How Epoxy Foundation Crack Injection Works
Epoxy injection is a precision repair process. When done correctly, the epoxy penetrates the full depth of the crack and cures to a rigid, high-strength bond.
Step 1: Crack Assessment
The contractor examines the crack to determine:
- Is the crack active (still moving) or stable?
- Is moisture present or has the crack leaked?
- What is the crack’s width, length, and estimated depth?
- What caused the crack? (Settlement, lateral pressure, shrinkage, thermal)
Active cracks and wet cracks are not candidates for standard epoxy injection. For pricing by crack type and repair method, see the foundation crack repair cost guide.
Step 2: Surface Preparation
The crack face is cleaned of any loose material, paint, efflorescence, or moisture. A clean, dry surface is essential for epoxy adhesion.
Step 3: Port Installation
Surface ports (injection ports) are bonded to the concrete surface at intervals along the crack - typically every 8-12 inches for a standard wall crack. Port spacing determines whether the epoxy achieves full penetration.
Step 4: Surface Sealing
Epoxy paste is applied along the entire visible crack face between ports to seal the surface and contain the injection pressure inside the crack.
Step 5: Epoxy Injection
Starting at the lowest port (for horizontal or diagonal cracks) or the bottom (for vertical cracks), the contractor injects epoxy at low pressure (typically 20-40 psi). Injection continues at each port until epoxy appears at the next port above - indicating the crack section is fully filled. Ports are capped sequentially as filling progresses.
Step 6: Cure
Standard low-viscosity epoxy cures to handling strength in 3-5 hours at normal temperatures and achieves full structural strength in 24-72 hours. High-viscosity epoxy used for wider cracks has a similar or longer cure window.
Epoxy vs. Polyurethane Injection: Choosing the Right Material
| Factor | Epoxy Injection | Polyurethane Injection |
|---|---|---|
| Primary purpose | Structural repair | Waterproofing / sealing |
| Bond strength | Stronger than concrete | Flexible, non-structural |
| Works on wet cracks | No - requires dry surface | Yes - reacts with moisture |
| Works on active cracks | No - will re-crack | No (but fails more slowly) |
| Crack width range | 0.002-0.5 inch | Wide range |
| Cure time | 3-72 hours | Minutes to hours |
| Cost per crack | $300 - $800 | $250 - $600 |
Use epoxy when: The crack is dry, stable, and structural integrity is the concern. Common on poured concrete walls that have cracked but are not leaking.
Use polyurethane when: The crack is leaking or wet. Polyurethane reacts with moisture and can be injected into a wet or actively leaking crack. It seals the crack but does not restore structural strength.
Use both when: A leaking crack needs both waterproofing and structural repair - polyurethane is injected first to stop the water, and epoxy is injected after the crack has dried out.
What Types of Cracks Can Be Repaired with Epoxy
Good candidates:
- Vertical or diagonal shrinkage cracks in poured concrete walls (common in new construction, usually benign)
- Stable settlement cracks that have not changed in 1-2 years
- Cracks from thermal cycling in walls without adequate control joints
- Narrow horizontal cracks in walls not showing signs of active lateral pressure
Not appropriate for epoxy:
- Active cracks: If the crack is still moving (the wall is still settling, or there is active lateral pressure from soil), epoxy will re-crack. Address the root cause first.
- Wide cracks (over 1/2 inch): Very wide cracks may require routing and patching or a more involved structural repair before or instead of injection.
- Horizontal cracks in basement walls: Horizontal cracking in block or poured walls under lateral soil pressure indicates bowing - a structural condition requiring carbon fiber straps, wall anchors, or excavation. Epoxy injection alone is not the appropriate repair.
- Cracks in block or brick foundations: Mortar joints and block faces do not accept epoxy injection the same way poured concrete does. These foundations have different repair requirements.
Cost of Epoxy Crack Injection
| Scope | Typical Cost |
|---|---|
| Single crack (contractor) | $300 - $800 |
| 2-3 cracks, single visit | $600 - $1,500 |
| 4-6 cracks, full basement assessment | $1,200 - $2,500 |
| DIY kit (single crack) | $50 - $150 |
Factors that increase cost:
- Long cracks (over 6 feet) requiring more ports and material
- Tight access (low crawlspace, finished basement requiring panel removal)
- High-viscosity epoxy for wider cracks
- Pre-injection waterproofing required (wet crack)
Limitations: What Epoxy Injection Does Not Fix
Epoxy injection repairs the crack. It does not address what caused the crack. If the cause is ongoing, new damage will occur:
- If the crack was caused by foundation settlement, and the settlement has not been stabilized, new cracks will form.
- If lateral soil pressure is bowing the wall, injection alone does not stop the movement.
- If drainage problems are saturating the soil adjacent to the wall, the hydrostatic pressure will eventually crack the wall again.
A complete foundation crack assessment should include evaluation of the cause, not just the symptom. A contractor who injects the crack and says the job is done without discussing the cause is not giving you the full picture.
Getting a Quote
When getting quotes for epoxy crack injection, ask:
- What is the cause of this crack?
- Is this crack active or stable?
- Are there signs of moisture that would prevent epoxy from bonding correctly?
- What is included - injection, port removal, and surface finishing?
- What is the warranty on the injection repair?
Reputable foundation contractors will inspect the crack in person and discuss the cause before recommending injection. A phone quote for crack injection is rarely accurate.