Epoxy vs. Polyurethane Crack Injection
Two resins, one crack. Pick the wrong one and you either get a wall that still leaks, or a repair that cracks again beside the old one. Here's how to tell which one your crack needs.
Epoxy vs polyurethanePage 05
Is polyurethane or epoxy better for crack injection? Polyurethane is better for leaking foundation cracks. It expands into a flexible foam that blocks water, even in a wet crack. Epoxy is better for dry cracks that have stopped moving, because it cures hard and bonds the concrete back together. Most basement leak repairs use polyurethane.
Below: how each resin works, a side-by-side table, what each one can't do, and what DIY kits are good for. The full repair process is on our crack injection page.
How does polyurethane crack injection work?
Polyurethane goes into the crack as a liquid. When it meets water, it reacts and expands into foam that fills the crack all the way to the soil side of the wall.
Because it stays flexible, it can move a little when the wall moves with the seasons. That's why it suits basement leaks: the job is to keep water out, not to hold the wall together. How we do it: polyurethane crack injection.
Think of it like expanding foam around a window frame. It seals the gap. It doesn't make the frame stronger.
How does epoxy crack injection work?
Epoxy goes in as a thin liquid and cures into a hard solid. It glues the two faces of the crack back together. A properly injected crack can end up as strong as the concrete around it.
The catch: epoxy is rigid. If the wall is still moving, a new crack can open right beside the old one. Epoxy also bonds best to a dry crack, so it's a poor choice while water is coming through. How we do it: epoxy crack injection.
Epoxy vs. polyurethane side by side
| Polyurethane | Epoxy | |
|---|---|---|
| Main job | Stop water | Bond the crack back together |
| Once cured | Flexible foam | Hard solid |
| Wet or leaking crack | Works, moisture helps it react | Works best dry |
| Wall still moving a little | Flexes with it | Can crack again beside the repair |
| Typical use | Most basement leak repairs | Dry cracks that need strength, after the cause is fixed |
What can't either resin do?
Neither one fixes the reason a wall cracked in the first place.
- A horizontal crack or a bowing wall usually means soil is pushing the wall in. Resin can seal the leak, but a structural engineer should decide how to stop the movement.
- Concrete block walls are hollow, so resin runs into the cores instead of filling the crack. Block walls are usually sealed a different way.
- A crack that keeps getting wider needs its cause found before anything gets injected.
Are DIY injection kits any good?
Kits sold at hardware stores use the same two resins. They can work on a thin, dry crack in a poured concrete wall.
They're much harder to get right on an actively leaking crack. The resin has to reach the soil side of the wall, and you only find out it didn't when the next heavy rain comes. If water is already coming in, a professional injection is the safer bet.
Which one do we use?
We decide after we see the crack: whether it leaks, whether it's moving, and what the wall is made of.