself.

Grab a wire brush and scrub the crack(s) clean of old filler if any, paint, and spalling concrete. Besides, use a shop vacuum to remove any dust, dirt, and unwanted particles.

Step 2: Drive a Few Nails into Cracked Slab Foundation

Before inserting injection ports, you need to block them out with 10d finish nails. Hammer the nails into the foundation so that they are spaced about 10 inches apart and driven partway into the crack(s). That will make sure the injection ports line up with the crack.

Step 3: Stir the Epoxy Resin

You will need a concrete crack repair kit for this job. As you may already know, the 2-part epoxy compounds come in two containers. Mix the equal amounts.

After opening the containers, scoop out the resin side (Part A) and the hardener (Part B). To avoid contamination, use a separate epoxy mixing stick for each part. The goal is to get a uniform gray color.

Step 4: Attach the Plastic Ports

Apply some epoxy resin on the base of an injection port. Be careful while doing this to avoid plugging up the hole. Once done, install the plastic ports (one by one) by sliding them over the finishing nails and pressing them to the slab foundation.

Step 5: Apply Crack Sealant

At this stage, you need to mix up a large batch of sealant and cover the entire crack with it using either a margin trowel or putty knife. Spread epoxy along the crack so that it’s roughly 1/8 inches thick.

Additionally, you should apply the crack sealant over the flange of every single port. Make sure they are entirely covered while the neck portions are visible. Once you’ve smoothed out the crack sealer, dip a paintbrush into mineral spirits and carefully feather the edges.

Step 6: Fill the Crack

Now you can seal up the crack. But before injecting the epoxy sealer into the gap, let the sealant cure. It takes about 8 hours.

Once it has cured, take the plunger rod (it is included in the repair kit) and mix the epoxy thoroughly. After placing the cartridge into a caulking gun, dispense the sealer into the foundation crack.

Step 7: Seal Up Each Injection Port and Let It Cure

Plug up all the ports after filling them up. Take the cartridge tip and insert it into the injection port. Simply dispense the epoxy by squeezing the trigger. This procedure should be repeated for the remaining crack ports.

Step 8: Remove the Ports and Smooth out the Foundation

Allow the epoxy to cure, which takes 5-6 days. Then remove the injection ports by cutting them away (the parts that protrude from the foundation) with a hacksaw.

What about the severed injection ports? Patch them with a crack sealer. If desired, smooth the slab foundation using an angle grinder. This will make the crack barely visible.

Method 2: Fix Cracked Slab Foundation with Slabjacking or Mudjacking

If the crack is the result of the sinking of your concrete foundation, then your best bet is to fix it with mudjacking (also known as slabjacking). Basically, this is concrete lifting. It is intended to lift and level settled concrete.

This method is best carried out by a professional. This step by step is an overview of how it would be done.

You need to make multiple drill holes into the slab foundation and fill them with a mud-like mixture. By pumping the grout, you will lift your slab to the desired height. For your better understanding, this method will be explained in three steps.

Step 1: Drill the Holes

First, you need to make a few drill holes. The larger slab, the more holes. A triangular pattern is often used for large slab foundations. Don’t overdo things.

When it comes to spacing, it will depend on the thickness of your slab. The holes should be drilled farther apart in case of thick slabs, and vice versa. They are 3 to 8 ft. apart in most projects.

As for the size of the holes, the smaller the better. At the low end, the holes should be only one inch in diameter. At the upper end, the range shouldn’t be larger than two inches.

Step 2: Pump the Grout

Once you’ve drilled the holes, it’s time to go to the next step – grout pumping. Start at the lower point of your slab. The grout will do wonders for your cracked slab foundation.

As your slab starts to rise slowly, you should move from hole to hole. Move back when you get to the last hole and repeat this process.

For larger foundations, you may need to make additional holes. They are supposed to support the slab while it lifts up. Fill them with more fluid, less dense grout to let it flow easily.

Step 3: Patch the Holes

Remove remaining grout. Then patch the holes by filling them with a mortar mix. Make sure it is stiff enough. Eventually, the surface of your slab should be smooth and clean without any signs of patched holes.

To make the repairs less noticeable, drill the cores instead. You should code and glue the cores after mudjacking. Keep in mind that this process is more expensive and very slow.

FAQs About How to Fix Cracked Slab Foundation

Is It Possible to Fix a Cracked Slab Foundation?

Yes, many people can successfully fix shallow or thin foundation cracks themselves. However, seemingly small cracks in the foundation often indicate large structural problems that can only be repaired by professionals.

What Is the Cost of a Slab Foundation Repair?

It depends on the type of problem. Expect to pay about $500 for minor foundation repairs and more than $5,000 for the serious issues and huge cracks that require hydraulic piers.


Foundation cracks can be a structural problem that is often caused by poor soil conditions, too much weight, or shifting of the foundation. Cracks larger than the thickness of a credit card should be looked at by a foundation crack specialist to find out how to fix cracked slab foundation and to prevent it from causing more serious problems to the house.

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