Published 2026-05-01 · Madison Foundation Pros
Foundation Crack Repair: Polyurethane vs Epoxy (Which One You Actually Need)
Quick answer: Polyurethane injection runs $400 to $600 per crack and is the right fix for water intrusion through a non-structural crack. Epoxy injection runs $500 to $800 per crack and is the right fix when the concrete itself has failed and needs to be re-bonded as one monolith. In the Madison market, roughly four out of five residential cracks we inject are polyurethane jobs. Free inspection, written quote before any port goes on the wall.
What each resin actually does inside the crack
Polyurethane is hydrophobic and flexible. We pump it into the crack under low pressure, where it reacts with any trace moisture in the concrete and foams out to roughly 8 to 10 times its liquid volume. The expansion is what makes the seal work. The resin fills every void inside the crack, including the hairline branches that an injection without expansion would miss. Once cured, the polyurethane stays flexible enough to handle the eighth-inch of seasonal movement that most Madison-area block and poured walls show across the freeze-thaw cycle.
Epoxy is a structural adhesive. It bonds chemically to the cured concrete on both sides of the crack and, once it cures, the resin is stronger than the surrounding concrete itself. A wall repaired correctly with epoxy will fail next at a different location, not at the old crack line. The trade-off: epoxy is rigid. Any future movement in the wall will produce a new crack rather than reopening the old one. That can be the right outcome on a properly stabilized wall, but it is the wrong outcome on a wall that is still moving.
The Madison decision rule, in plain terms
Polyurethane if the wall is structurally fine and the problem is water. Epoxy if the concrete has failed and the wall needs to act as one piece again. That is the whole rule.
The follow-up question is how to tell which case you are in. The honest answer: you usually cannot tell from a photo. We can, after 60 seconds with a feeler gauge and a flashlight. A horizontal crack wider than 1/8 inch with offset between the two sides is structural, period. A vertical crack at a cold joint with efflorescence (the white mineral stain) and no offset is a water problem, period. The cases in between are the ones we walk through on the inspection.
When each one is the right call, by failure pattern
| What you see | Likely cause | Right fix |
|---|---|---|
| Vertical or diagonal crack, water seeping, no offset | Hydrostatic pressure at a shrinkage or cold-joint crack | Polyurethane, $400-$600 |
| Diagonal crack from corner of a window or door opening | Minor differential settlement, often stable | Polyurethane, $400-$600 (monitor for 12 months) |
| Horizontal crack mid-wall, no offset, slight bow | Clay-soil pressure beginning to push wall inward | Carbon-fiber strap plus polyurethane, $900-$1,400 total |
| Crack with quarter-inch offset between the two sides | Structural failure of the concrete, often active settlement | Epoxy plus wall anchor or pier, $1,200-$3,500+ total |
| Crack at corner with stair-step pattern in block wall | Settlement, foundation underpinning territory | Helical or push pier plus epoxy, $10K-$30K range |
Why Monona homes get polyurethane and Verona homes get a mix
Monona's housing stock is mostly 1950s and 1960s ranches with poured-concrete walls cast at lower strengths than current code. Every 8-foot pour break is a cold joint, and those cold joints are the predictable seepage point after 60 winters of freeze-thaw cycling. The cracks themselves are stable. The walls are not moving. The water is the problem. We run polyurethane injection on roughly nine out of ten Monona repair calls because the diagnosis matches the resin: a flexible seal for a wall that still expands and contracts seasonally but is not in active failure.
Verona is a different mix. The 2007-to-2012 buildout in Hawks Landing, Cathedral Point, and Liberty Square put homes on compacted-clay subgrade that the original builder graded to tract-construction standards. Fifteen to twenty years in, we see two failure types side by side. The first is the same hydrostatic crack pattern as Monona, polyurethane handles it, done. The second is active corner settlement that opens diagonal cracks with measurable offset. Those cracks get epoxy injection, but the epoxy is the cosmetic finish on top of the real fix, which is usually 4 to 8 helical piers along the affected wall.
What the injection looks like, step by step
- We scrub the crack face clean and apply surface ports every 6 to 12 inches along the crack length, bonded with a 5-minute epoxy paste.
- We seal the rest of the crack face with the same paste so the resin cannot escape during injection.
- We mix the resin (two-part for both polyurethane and epoxy) and inject under low pressure starting at the lowest port, working up.
- As resin appears at the next port up, we cap the lower one and move up. Each port gets injected until the resin holds back-pressure for 30 seconds.
Cure time on polyurethane is 4 to 6 hours before water testing. Epoxy needs 24 hours for full cure. We knock the surface ports off the wall the next morning, grind the residue flush, and the wall looks the same as it did before we showed up, except dry.
Local proof points from recent injection jobs
A Belle Isle home on the Monona side of Lake Monona, built 1958, came to us last June with three diagonal cracks running from cold joints on the south wall. Each crack was wet through every spring and stayed damp into July. Three polyurethane injections at $470 each, two hours on site, one return visit four hours later for water testing. Total: $1,410. The owner sent a photo of the dry south wall after the May 2026 melt season.
