How To Fill Large Gaps In Your Foundation?

Large gaps in the foundation aren’t only unsightly, but they’re also safety hazards. So how can you fill these imperfections? We researched this concern for you, and here’s what we found.

Filling large cracks, holes, and other gaps in your foundation is possible. But the technique to use often depends on certain factors, such as the size and location of the imperfection. Some of these solutions are:

  1. Expanding foam filler
  2. Foam backer rod and urethane caulk

Take note that applying the appropriate technique still requires following the correct steps. So continue reading as we talk about the procedures to fill the gaps in your foundation in greater detail.

Worker filling gaps on the foundation using an expanding foam filter, How To Fill Large Gaps In Your Foundation?

Should You Fill The Gaps In Your Foundation?

Hairline cracks between 1/8 and ¼ inches shouldn’t cause significant worry. However, any gap that’s larger than that range might need immediate attention.

For instance, gaps that meet the basement floor and the foundation wall could increase in size over time. This imperfection usually happens as the foundation settles, which might cause the household to become lopsided.

Worker plastering the walls of the foundation

Failure to fix these cracks and gaps soon may lead to serious problems. Over time, the property may encounter issues like:

  • Framing problems
  • Roof issues
  • Doors and windows won’t have proper seals
  • Other structural concerns

How Do I Fill The Gaps In My Foundation?

A bandage to cover a crack

Before proceeding with any of the repair procedures below, take note of the following safety guidelines:

  • Have the issue assessed by a licensed professional: Allow an industry expert to give you a rough idea of what you need to do to restore your foundation's integrity and stability.
  • Plan the procedure: Avoid making random decisions that may jeopardize your property’s foundation.
  • Only use equipment and materials that are in good working condition.

Also, you may need to request help from another individual for the repair procedures. That way, you can finish the job faster than initially expected. Plus, it can be a safer experience, knowing that the other person will have your back if something amiss occurs.

Method #1: Expanding Foam Filler

This technique can be ideal for filling cracks and holes in foundation walls made out of plaster. If you’re dealing with this material, continue this operation by following these steps:

What You’ll Need

  • Large cloth or tarpaulin
  • Screwdriver
  • Small hammer
  • Spray bottle filled with water
  • Expanding foam filler
  • Bread knife
  • Quick-drying poly filler
  • Putty knife

Step-by-Step Guide

  1. Lay the cloth or tarpaulin on the floor near the job site.
  2. Remove loose plaster by whacking a screwdriver with a small hammer.
  3. Clean the offending area with a soft-bristled brush.
  4. Use the spray bottle to moisten the work area with water.
  5. Spray the expanding foam filler into the gap.
  6. Allow the product to dry and cure, which may take about 12 hours to complete.
  7. Cut as much of the excess foam with a bread knife.
  8. Make the foam flush with the foundation wall by sanding it down.
  9. Apply quick-drying poly filler over the flattened foam.
  10. Smoothen the filler layer with a putty knife.
  11. Let the poly filler dry and cure before sanding it down.

Check out this expanding foam sealant on Amazon.

Don’t forget to protect yourself from the chemicals in the products you’re using by wearing safety gear. Also, watch the video below for a visual guide to this procedure:

Method #2: Foam Backer Rod And Urethane Caulk

Also called polyurethane sealant, urethane caulk is a solvent-based sealer that offers different advantages. Apart from sealing a large gap in the foundation, this product has:

  • Tear and water resistance
  • Low shrinkage
  • Paintable finish

Warning: Urethane caulk might not be ideal for filling gaps in the foundation of the offending area that gets hit by direct sunlight. Otherwise, UV degradation may occur, which might reduce the product's efficacy.

