What is crack injection and when should it be used?

Crack injection is the process of filling cracks in concrete by pumping a liquid resin or grout into them under pressure, restoring watertightness and — with the right material — structural continuity. There are two main approaches. Polyurethane (PU) injection uses a resin that reacts with water and foams to fill the crack, making it the standard choice for sealing leaking cracks in basements, tunnels and retaining walls; it remains slightly flexible, so it tolerates minor movement. Epoxy injection uses a rigid, high-strength resin that bonds the two faces of the crack back together, effectively welding the concrete — the right choice where the crack affects structural capacity and the cause of cracking has been resolved. Crack injection is appropriate for cracks from around 0.1mm up to several millimetres wide, and is carried out from one side, which makes it ideal for structures where excavation is impossible. It is not the right repair for cracks that are still moving seasonally (these need a flexible sealed joint instead) or where corrosion of the reinforcement caused the cracking — that requires breaking out and structural repair. Typical UK costs run from £150 to £400 per metre of crack injected, depending on access, crack width and resin type.