Types of Foundation Cracks (and What They Mean)
Not all foundation cracks are equal. Before reaching for a repair kit, you need to identify what type of crack you're dealing with — because the type determines the severity, cause, and correct repair method.
Vertical Cracks
Run straight up and down (or within 30 degrees of vertical). The most common type — caused by concrete shrinkage during curing or minor settlement. Severity: Low. Usually cosmetic and easy to DIY repair. These are rarely structural concerns unless wider than 1/4 inch.
Diagonal Cracks
Run at a 30-75 degree angle, usually from a corner of a window or door. Caused by differential settlement — one part of the foundation sinks more than another. Severity: Low to Moderate. Minor diagonal cracks are repairable, but widening diagonal cracks may indicate ongoing settlement.
Horizontal Cracks — Most Dangerous
Horizontal cracks are the most structurally significant type. They indicate lateral soil pressure pushing against the foundation wall — often from expansive clay soil, frost heave, or hydrostatic water pressure. A horizontal crack means the wall is bowing inward and may eventually fail. Do not attempt DIY repair. Contact a structural engineer immediately. See our horizontal foundation crack repair guide for details.
Stair-Step Cracks
Follow the mortar joints in block or brick foundations in a stair-step pattern. Caused by settlement or lateral pressure. Severity: Moderate to High. Stair-step cracks wider than 1/4 inch or those with wall displacement require professional evaluation.
Hairline Cracks
Extremely thin cracks (under 1/16 inch) that appear within the first year after construction. Caused by normal concrete curing and shrinkage. Severity: Very Low. These are almost always cosmetic. Repair only if they allow water intrusion. Flexible concrete caulk is usually sufficient.
When Is a Foundation Crack Serious?
Use this checklist to assess whether your foundation crack needs immediate professional attention or is safe to monitor/DIY repair:
Safe to DIY Repair
- ✓ Vertical cracks under 1/4 inch
- ✓ Hairline cracks (under 1/16 inch)
- ✓ Crack hasn't grown in 6+ months
- ✓ No wall displacement (sides are flush)
- ✓ Single isolated crack
Call a Professional
- ✗ Horizontal cracks (any width)
- ✗ Cracks wider than 1/4 inch
- ✗ Crack is growing or widening
- ✗ Wall displacement (one side higher)
- ✗ Sticking doors/windows nearby
- ✗ Multiple cracks on same wall
Pro Tip
DIY Foundation Crack Repair: Step-by-Step
For vertical or diagonal cracks under 1/4 inch that aren't growing, you can make a permanent repair with an injection kit. Here's how:
Safety Warning
Wear safety glasses and chemical-resistant gloves when working with epoxy or polyurethane. Work in a well-ventilated area. Epoxy is exothermic — it generates heat as it cures. Do not mix large batches. Keep away from skin and eyes.
Choosing Your Repair Material
| Material | Best For | Strength | Water OK? |
|---|---|---|---|
| Epoxy Injection | Structural repair, dry cracks | Stronger than concrete | No — crack must be dry |
| Polyurethane Foam | Waterproofing, wet/active leaks | Flexible, no structural value | Yes — cures in water |
| Hydraulic Cement | Quick patches, active leaks | Moderate | Yes — sets underwater |
| Carbon Fiber Strips | Reinforcing bowed walls | Very high tensile strength | N/A — surface applied |
Clean the crack thoroughly
Use a wire brush to scrub loose concrete and debris from the crack. Follow with a shop vacuum to remove all dust. For cracks with efflorescence (white mineral deposits), use a muriatic acid solution diluted 10:1, then rinse thoroughly and let dry. The crack must be clean for any repair material to bond properly.
Install injection ports
Tap plastic injection ports (T-shaped) into the crack every 6-12 inches. For hairline cracks, space ports 6 inches apart. For wider cracks (up to 1/4 inch), space them 12 inches apart. The ports must be firmly seated in the crack so they don't blow out during injection.
Seal the crack surface
Mix the two-part epoxy surface paste and spread it over the entire visible crack between ports, about 1/8 inch thick and 1 inch wide. This seal keeps the injection material inside the crack. Cover the area around each port too, leaving only the port tips exposed. Let the surface seal cure for 4-6 hours (or per kit instructions).
Inject the repair material
Starting at the lowest port, attach the injection gun and inject slowly until material oozes from the next port above. Plug the current port with the included cap, move up, and repeat. Work from bottom to top so gravity helps fill the crack completely. For polyurethane, expect significant expansion — inject slowly and don't overfill.
