PU injection vs membrane waterproofing
One stops active leaks from inside the structure; the other prevents water from entering at all. They solve different problems and often work together.
Petrashield Team
Editorial
Polyurethane (PU) injection and membrane waterproofing are often presented as competing options. They are not. They answer different questions: injection treats water that is already moving through the structure, while membranes stop water from reaching the structure in the first place.
PU injection works from the negative side, usually indoors, by pumping a resin into the crack or joint where water travels. The resin reacts with the water, expands, and seals the path. It shines on active leaks in basements, lift pits and joints where excavating or re-membraning the positive side is impractical.
Membrane systems, whether liquid-applied or sheet, work on the positive side: the surface the water hits first. A roof coating, a bathroom membrane under tiles, or a tanking layer on a retaining wall all belong to this family. Done correctly, the structure itself stays dry, which is always the healthier outcome for concrete and reinforcement.
In practice many projects combine both: injection to stop an active leak and stabilise conditions, then a membrane or crystalline treatment to give the structure durable protection. The sequence matters, and so does knowing when one method alone is enough.
If a contractor proposes injection for a problem that clearly needs positive-side protection, or a membrane over a crack that is actively flowing, that is a diagnosis problem, not a product problem.