A Stoughton home in Norse Heights, 1973 build, showed a 1/4-inch offset on a diagonal crack running from the basement floor to the rim joist on the southwest corner. Active settlement, not a water problem. We injected the crack with epoxy at $720, but the real fix was four helical piers along the southwest corner at $1,800 each. The epoxy line item was 9 percent of the project total. We talk through that math on the inspection so the homeowner does not see a $720 epoxy injection as the whole answer.
A Pheasant Branch (Middleton) home built 2003 had a hairline vertical crack on the east wall, no water, no offset, the homeowner just did not like looking at it during basement finishing. We injected polyurethane at $440 for the cosmetic seal, ground the surface ports flush, and the crack disappears under primer and drywall now. Sometimes the fix is small and the budget reflects it.
When neither injection is the right answer
Injection seals a crack. It does not fix what caused the crack. If the cause is going to keep pushing on the wall, the crack will come back next to the old one within a year or two, and you will be paying twice. We refuse to inject in three situations, every time.
- Active bowing past 3/4 inch. The wall is going to keep moving. Injection will reopen. Stabilize first with carbon-fiber straps or wall anchors, then inject afterward if water remains.
- Quarter-inch-plus offset across the crack. The two sides of the concrete have moved relative to each other. That is structural. Pier the foundation, then epoxy the crack.
- Active water flow at injection time. The resin will not bond to a saturated concrete face. We come back after two weeks of dry weather, or we install an interior drain tile first to relieve the hydrostatic pressure.
A note on the warranty difference
Our polyurethane and epoxy injections both carry a lifetime warranty against the same crack returning. What the warranty does not cover: a new crack that opens within 12 inches of the old one. That is not a warranty failure, that is the underlying soil pressure picking a new path. We disclose that in writing on every quote because homeowners deserve to know that injection treats the symptom and not always the cause. Where the cause is the real problem, we will recommend the structural fix and explain why the injection is a $500 line item on a $12,000 project rather than the whole answer.
Frequently asked
Polyurethane or epoxy: which one does my crack need?
Pick polyurethane if water is the problem and the wall is structurally fine. Pick epoxy if the crack is a structural failure of the concrete itself and the wall needs to be re-bonded into one continuous monolith. About 80 percent of the residential cracks we inject in the Madison area are polyurethane jobs because the underlying issue is hydrostatic pressure pushing water through a non-structural shrinkage or cold-joint crack. The other 20 percent (active settlement cracks, impact damage, structural cracks above 1/8 inch) need epoxy and often need a wall anchor or carbon-fiber strap alongside it.
How much does each one cost in Madison?
Polyurethane injection runs $400 to $600 per crack installed. Epoxy injection runs $500 to $800 per crack installed. Most Madison-area homes need 1 to 3 cracks injected during a single visit, so the total typically falls between $400 on the small end and $2,400 on the heavy end. The injection itself takes 45 to 90 minutes per crack once the surface ports are bonded and the resin is mixed.
Will the crack come back after polyurethane injection?
The crack itself stays sealed because polyurethane expands and locks into the void permanently. What can change is the concrete around it. If the soil pressure that opened the original crack continues to push, the wall can develop a new crack within a few inches of the old one. That is why we always check for the underlying water and pressure cause, not just the crack. A 1908 Williamson-Marquette home we injected last year shifted the failure point 14 inches over within seven months, which told us the real fix was an interior drain-tile system, not another injection.
Can I inject a foundation crack myself with a hardware-store kit?
On a hairline shrinkage crack with no water, sure. The DIY kits from a big-box store run $50 to $100 and seal a clean dry crack reasonably well. Where homeowners get into trouble is on actively leaking cracks or cracks with horizontal movement. The injection ports do not bond to a wet concrete face, the resin gets diluted by the active water flow, and the crack stays open. Then we are out the next spring re-doing the job at the standard $400 to $600 price plus an hour of cleanup of the failed DIY ports.
Does either method need a permit in Dane County?
Crack injection on a non-structural crack does not need a permit. Crack injection paired with a structural fix (a wall anchor, a carbon-fiber strap, a partial wall rebuild) needs a permit pulled through the Dane County building inspector's office, and Wisconsin SPS 321 requires a structural inspection on any repair that changes the load path of a foundation wall. We pull that permit on every structural job we run. A standalone $500 polyurethane injection on a leaking cold joint is a straight repair, no permit required.
How long does the injected resin actually last?
Polyurethane lasts the life of the wall as long as the wall itself does not move. The resin is hydrophobic and chemically stable for decades, longer than any homeowner is going to keep the property. Epoxy is similar on the chemistry side, but it is rigid, so any future wall movement will crack the epoxy at the same spot. Polyurethane is flexible and will stretch with minor movement. That is one reason we lean polyurethane on Monona cold-joint cracks where the seasonal thermal cycle keeps the wall moving an eighth-inch back and forth.
Ready for a free inspection?
Call (608) 407-7510 and we will diagnose the crack and tell you which resin (or neither) is the right call. See the full Madison foundation cost guide for pricing across every service, the foundation crack repair service page for system detail, our Monona service area page for the cold-joint pattern we see most, and our companion piece on foundation repair cost in Madison for the full pricing context.
Last updated: 2026-05-01.