Filling Gap Between Concrete Slab And Wall

Many homes have them, and the owners are not sure why there are there. Can you spot a gap between your concrete slab and the foundation wall? You may wonder why you have a gap between the slab and the foundation wall?

It is a design feature unless the gap between the slab and the foundation is more significant than 0.4 inches. If this is the case, you can use concrete caulk to fill the concrete and wall gap.

In our guide, any family handyman can learn more about sealing the gap between garage floor and wall and why it needs doing. By the end, you’ll see it doesn’t take many tools or materials to get a better finish in your home and seal the gap between concrete floor and wall. (Learn How To Fix Drywall Patch Marks Showing Through Paint)

concrete slab and wall

Why Is There A Gap Between Slab & Foundation Wall?

Cracks above door frames, a gap between slab and foundation wall, and cracks surrounding windows are common in a home with an incorrect arc.

Expansion joints are the gaps between your concrete patio or concrete steps and your house. These expansion joints are installed in your garden walkway, driveway, garage floor, and basement floor before the concrete is poured.

The goal of the expansion joints is to allow the two slabs to expand and contract freely in response to changing weather conditions.

During the summer, direct sunshine bakes the concrete or paving slab outdoors or on your patio, whereas the slab within your home is shaded. Therefore, it’s critical to fill the gap with a flexible material to absorb this motion.

During the winter, you’ll also need a substance that will prevent precipitation or water absorption between your patio slab and retaining wall.

However, you can discover that the ideal spacing between the slab and the foundation wall is 0.4 inches, and if the gaps fall inside, you’ll have no issues with your foundation wall.

Worries emerge when the gap is more significant than this as it shows your home has shifted and the poured concrete settled more than it should. At these times, you are best to seal the gap using various methods, so the wall and floor can expand and contract to cause no concrete cracks.

floor slab

Sealing The Gap Between Wall and Concrete Floor Slab

The gap between the slab and the foundation wall must be rectified immediately to prevent future concrete deterioration. Water can leak between the slab and the wall if the expansion gap is too large. To cover, you can add a skirting board once the gap is filled.

This gap allows dirt to accumulate, leading to yet another issue. A more significant expansion gap causes undesirable cracks in the concrete.

Fill up the space between the foundation wall and the slab before it worsens. You have two options for sealing it. One is a long-term solution, while the other is a temporary solution. (Learn How To Fill Gap Between Baseboard And Tile Floor)

Method #1 Caulking the Gap

Caulking is the sealing concrete cracks or gaps between the slab and the wall. This is an effective means of closing the deficit.

Water can enter the cracks and enlarge them if the gap is large enough. Hence, you need caulk to seal these cracks and gaps.

What You Need

  • Caulk gun
  • Masking tape
  • Spoon
  • Foam backer rod
  • Mineral spirits
  • Polyurethane caulk

1. Install Backer Rod

The backer rod is significant with concrete with wide gaps and keeps the caulk in place. Too much unsightly gap and the caulk will sink. Note that the foam backer rod must be inserted into the expansion gap. To ensure this tight fit, purchase one larger than the gap size.

To place the backer rod in the gap, use your fingers to push it along the gap where it can sit 1/4 inch below the concrete’s surface.

2. Tape Before You Caulk

It is essential to tape off the sides before caulking. Use your tape, as this helps the control of the caulk lines. Just remember to remove the masking tape once the caulk dries off.

3. Fill the Gap

With the backer rod inserted, it is time to fill the gap and cracks. Again, you can find many caulk alternatives available, although urethane caulk is ideal for filling expansion gaps.

Cut the caulk tube at a 30-degree angle equal to the gap size. Fill the gap between the slab and the wall in a smooth motion. To smooth the caulk, you can use an old family handyman trick of wetting your finger, or you can use the back of an old spoon.

Note: Caulk is sticky and can cause an allergic reaction in some people. If you get caulk on your skin, wipe it off using paint thinner and cloth as soon as possible.

To remove caulk off the spoon, wipe it with a rag and mineral spirits.

4. Cover Your Caulk

It’s time to conceal the gap between the concrete floor and the wall after you’ve sealed it. Cover the caulk with a concrete mix or self-leveling sealant to restore the floor’s appearance and direct water away from your home. (Learn How Long Does Silicone Caulk Take To Dry)

The concrete mix needs to be wet to sit on the dry caulk.

Method #2 Use Window Seal Tape To Fill Gap

Another simple way to fill the gap between the floor and the wall is to use this technique. You can use weather strips or window seal tapes to close gaps around the control joints of your floor and walls.

It is only temporary, and the chances are it will require a repeat application after a few months.

