Cracking and joint failure in resin floors
A straight line over a construction joint, a moving slab crack and a crack through a thick resin layer call for different repairs. Trace the crack through the assembly and understand movement before bridging it.
Read the crack pattern
| Pattern | Investigate | Implication |
|---|---|---|
| Straight line above a slab joint | Joint type, movement, whether film was carried across it | Movement detail may need reinstatement, not rigid filling |
| Irregular line through floor and substrate | Active slab movement, settlement, restraint or shrinkage | Concrete specialist may be needed before coating repair |
| Map cracking or checks in film only | Excess build, cure, thermal shock and chemistry | Review formulation and application records |
| Crack at edge, drain or change in build | Detailing, termination, thin spots and repeated wet/heat exposure | Redesign transition or local reinforcement where specified |
Why a coating cracks
Concrete expands, shrinks and moves at joints. A rigid, fully bonded coating can telegraph that movement. Some systems can accommodate limited movement, but capacity depends on the complete tested build, thickness, temperature and detail; it cannot be assumed from the resin family name. Over-thick or poorly cured films may crack within the coating itself. Traffic impact, thermal cycling, chemical attack and cleaning with hot water can add stress beyond the original brief.
Check whether the substrate crack is active by monitoring representative width and displacement over conditions relevant to the asset. If there is differential movement, water leakage or structural concern, seek an engineer’s assessment. A cosmetic skim coat is unlikely to remove a moving mechanism.
How to diagnose
- Map crack locations against drawings, slab joints, columns, drains, wheel paths and equipment bases.
- Record width and whether edges are displaced. Review dates and environmental or operating changes.
- Open a representative section to find whether the crack starts in the concrete, repair mortar or coating layer.
- Review original joint treatment, system thickness, mix/cure records and chemical/thermal service.
- Agree repair detail for each class of crack; verify with a trial in high-risk locations.
Repair choices and prevention
Remove unsound film, prepare sound margins and treat the concrete defect first. Static hairline cracking may permit an approved crack-repair detail. Active or designed movement joints need an appropriate movement joint assembly, flexible sealant and termination compatible with the coating system. Rigidly covering an active joint recreates the same line. Areas with thermal shock, frequent hot washdown or chemical exposure need a system selected for that service, including edge and drain details.
At design stage, map existing joints, specify whether each is maintained or treated, define exposure and acceptance criteria, and document the chosen ALKA build and cure. The commercial kitchen and carpark guides discuss demanding operating areas.
Common questions
Can epoxy bridge a concrete expansion joint?
A rigid coating should not simply be continued over a designed movement joint. Detail the joint for expected movement and the complete approved floor system.
Is every floor crack structural?
No. Film checking, shrinkage cracks and joint reflection differ. Displacement, growing width or damage to concrete should be assessed by a competent specialist.
Technical references and further reading
- ACI 515.3R-20: Assessment and Surface Preparation for Concrete Protection Systems
- Sika: Concrete surface preparation for resin flooring
- Sherwin-Williams: Preventing premature coating failure
- Additional technical reference
These references describe general mechanisms. ALKA’s current product TDS, approved build and the project’s measured conditions govern the actual repair.
Need a project-specific build?
Send the substrate condition, exposure, photos and programme to ALKA for a technical review of the complete system.
Planning guidance only. Confirm the current technically approved ALKA TDS/SDS, compatibility, testing and application limits before specifying or installing a system.