In short
Crack injection fills a crack in concrete with a resin under pressure. Epoxy can restore the bond across a dormant structural crack; flexible polyurethane can seal a leaking or moving one. It treats the crack, not its cause, so it works only after the cause, such as corrosion, overload or water, has been found and dealt with.
Key points
- Injection fills the crack along its depth, not just its surface.
- Rigid epoxy suits dormant cracks where bonding is needed; flexible resins suit leaks and movement.
- Injecting a crack caused by corroding reinforcement hides the problem without stopping it.
- A proper repair includes diagnosis, surface preparation, injection ports, sealing and a check afterwards.
Crack injection is one of the most effective concrete repairs, and one of the most misused. It is excellent at what it does and useless at what it doesn’t, so it starts with a diagnosis.
What injection does
A resin is pumped under pressure into a crack through small ports fixed along it, after the surface of the crack has been sealed. The resin travels through the depth of the element and fills the crack from inside, not just at the surface.
Two families of material
- Epoxy resins are rigid and strong. In a dormant crack, they can restore the bond between the two sides of the concrete.
- Polyurethane resins are flexible and some react with water. They suit cracks that leak or still move a little, where sealing matters more than strength.
The choice depends on why the crack formed, whether it moves, and whether water passes through it.
What injection does not do
Injection treats a crack; it does not remove its cause. If reinforcement inside the concrete is corroding, its rust expands and keeps cracking the concrete; injecting the crack hides the symptom while the damage continues. The same applies to cracks from overload or foundation movement. That is why Nation’s maintenance and rehabilitation work starts with diagnosis, often through a building safety report.
A proper repair, step by step
- Diagnose the cause and confirm the crack is suitable for injection.
- Prepare the surface and clean the crack.
- Fix ports along the crack and seal its surface.
- Inject from one end, port by port, until resin appears at the next.
- Remove ports and the surface seal once cured, and finish the surface.
- Check the result.
When something else is needed
Where cracks come from corrosion, the repair is to the concrete and reinforcement; see spalling concrete and corroding reinforcement. Where the structure needs more capacity, see structural strengthening.
Questions
Will the crack come back?
If the cause has been removed and the right material used, an injected crack should stay closed. If the cause continues, a new crack usually forms nearby.
Is injection the same as filling and painting?
No. Surface filling covers the opening; injection fills the crack through the depth of the element.