Using a stripping knife or large flathead screwdriver, you can push the strip into the gap between the foundation wall and the slab.

Ensure your tape matches the expansion gap thickness. The tape expands on its own and can quickly close the gap.

patio and house

Fill Gap Between Concrete Patio and House?

Caulking the gap between your concrete patio and where your home sits is one option. This is done to prevent water leakage from entering the concrete gaps and leaking inside your property. A patio will receive direct sunlight, and anything cement-based will expand in the heat.

What You Need

  • ¾-inch Closed cell backer rod
  • Spline roller
  • Pair of scissors
  • Concrete crack sealant
  • Caulk Gun
  • Flathead screwdriver


  1. Clean Gap: Remove any old material other than soil. Use a flathead screwdriver to remove the fiberboard then vacuum any debris.
  2. Determine Gap Size: Check the gap size to determine the size of the backer rod needed.
  3. Insert Backer Rod: Trim the backer rod using the scissors. Push the rod ¼ inch lower than the concrete surface. Use the spline roller to level the foam.
  4. Apply Sealant: Apply concrete patching compound crack sealant or your urethane caulk. If you want a waterproof concave lip between the patio and your house, a concrete crack sealant applied with caulk gun is the best option.
  5. Fill the gap: From the farthest corner apply to the gap based on instructions. Once you know the width of your sealant cover it with ⅛-inch layer of sand.
  6. Smoothen sealant: Using a plastic spoon, smoothen the sealant and seal the gap. To clean, use a rag and mineral spirits.
  7. Let Your Sealant Cure: Allow the sealant or caulk to dry for about 24 hours. Once the sealant hardens, brush off excess sand.

Installing Expansion Joints Between Concrete Slabs

The easiest way is to add an expansion joint material such as cork, backer rod, or plastic as you pour the concrete sections to prevent concrete cracks.

Using a joint trowel, you can also create a narrow space between slab sections. If the concrete slab was already poured and cured, an expansion joint could be added using a concrete saw.

Mark the width and depth of your expansion joint, and cut with the recommended saw. You use this on thin and narrow concrete surfaces such as sidewalks. (Read Wire Size For 100 Amp Panel Guide)

What Is a Cove Joint?

A cove joint is the intersection of your basement wall and floor. That a home’s foundation is poured creates it. After the foundation footings are erected, the basement walls are poured into a keyway. This keeps them aligned and prevents concrete cracks.

After the walls have dried, the basement floor is poured. This creates a cove joint or small gap between the floor and the walls.

Why a Cove Joint Leaks?

Groundwater near your property rises after heavy rains and pushes into any cracks in your foundation.

Water enters your foundation through the cove joint because it is structurally necessary. Long-lasting or severe rains will eventually force their way through these crevices. This is called hydrostatic pressure.

Why Not Seal the Gap Between Basement Floor and Wall?

Using urethane caulk in the cove joint may seem simple to keep water out of your property. But it’s not that easy.

A sealant put between the basement floor and wall may prevent leaks in the near term. However, it will ultimately fail in one of two ways:

The water that the sealant blocks will find another way into your home. This usually means foundation cracks.

Water will drive the sealant off or penetrate it. The water will then leak through the sealant, rendering it unusable.

Interior Drain Tile

While sealing the gap isn’t advised, there are ways to protect your house from water damage.

The most typical treatment for leaking cove joints is a drain tile system. This drain is beneath the floor of your basement. It functions like a gutter beneath your basement, reducing hydrostatic pressure and directing groundwater away from your basement that would otherwise leak in.

Interior drain tile systems comprise a flexible, perforated plastic pipe that allows water to enter. It connects to a sump pit, allowing your sump pump to force ground water out rather than allowing it to leak in through your cove joint. (Learn How To Unclog A Bathtub Drain)

Drain tile pipework is sometimes composed of clay. The overall diameter varies between a few inches and more than a foot.

An inside drain tile system has various advantages:

  1. First, it can be installed, causing no damage to your outdoor landscaping.
  2. It’s less expensive than several other types of exterior waterproofing.
  3. Finally, the risk of harm from the elements or roots is reduced.
  4. Membrane for Waterproofing on the Outside
  5. The foundation is waterproofed from the outside.

You can still protect your home from hydrostatic pressure if something prevents it from being waterproofed from the inside.

Professional waterproofing professionals install a waterproof membrane along foundation walls. This membrane protects foundations by coating it and adding a layer of protection to prevent leakage and moisture intrusion.

Filling Gap Between Concrete Slab And Wall (1)

Leave a Comment

Your email address will not be published. Required fields are marked *