Choose between epoxy and polyurethane resin for foundation crack injection

Steps

1. Diagnose whether the crack is actively leaking (wet/weeping) or dry: polyurethane is the default for actively leaking cracks because it's hydrophilic and reacts with the water present to expand and seal, while epoxy generally needs a dry substrate and loses adhesion when applied wet.
2. Confirm whether structural repair is a goal: epoxy cures rigid with high compressive/tensile strength and is appropriate for structurally bonding crack faces (when the movement causing the crack is resolved/non-progressive); polyurethane cures flexible and is not a structural adhesive in the same sense.
3. Assess ongoing crack movement: flexible polyurethane can accommodate minor seasonal thermal/moisture movement without re-cracking, while a rigid epoxy repair can crack again adjacent to the original repair if movement continues.
4. Confirm the underlying cause (settlement, hydrostatic pressure, drainage defect) has been or will be addressed — injection seals the crack but doesn't fix a root structural or drainage cause.
5. Follow the resin manufacturer's injection-port spacing and pressure instructions to ensure full-depth crack penetration — low-pressure or under-spaced ports are a common cause of a repair that doesn't actually stop the leak.