Short answer
Epoxy injection can bond a crack back together and restore strength, but only if the crack has stopped moving. ACI says that unless the cause of cracking is corrected, new cracks will probably form near the original one. A moving crack needs the movement fixed first. A crack that only leaks often suits a polyurethane grout instead.
Key facts
- ACI 224.1R-07: cracks as narrow as 0.002 inch (0.05 mm) can be bonded by injecting epoxy.[1]
- ACI 224.1R-07: unless the cause of the cracking has been corrected, new cracks will probably form near the original crack.[1]
- ACI RAP-1: cracks caused by corroding reinforcing steel should not be repaired by epoxy injection because continuing corrosion will cause new cracks.[2]
- HomeGuide puts professional crack injection at $250 to $800 or more per crack (2025 and 2026 guides).[4]
What epoxy injection does
Epoxy injection pumps a two-part resin into a crack under pressure. The crew seals the surface of the crack, sets small ports along it, and injects until the resin fills the crack. The American Concrete Institute (ACI) says cracks as narrow as 0.002 inch (0.05 mm) can be bonded this way[1]. ACI's field guide says the main goal is "to restore the structural integrity and the resistance to moisture penetration" of the concrete[2].
For structural repairs, ACI says the epoxy should meet ASTM C881 Type IV, the load-bearing grade[1]. Ask what product and type your contractor plans to use.
What it does not do: stop movement
This is the most important point, and it is often left out of sales pitches. ACI 224.1R states: "Unless the cause of the cracking has been corrected, however, new cracks will probably form near the original crack"[1]. ACI's field guide is just as direct: "If the crack is subject to subsequent movement, an epoxy repair may not be applicable"[2].
Epoxy glues the two sides together. If the soil under a slab keeps moving, the slab will crack again, often right next to the glued line. So for a house slab, the order is:
- Find out why it cracked (an engineer's evaluation).
- Fix the cause (drainage, leak, settlement, heave).
- Then decide whether the crack needs a structural bond, a seal, or nothing.
If the cause cannot be removed, ACI lists three options: rout and seal the crack and treat it as a joint; build a joint that takes the movement and then inject; or add support or reinforcement so the crack stops moving[1].
Is the crack active or dormant?
ACI says crack repair choices should consider "whether the cracks are active or dormant"[1]. An active crack is still opening, closing or shifting. A dormant crack has stopped. You find out by tracking it over time:
- Mark the crack ends and date them.
- Measure the width with a crack card at the same spot each month.
- Check for offset with a straightedge. NAHB guidance says cracks with significant vertical displacement may indicate a structural concern[3].
- Note other signs inside the house. NAHB guidance says cracks alone are not necessarily structural, but become more of a concern alongside sticking doors and windows or sloping floors[3].
Our crack assessment checklist lays out the steps. FPA notes that cracks in concrete become noticeable at about 0.04 inch (1 mm) wide[6], so a crack you can see clearly is not unusual by itself. See the crack width guide.
Epoxy vs polyurethane vs sealant
| Method | What it is for | ACI notes |
|---|---|---|
| Epoxy injection | Bonding a dormant crack; restoring strength | Not for cracks that will keep moving[2]; not for cracks from rusting steel[2] |
| Polyurethane (chemical) grout injection | Stopping water through a crack | "Bond strengths are typically low, so structural repairs are not made with chemical grouts"[1] |
| Rout and seal | Non-structural cracks in floors and pavements; active cracks with a flexible sealant | Common and simpler than injection; avoid cement grout[1] |
ACI's field guide adds that if a crack does not compromise structural integrity, "injection with polyurethane grouts or other nonstructural materials may be a more suitable choice"[2].
Water matters too. ACI says epoxy injection is not suitable for cracks that are actively leaking and cannot be dried out, except with certain moisture-tolerant epoxies, and that silt and water in a crack can reduce how well epoxy bonds[1].
Special cases
Rust cracks. ACI's field guide says cracks caused by corroding reinforcing steel "should not be repaired by epoxy injection because continuing corrosion will cause new cracks to appear"[2]. A straight crack with rust stains needs a corrosion repair designed by a qualified engineer.
Slabs on the ground. ACI warns that when injecting a slab on grade, the soil or base under it may or may not hold the resin in, and "uncontrolled injection can cause damage such as plugging a drainage system"[1]. Ask how the crew will contain the resin.
Shrinkage cracks. NAHB guidance says shrinkage cracks in slabs are expected, very common, and do not compromise structural integrity[3]. Many of them need no injection at all, just sealing if water or looks are a concern.
What it costs
HomeGuide puts professional crack injection at $250 to $800 or more per crack, and says epoxy works best for stable, non-moving cracks while polyurethane stays flexible (July 2025)[4]. Its February 2026 foundation guide lists epoxy or crack stitching at $250 to $800 per crack[5]. These are national figures. Crack length, access and whether flooring must come up change the price. If the crack is a symptom of movement, the injection is a small part of the total repair.
When to call a pro
- A crack with one side higher than the other, or one that keeps widening: call a structural engineer before any injection.
- New cracks along with sticking doors or sloping floors inside the house.
- Cracks with rust stains or spalling concrete.
- A crack that leaks water every time it rains: ask a qualified repair contractor about a water-stopping grout, after the drainage is checked.
More questions
Is flexible epoxy better for a crack that still moves?
Not really. ACI explains that a flexible adhesive in a thin crack behaves about as stiffly as a rigid one, because the surrounding concrete restrains it. It will not let the structure move much. For an active crack, ACI points to routing and sealing with a flexible sealant over a bond breaker.
Can I inject a foundation crack with a DIY kit?
Kits exist for small, dry, non-structural cracks. ACI says epoxy injection takes a high degree of skill, and a crack that may be structural needs an engineer to decide the repair first. Any crack with offset, widening or other distress is not a DIY job.
Sources
- ACI PRC-224.1-07 (224.1R-07): Causes, Evaluation, and Repair of Cracks in Concrete Structures, American Concrete Institute, Committee 224. Accessed 2026-10-06.
- ACI RAP Bulletin 1: Structural Crack Repair by Epoxy Injection (2003, reapproved 2009), American Concrete Institute, Committee E706. Accessed 2026-10-06.
- Misconceptions about the common crack (Builder Education Series summary), National Association of Home Builders (Walt Keaveny, PE, PG). Accessed 2026-10-06.
- How Much Does Foundation Crack Repair Cost? (dated July 9, 2025), HomeGuide. Accessed 2026-10-06.
- How Much Does Foundation Repair Cost? (dated February 6, 2026), HomeGuide. Accessed 2026-10-06.
- Guidelines for the Evaluation of Foundation Movement for Residential and Other Low-Rise Buildings (FPA-SC-13-1), Foundation Performance Association. Accessed 2026-10-06.
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