The short answer
Assess the Crack First
Before you buy any filler, look closely at the crack. Measure its width and note whether it is growing. A crack that stays under a quarter inch and shows no vertical or horizontal shift is often cosmetic. Check both sides of the crack for signs of rust, efflorescence, or dampness, which suggest water is moving through the foundation.
If the crack is wider than a quarter inch, or if you see one side higher than the other, the foundation may have settled. That kind of movement is not something you patch over. You need a professional evaluation to determine whether the soil under your home is shifting. Watch for water pooling near the foundation after heavy rain, as that can signal drainage issues.
- Measure crack width with a tape or caliper
- Look for vertical displacement between edges
- Check for moisture or efflorescence on the crack
- Note any recent changes in crack size
Choose the Right Repair Method
For hairline cracks, a flexible polyurethane sealant works well. It seals out moisture and moves with minor shifts. For slightly larger cracks, epoxy injection is stronger and bonds the concrete back together. Both methods require a clean, dry crack to adhere properly. Use a wire brush or vacuum to remove loose debris before applying anything.
If the crack is actively leaking water, you need a different approach. Water pressure behind the foundation can push out any surface patch. In that case, you might need a hydrophilic polyurethane foam that expands and stops the leak. That type of repair often requires drilling ports into the crack, which is harder to do without the right tools.
- Clean the crack thoroughly before sealing
- Apply sealant in dry conditions
- Use epoxy for structural bonding
- Consider foam injection for active leaks
Gather the Tools You Need
A basic repair kit includes a wire brush, a vacuum, a caulking gun, and the chosen filler. For epoxy, you also need a mixing container and a trowel. For injection, you need a caulk tube with a nozzle that fits into the crack. Wear gloves and goggles, especially when handling epoxy resins, which can irritate skin.
If the crack is on the interior wall, check for plumbing lines nearby before drilling or chiseling. A stud finder or a simple knock test can help you avoid pipes. If you are unsure about what is behind the wall, call a pro. A mistake here can lead to a bigger water damage issue, which is more expensive to fix.
Apply the Repair Step by Step
Start by widening the crack slightly with a chisel or grinder to create a V shape. This gives the filler more surface to grip. Vacuum out all dust and debris. If you are using epoxy, mix only the amount you can apply in the working time listed on the label. Force the filler into the crack with a putty knife, then smooth the surface.
For polyurethane injection, you inject from the lowest point and work upward, letting the foam expand and fill the void. After the material cures, trim any excess with a utility knife. Let the repair dry completely before painting or waterproofing over it. In humid climates, curing may take longer, so give it extra time.
Know When to Call a Pro
You can handle small cracks, but some situations are beyond DIY. If the crack is wider than half an inch, if it is caused by tree roots, or if your doors and windows are sticking, the foundation may be moving. A pro can assess the soil, drainage, and structural integrity. They can also recommend foundation stabilization if needed.
If you notice water intrusion through the crack, that is a water damage issue. Local water damage pros can dry the area and identify the source of moisture. They may also suggest foundation waterproofing to prevent future leaks. The cost of a professional repair depends on the crack size, access, and the method used, so get a clear assessment before deciding.
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Call Now (817) 799-6732Frequently asked questions
Can I use caulk to fill a foundation crack?
Caulk works for very small, non-structural cracks, but it is not a permanent fix. It may crack or pull away as the foundation moves. For a lasting repair, use a polyurethane sealant or epoxy that flexes with the concrete. If the crack is large or leaking, call a pro.
How do I know if a foundation crack is serious?
Look for signs like water seeping through, a crack wider than a quarter inch, or one edge higher than the other. Also check if doors or windows stick, which can indicate shifting. If you see any of these, have a professional inspect it. Small, stable cracks are usually cosmetic.
Should I repair foundation cracks before waterproofing?
Yes, always repair active cracks first. Waterproofing over a crack will not stop water from coming through. The crack needs to be sealed properly, either with a flexible sealant or injection foam. Once the repair cures, you can apply a waterproof coating to protect the foundation from future moisture.