Short answer
Build-up is the non-volatile fraction of the release agent plus PU dust and flash. Over-application speeds it up. It dulls the surface, blurs texture and later causes sticking and paint defects. Spray thin and even, and clean on a cycle-count schedule with a cleaner suited to the mould material. Epoxy moulds can be attacked by aggressive solvents.
Likely causes
Over-spraying
More film than the part needs, building up with every cycle.
Mould too cool for the agent
Incomplete flash-off leaves residue.
PU flash in vents and parting lines
Cured material accumulates at edges.
Mixing release products
Incompatible agents leave tacky layers.
How to diagnose it
- Inspect vents and edges first.
- Compare gloss and texture detail against a freshly cleaned area.
How to fix it
- Reduce film weight and check atomisation.
- Clean with a grade made for your mould material: metal or epoxy.
- Never scrape epoxy moulds with metal tools.
- Ensure no cleaner residue remains before spraying release agent.
How to stop it coming back
- Set cleaning intervals by cycle count.
- One release system per mould.
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.
