PU injection stops water coming through cracks and joints in concrete by filling them from the inside with a resin that expands on contact with water. It is used in basements, lift pits, tanks and retaining walls, and it works while the leak is active, without digging around the outside or breaking out the structure.
Where it is used
- Basement walls and floors with water running through a crack or a construction joint.
- Lift pits that keep filling with water.
- Water tanks cracked from shrinkage or movement.
- Retaining walls and podium slabs with leaking joints.
- Pipe penetrations through concrete walls where water tracks around the pipe.
The common thread is concrete below or against water, where the outside face cannot be reached.
How injection works
- Survey the crack. Width, length, depth and whether it is wet or dry decide the resin and the spacing of the injection points.
- Drill and fit ports. Holes are drilled at an angle to meet the crack inside the concrete, and injection ports (packers) are fitted along its length.
- Inject. Resin is pumped through each port under pressure until it fills the crack and appears at the next port.
- React and seal. Water-reactive PU foams and expands in the crack, sealing it from the inside.
- Finish. Ports are removed, holes are sealed and the area is checked for water.
PU or epoxy?
- PU (polyurethane): flexible and water-reactive. Used to stop leaks, including active ones, and in cracks or joints that move slightly.
- Epoxy: rigid and very strong. Used to bond dry structural cracks back together. It does not suit wet, actively leaking cracks.
Many jobs use both: PU where water comes through, epoxy where a dry crack needs strength. A structural crack should also be checked by an engineer.
When injection is not enough
Injection seals defined cracks and joints. If damp comes through the whole wall, if white salt deposits cover large areas, or if groundwater pressure is high across the slab, a full basement waterproofing system is needed, often with injection at the joints as part of it. Surface patches and paint on the inside face do not hold against water pressure.
Signs you need it
- Water running or dripping through a visible crack or joint.
- A lift pit with standing water after every rain or high groundwater period.
- Rust staining around a crack, which means water is reaching the reinforcement.
- Surface repairs over the crack that keep failing.
What to expect on the day
Most injection jobs take a day or less per area, depending on the length of the cracks and the access. The area stays usable afterwards, and there is no excavation. We check the repair under water pressure before handover, and if it leaks again, we come back.
See crack injection and grouting for the full scope. Send photos or a short video of the crack and the water coming through on WhatsApp, and we will tell you whether injection is the right fix.