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.
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.