Short answer
Adhesion fails when something stands between the coating and the PU. The usual culprits are release agent that is excessive or not coating-compatible, a coating film poured too early (still wet) or too late (fully dried), wrong mould temperature, silicone contamination, or a coating not matched to the PU. Validate the pairing of release agent, coating and PU first.
Likely causes
Release agent not IMC-compatible, or too much of it
Acts as a parting layer under the coating.
Pouring too early
Solvent or water trapped under the film.
Pouring too late
Film fully dried and no longer bonds.
Film too thick
Cohesive failure inside the coating.
Silicone contamination
From sprays, gloves or neighbouring processes.
Chemistry mismatch
Coating not designed for your PU hardness or system.
How to diagnose it
- Does it peel at edges only or everywhere?
- Measure the time between spraying and pouring.
- Re-test with a fresh release coat and a clean mould.
- Cross-hatch adhesion test on a sample part.
How to fix it
- Use a release agent grade designed for in-mould coating.
- Apply thin, even coats of both release agent and coating.
- Set the spray-to-pour window and mould temperature by trial.
How to stop it coming back
- Validate the release agent + coating + PU set together.
- Write the spray-to-pour window into the work instruction.
Where this problem appears most
Send us your batch number, PU system and a photo of the defect and our technical team will help you trace the cause. Ask a technical question.