After taking note of that precaution, and deeming it safe to continue this procedure, continue by following these steps:

What You’ll Need

  • Urethane caulk
  • Caulk gun
  • Foam backer rod
  • Spoon
  • Sandpaper

Step-by-Step Guide

  1. Place the foam backer rod into the gap and ensure that it’s about ¼-inch deep into the crevice.
  2. Install the urethane caulk into the caulk gun.
  3. Apply urethane caulk over the foam backer rod.
  4. Smoothen the product with the spoon. Make sure that the product is flush with the foundation.
  5. Allow the urethane caulk to dry and cure, which can last about seven days.
  6. Sand any sealant to even it out.

Check out this polyurethane sealant on Amazon.

Apart from these methods, you can also read our post on what to do if you see a gap between the siding and the foundation for additional insight.

Why Is There A Gap In The Foundation?

A hole on the side of the house foundation

Gaps in the foundation may appear because of different reasons. Some possible suspects are:

Water Pressure

Flooding in the basement could cause unnecessary water pressure to the foundation wall. The additional moisture may push against the foundation, distorting the wall beyond safe parameters.

This event can lead to large gaps if left unchecked. It may also result in the removal of sealants, which might deliver the excess water to other areas on the property.

Poor Construction

Failure to use the right materials for the home’s construction can lead to major gaps in the foundation. Quality building materials are a must to help protect the house and its residents from accidents and injuries.

Expansive Soil

Some types of soil expand when they receive a significant amount of moisture. At times, minerals, such as vermiculite and certain sulfate salts, may cause the soil to expand. If so, the earth may push against the foundation, causing cracks and other gaps.

Natural Calamities

Earthquakes are often the primary culprits of foundation cracks. The earth's rapid shifting within an area may cause the foundation wall to rattle and sway beyond its safe limits. Aside from earthquakes, landslide pressures and sinkholes may also result in similar effects to a property's foundation.

Large Trees

In particular, the roots of some large trees may grow and apply unwanted pressure to the foundation. Also, the roots may absorb significant moisture from the ground, reducing the home's foothold on the earth. It may lead to the foundation shifting, which can also result in gaps appearing in the nearby wall.

Read our post on what to plant around the house foundation if you need help in ensuring the safety of your home while developing a lovely garden.

How Much Does It Cost To Fix A Gap In The Foundation?

Worker mixing concrete for plastering a wall

Foundation gap repair expenses can range from $250 to $800. Property owners may save some cash from the overhead by fixing fairly small cracks from their homes’ foundations. However, the costs may also skyrocket if major renovations become a requirement to help prevent further harm to the foundation.

What Is The Best Concrete Joint Filler?

A concrete joint filler can also be a good choice for sealing gaps in a concrete foundation. But it can be challenging to choose among different selections. Still, you can boil your options down to two main types: epoxy and polyurethane.

Worker plastering a concrete wall

Take note that both epoxy and polyurethane concrete joint fillers have some unique properties. These traits make these choices excellent options based on certain conditions.


Both epoxy and polyurethane fillers share similar scores in the durability tests. You can use a shore durometer to check the durability of these products if you’re curious about these numbers.

Temperature Resistance

Epoxy joint fillers often have trouble drying and curing when exposed to freezing temperatures. So it’s not often ideal to use these products in locations with cold climates like Minnesota, Maine, and North Dakota.

On the other hand, polyurethane fillers can dry and cure in inclement weather. That means you can use these products even when it’s winter.


Sometimes you might make mistakes with the application of the concrete joint filler. If so, some removal can be part of the repair process.

Epoxy fillers often provide more advantages over polyurethane in this department. It's because you can easily remove epoxy fillers by cutting them with sharp objects, such as a hand or circular saw. As for polyurethane, it may take more time and effort than expected to remove this substance.

Final Words

Worker filling gaps on the foundation using an expanding foam filter

Your choices of filling a large gap in the foundation vary. Choose among techniques like using expanding foam filler, urethane caulk, or a backer rod. Make sure to apply the appropriate steps regardless of the technique you choose to use. That way, you can prevent additional cracks and other imperfections from appearing in your foundation’s wall.

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