The best way to fill a crack between a concrete slab and a wall is to start by measuring the size of the crack. It can be filled with urethane rubber if it is 6 mm or less. If the crack is larger than 0.25 inches, insert a foam bar and fill it with urethane rubber. After filling, smooth out the urethane with a spoon or caulking tool. Finally, remove excess caulk with mineral spirits.

Is it necessary to fill the space between the concrete slab and the Drywall?

If the gap between the wall and the slab is more than 0.4 inches, it must be filled. Similarly, it must be filled if the crack allows water to seep into the house or basement. Leaky cracks must also be filled if they are less than 0.4 inches wide. If you decide to fill the crack, using a flexible material, such as caulking, is essential. Filling the crack with concrete or other hard material can cause further cracks and damage the house.

If the space between the concrete slab and the wall is larger than 10 mm, it has to be filled (0.4″).

• Gaps smaller than 10 mm (0.4″) should be filled if they cause water leakage.
• In most cases, the space between the slab and the wall is intentional to allow for expansion and contraction of the concrete due to temperature.
• It is unnecessary to fill spaces of 0.4 inch or less that do not cause leaks.
• When filling the space between the slab and the wall, use flexible materials such as foam and caulk.

Houses are often built with expansion space between the concrete slab and the exterior walls. This space is intentional. It allows the materials in the house to expand and contract as the temperature changes. Without this space, expansion, and contraction would create cracks in the concrete. These spaces should be a maximum of 10 mm (0.4″). If the crack is within these limits and does not cause leakage, there is no need to fill it.

7 steps to fill the space between a wall and a concrete slab

Filling cracks between concrete floors and foundation walls are sometimes necessary to prevent water leaks or other damage. To tackle this task, follow these simple steps.

Measure the crack

Start by measuring the width of the crack. If the crack is 6 mm or less, it can be filled with caulk. This method is ideal for small cracks that cause leaks or cracks in the concrete slab. A simple ruler or tape measure can be used to determine the size of the crack. It is also a good idea to measure different areas of the crack in case it is larger in some places than others.

• Use a ruler or tape measure to determine the crack size between the concrete slab and the wall.
• Cracks less than 0.25 inches wide can only be filled with caulk.
• If the crack is at least 0.25 inches wide, it should be filled with foam rods and caulked.
• Measure the slot several times to determine if some sections are wider and need a foam rod.

If the crack is wider than 0.25 inches, it cannot be sealed with kaolin alone. Instead, a foam bar must support the caulking and provide a flexible seal. Again, knowing the type of work to be done will enable you to be successful.

Gather tools and materials.

• Once you have measured the space to be filled, it is time to prepare to fill the space. The following are needed for this job.
• This urethane caulk.
• A caulking gun.
• If the gap is larger than 6 mm (0.25 in.), this foam bar with a diameter corresponding to the width of the gap.
• A spoon or caulking tool.
• Mineral liquid.
• Disposable gloves of your choice.

Urethane mastic is the best choice for this job because it is tear-resistant, weather-resistant, and adheres well to concrete and stone. Polyurethane is also a good choice. Avoid using silicone to fill voids in concrete. It needs to be stronger for this purpose.

Press the foam backing into the crack.

If the gap to be filled is 6 mm or more, it is necessary to fill it with foam before applying the mastic. To do this, first, measure the length of the crack. Then cut the foam rod to the correct size. Then press the foam rod into the gap.

• Grooves wider than 6 mm should be filled with foam rods before mastication.
• Cut the support rod to the length of the gap.
• Push the support rod into the slot until it is 0.25 cm below the concrete slab’s surface.

The rod should be fully inserted into the slot. It should be 6 mm below the surface to allow proper sealing and waterproofing. To avoid damaging the reinforcing rod, use the handle of a screwdriver or other blunt instrument to drive it firmly into the crack.

Lining the groove

Before chewing:

1. Put on a pair of disposable gloves.
2. Cut the end of the urethane chewing tube at a 30-degree angle to release the chew.
3. Insert the tube into the gun and fill the groove.
4. Work slowly from side to side. The mastic should fill the groove and completely cover the foam backing rod.
5. Wear disposable gloves when working with urethane putty.
6. Cut the end of the urethane mastic tube for application.
7. Load the mastic into the mastic gun and fill the groove.

No part of the foam backing rod should be visible through the mastic.

The mastic must not spill over the crack. Cracks should be grouted to create a smooth, watertight barrier between the board and the wall. It is optional to fill the crack.

Sealing small cracks

Once you have sealed the main crack between the concrete slab and the wall, take the opportunity to seal any other small cracks you see in the concrete foundation. It’s a good idea to clean out any dirt or weeds growing in these small cracks and then seal them.

• Inspect the concrete slab for small cracks.
• Clean the cracks to remove dirt and weeds.
• Seal the cracks with the same urethane sealant used to seal the larger crack.
• Sealing small cracks prevents them from widening.

Sealing small cracks prevents the penetration of water, dirt, and ice that can widen the crack over time. Therefore, detecting small cracks before they widen can prevent future leaks and damage to your home.

Smoothing the Caulk

Once the caulk has been applied, it’s time to smooth it out to create a clean and durable seal. The best tool for this task is a spoon. Dip the spoon into mineral spirits and, using the back of the spoon, smooth and spread the putty until it is even.

• Dip a metal spoon in mineral spirits.
• Smooth the crack with the back of the spoon to create an even joint.
• Wipe the spoon with mineral spirits if the urethane sealant starts to stick.
• Wear gloves during this step to avoid skin contact with the mineral spirits and urethane putty.

A putty smoothing tool can be used for this job, but many of these tools are made for small putty joints. A trowel works best for a large gap between the tile and the wall.

Clean

Throw used grout tubes and gloves into a closed garbage bag. Then use mineral spirits to remove urethane rubber from all grout tools. Urethane is stubborn and sticky, but mineral spirits make cleanup easier.

• After use, discard used grout tubes and gloves.
• Clean the putty-off tools with mineral spirits.
• Use soap and water or industrial hand cleaners to remove urethane kaolin from the skin.

It is important not to use mineral spirits to clean urethane kaolin from the skin. Mineral spirits can cause skin irritation. If urethane kaolin stains your skin, wash it with soap and water or use our tips for removing roofing compounds from your hands. These tactics will also help you clean urethane kaolin off your hands. 

How to fill a gap between a wall and a concrete slab?

To fill a gap between a concrete slab and a wall, follow these steps:

• First, measure the width of the crack.
• If the crack is less than 6 mm (0.25 in.) wide, it can be filled with urethane mastic.
• If the crack is 6 mm (0.25 in.) or larger, fill it with reinforcing foam before masticating.
• Push the reinforcing foam reinforcement bar 0.25″ below the panel surface so the foam can be masticated.
• Chew the crack and any small cracks in the concrete slab.
• After chewing, smooth the chew with the back of a spoon.
• Clean tools with mineral spirits to remove grout. Use milder cleaners to remove grout from the skin.

It is important to note that houses are often built with an intentional gap between the board and the wall. A gap of 10 mm or less that does not cause water leakage should not be filled. However, larger cracks and cracks that allow water to enter the house should be filled.