Two different problems
A leaking crack in a basement wall and a structural crack in a beam can look similar, but they need different treatment. The first is a water problem. The second may be a strength problem. Identifying which one you are dealing with comes before choosing a resin.
Polyurethane injection: for active water
Polyurethane resins react with water and expand to fill the crack and seal the leak path. They are the usual choice for wet cracks, leaking construction joints, pipe penetrations and lift pits. Because the cured resin stays flexible, it can tolerate small movements that would crack a rigid repair.
Epoxy injection: for structural bonding
Epoxy resins are low-viscosity and cure rigid, bonding the two faces of a dry crack back together. They are used where the aim is to restore continuity in concrete, typically after an engineer has assessed the crack. Epoxy is not the right answer for a crack that is still moving or carrying water.
How the work is done
Both methods follow a similar sequence: map the crack, drill and fix injection packers at the correct angle and spacing, seal the surface where needed, and inject in stages until resin appears at the next port. Records of locations, resin used and results are part of a proper handover.
When injection is not enough
If water is entering through a failed membrane over a large area, injecting individual cracks will only move the leak. In those cases we recommend treating the source, and using injection as part of a wider repair.