Active vs Passive Leak Injection in Concrete Structures

When a basement wall, tunnel liner, or water-retaining structure starts to leak, the first technical decision is whether the leak is active or passive. The classification drives every subsequent choice: resin type, packer placement, injection pressure, and follow-up structural repair.

Active vs passive — definitions

An active leak is one with visible water ingress at the time of inspection. A passive leak is a crack or cold joint that is currently dry but is likely to leak under future hydrostatic pressure, rainfall, or seasonal groundwater. The same crack can move between states.

Side-by-side comparison

Methodology

For an active leak, hydrophobic polyurethane foam is most commonly used: it reacts with water to expand 20–40 times, displacing water and forming a flexible closed-cell foam that seals the crack. Once the leak is stopped, a permanent epoxy or curtain injection can be performed for structural restoration if required. For a passive structural crack, low-viscosity epoxy is injected under pressure to fully wet the crack faces and restore monolithic behaviour to the concrete.

• Mark crack, install mechanical packers along its length (typically 150–300 mm spacing).
• Clean surface and seal between packers with paste.
• Inject resin from the lowest packer upwards (active) or from one end to the other (passive).
• Confirm flow at the next packer before moving on.
• Remove packers and grind the surface flush after cure.