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How Do You Repair a Foundation Crack That Is Leaking Water?

Last updated October 26, 2026

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The short answer

Stop the Water First

Before any repair, you need to stop water from pushing through the crack. Look for the source, such as poor drainage, a downspout dumping water near the foundation, or a high water table. Redirecting water away from the wall can reduce pressure and slow the leak.

If the leak is active, you may need to manage the water inside while you work. A sump pump or a wet vacuum can help keep the area dry. Do not attempt to seal a crack while water is actively flowing, as most sealants will not bond to a wet surface.

Prepare the Crack for Sealing

Once the area is dry, clean out the crack using a wire brush or a chisel to remove loose concrete, dirt, and old sealant. The crack should be widened slightly to create a V-shape, which gives the repair material a better grip. Vacuum out all dust and debris.

For larger cracks, you may need to use a grinder or a small chipping hammer to open the gap. This step is important because a clean, rough surface helps the sealant adhere. If the crack is hairline, you might not need to widen it, but you still need to clean it thoroughly.

  • Use a wire brush or chisel to remove loose material
  • Widen the crack to a V-shape for better adhesion
  • Vacuum out all dust and debris before sealing
  • For larger cracks, consider using a grinder or chipping hammer

Choose the Right Sealant

The two main types of sealant for foundation cracks are polyurethane foam and epoxy. Polyurethane expands to fill the crack and is flexible, making it good for moving cracks. Epoxy is rigid and strong, often used for structural repairs, but it may not flex with the foundation.

Your choice depends on the crack's size and whether it is still moving. A polyurethane injection is often used for active leaks because it reacts with water and expands. Epoxy is better for non-moving cracks that need structural strength. For most homeowners, the pros will select the right material based on the specific situation.

  • Polyurethane foam expands and flexes, good for active leaks
  • Epoxy is rigid and strong, a sensible choice for non-moving cracks
  • Injection methods force sealant deep into the crack
  • The right choice depends on crack width and movement

Inject the Sealant

For a proper repair, the sealant is injected into the crack under pressure, not just smeared on the surface. This is done using a caulking gun or a specialized injection pump. The goal is to fill the entire crack from the inside out, creating a watertight seal.

The pros often use a technique called low-pressure injection, which forces the sealant deep into the crack. This method works well for cracks that go through the entire wall. For a DIY approach, you can use a caulk gun with a narrow nozzle, but results may not be as durable.

Seal the Surface and Monitor

After the injection, apply a surface sealant over the crack to protect the repair and smooth the area. This can be a masonry caulk or a cement-based patching compound. Allow the repair to cure according to the product instructions before exposing it to water.

In many cases, the pros will assess the foundation and recommend the right long-term fix.

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Frequently asked questions

Can I fix a leaking foundation crack myself?

You can attempt a DIY fix for small, non-structural cracks using a polyurethane sealant from a hardware store. However, for active leaks or large cracks, the pros have the right tools and materials to inject sealant under pressure, which gives a more reliable result.

How long does a foundation crack repair last?

A proper injection repair can last for many years, but the lifespan depends on the cause of the crack and whether the foundation continues to move. If drainage issues are not fixed, water pressure may cause the crack to reopen. Regular inspection helps catch problems early.

Will my insurance cover foundation crack repair?

Policies vary, and your insurer decides what is covered. Water damage from a sudden event, like a burst pipe, may be covered, but gradual seepage through foundation cracks is often excluded. Check your policy and talk to your insurance company to understand your coverage.

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