Cure and finish
Allow epoxy to cure 24-72 hours depending on temperature (longer in cold weather), or polyurethane to cure 1-2 hours. Snap off the injection ports flush with the wall surface. Sand the remaining epoxy paste smooth if desired. The repair is now waterproof and, with epoxy, stronger than the original concrete.
Your foundation crack is now sealed and waterproof. For epoxy repairs, the bond is stronger than the original concrete.
Best Foundation Crack Repair Products
These are the most effective and well-reviewed products for DIY foundation crack repair. We recommend keeping one injection kit on hand for any homeowner with a basement.
RadonSeal DIY Foundation Crack Repair Kit
$34 – $65Polyurethane foam injection kit. Ideal for wet cracks and active leaks. Includes 10 ports and enough material for 10 ft of crack.
- Cures in wet conditions
- Expands 20x to fill voids
- 10 ft coverage per kit
- Includes injection ports & gun
Applied Technologies Concrete Crack Injection Epoxy
$50 – $90Professional-grade two-part epoxy injection system. Creates a structural bond stronger than concrete. Best for dry, stable cracks.
- Structural strength repair
- 3,000+ PSI bond strength
- Professional formula
- Covers 10 linear ft
Simpson Strong-Tie Crack Injection Repair Kit
$45 – $75Complete epoxy injection system from a trusted construction brand. Includes mixing nozzles, ports, and paste seal.
- Trusted brand in construction
- Complete kit with all supplies
- Works on cracks up to 1/4"
- Clear instructions included
Quikrete Hydraulic Water-Stop Cement
$8 – $15Fast-setting hydraulic cement for quick patches on active water leaks. Sets in 3-5 minutes, even underwater.
- Sets in 3-5 minutes
- Works on active leaks
- Budget-friendly option
- Available at all hardware stores
How Much Does Foundation Crack Repair Cost?
Costs vary dramatically based on crack severity and repair method. Here's what to expect for DIY vs professional repair:
Foundation Crack Repair Costs (2026)
| Repair Type | DIY Cost | Professional Cost |
|---|---|---|
| Hairline crack (< 1/16") | $10 – $25 | $150 – $400 |
| Minor crack (1/16" – 1/4") | $30 – $80 | $250 – $800 |
| Major crack (> 1/4") | Not recommended | $500 – $3,000 |
| Horizontal crack (structural) | Not recommended | $3,000 – $10,000 |
| Full wall reinforcement | Not recommended | $5,000 – $15,000 |
Costs are national averages. Actual costs vary by region, contractor, and specific conditions. Always get 3 quotes.
Professional Foundation Repair Methods
When cracks are beyond DIY repair, professionals use these methods — ordered from least to most invasive:
Carbon Fiber Reinforcement
Cost: $5,000 – $10,000 per wall · Carbon fiber strips or sheets are epoxied to the interior wall surface to prevent further bowing. Minimally invasive — no excavation needed. Best for walls that have bowed less than 2 inches.
Wall Anchors / Helical Tiebacks
Cost: $3,000 – $7,000 per wall · Steel anchors are driven through the foundation wall into stable soil outside, then tightened to stabilize (and sometimes straighten) the wall. Requires exterior access. Best for moderate bowing.
Pier Underpinning
Cost: $10,000 – $30,000+ · Steel piers are driven through the foundation down to stable bedrock or load-bearing soil. The foundation is then lifted and stabilized on the piers. The most comprehensive solution for severe settlement. Usually includes a transferable warranty.
When to Call a Professional
- Any horizontal crack (indicates lateral soil pressure)
- Cracks wider than 1/2 inch or rapidly growing
- Wall displacement — one side of the crack is higher than the other
- Bowing walls — the wall leans inward more than 1 inch
- Sticking doors and windows in rooms above the crack
- Multiple cracks on the same foundation wall
- Cracks accompanied by floor heaving or sinking
Foundation Crack Prevention Tips
The best repair is the one you never have to make. These preventive measures address the root causes of most foundation cracks:
Pro Tip
Pro Tip
Pro Tip
Pro Tip
Related Guides
Horizontal Foundation Crack Repair
Specialized guide for the most serious type of foundation crack.
Read GuideFoundation Crack Repair Cost
Detailed cost breakdown for every repair method and severity level.
Read GuideBasement Leak Repair
Complete guide to fixing basement water leaks and waterproofing.
Read GuideFrequently Asked Questions
Written by
HomeRepairBase Editorial Team
Our team of home improvement experts and licensed contractors creates detailed repair guides, cost breakdowns, and troubleshooting tips to help homeowners tackle structural issues with confidence.