Basements & Substructure
Crack Injection Failures
Crack injection — using epoxy resin or polyurethane foam — is the primary repair method for water-bearing cracks in basement concrete walls and slabs. When correctly executed, injection creates a watertight seal within the crack. When it fails, water reappears at the same crack or at adjacent locations as the water finds new paths. Injection failures arise from incorrect product selection, insufficient injection pressure, active water in the crack washing out the resin before cure, or structural movement reopening the crack after injection. Understanding the failure mode is essential to selecting the correct re-injection or alternative approach.
Common Signs
- Water reappearing at a previously injected crack location
- Injection ports still visible from a previous repair
- Hollow sound when the injected crack zone is tapped — indicating incomplete fill
- Water appearing adjacent to the injected zone — indicating the crack has propagated
- Damp staining or efflorescence at injection port locations
- Cracking visible in the hardened epoxy at the crack face
- Failed polyurethane foam visible at the surface — compressed or washed out
Common Causes
- Epoxy injected into an active (still wet) crack — water washes resin from the crack before cure
- Injection pressure insufficient to fill the full depth and width of the crack
- Crack still actively moving after injection — reopens the sealed zone
- Wrong product selected — low-viscosity epoxy for a wide crack does not fill the crack profile
- Ports spaced too far apart — crack not fully saturated with resin
- Crack faces contaminated with oil, release agent or old sealant preventing resin adhesion
- Polyurethane foam over-expanded and pushed out of the crack rather than consolidating within it
Risk of Neglect
- Ongoing water ingress at failed injection locations causing building damage
- Water finding new pathways through adjacent cracks and construction joints
- Ongoing corrosion of basement reinforcement from chronic moisture
- Increasing cost of re-repair with each failed injection cycle
- Structural capacity concern where cracks are in load-bearing basement walls
- Owner corporation frustration from recurrent failed repairs without root cause resolution
- Escalation to more invasive and expensive cavity drain or external waterproofing solutions
Inspection Requirements
Download Inspection Checklist- Inspect all previously injected cracks for recurrence of moisture, staining and efflorescence.
- Tap the injected zone to assess whether the resin has fully consolidated within the crack.
- Check whether cracks are still active by installing tell-tales before committing to re-injection.
- Assess the crack width and depth — measure at the face and probe depth where possible.
- Confirm whether water is active (flowing) or passive (seeping) in the crack — different products apply to each.
- Review previous injection contractor records to determine the product used and ports spaced.
- Engage a specialist waterproofing engineer to confirm the re-injection specification and product selection.
- Assess whether the structural cause of cracking has been addressed — re-injection without structural stabilisation will fail again.
Start Inspection Checklist
Create a project inspection record, add defect locations, upload photos, and save notes for scope writing.
Typical Repair Methodology
- 01.Confirm the crack is dormant or arrest active movement before re-injection.
- 02.Remove all previous injection ports and resin residue from the crack face.
- 03.Clean the crack face with high-pressure air to remove all contamination.
- 04.For active wet cracks — use a hydrophilic polyurethane resin that reacts with and expands in the presence of water.
- 05.For dormant dry cracks — use a low-viscosity epoxy resin to structurally rebond the crack faces.
- 06.Space injection ports at maximum 100 mm centres for fine cracks, 150 mm for wider cracks.
- 07.Inject from the lowest port upward, moving to the next port only when resin appears at the adjacent port.
- 08.Maintain injection pressure until the resin has fully saturated the crack before capping the port.
- 09.Allow the resin to cure for the full manufacturer-specified time before water testing the repair.
- 10.Apply a crystalline waterproofing coating to the repaired zone as a secondary measure.
- 11.Monitor the repaired crack over 4 weeks before confirming success.
Related Repair Systems
- Polyurethane hydrophilic injection systems
- Epoxy resin structural crack injection systems
- Crystalline waterproofing coating systems
- Crack monitoring and tell-tale systems
- Waterproofing engineer assessment services
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