Why concrete cracks need more than a surface fill
A crack in concrete usually runs right through the section. Filling the surface closes the top few millimetres and leaves the rest open to water, which can reach the steel reinforcement, rust it and cause the concrete to spall. Resin injection fills the crack through its depth.
Two kinds of injection resin
Epoxy resin
- Bonds the two sides of a crack back together
- Very strong once cured
- For dry, non-moving cracks
- Used where strength needs restoring
Polyurethane resin
- Seals cracks against water
- Stays flexible after it cures
- Suits damp or leaking cracks
- Used where the goal is watertightness
Choosing the right one depends on whether the crack is moving, whether it’s wet, and whether the aim is strength or waterproofing. Structural cracks may need an engineer’s specification.
How resin injection works
- Assess the crack: width, depth, whether it’s moving and whether it’s wet.
- Clean the crack and fix injection ports along its length.
- Seal the surface of the crack between the ports so resin can’t escape.
- Inject under pressure, port by port, until resin shows at the next port along.
- Remove the ports and grind the surface flush once the resin has cured.
- Finish, including render repair and recoating on rendered concrete.
Where we use it
- Cracked concrete walls, including rendered concrete
- Retaining walls and boundary walls
- Cracks letting water into basements or under-croft areas
- Concrete elements under render that keep cracking through
When to call an engineer. Wide cracks, cracks that are growing, rust staining or spalling concrete can point to a structural problem. We’ll recommend an engineer’s assessment in those cases and can carry out injection to their specification.