Hey.

I read that you could not use polyester gelcoat into molds to make best use of epoxy, but that you should use vinylester gelcoat.

Is that correct?

Why? 

Magnus

Hi Magnus,

You could spray them with PU and then re-finish that surface (the paint will be orange-peel like and will need flatting and polishing) and that would make them much likely to release epoxy parts if using a chemical release agent but not only would the PU paint finish require quite a bit of work (all the flatting and polishing on the *inside* of a mould, which is always the more difficult face to work on) but PU paint is also no where near as tough and durable as a mould finish as a tooling gel coat and so if you're taking multiple releases out of these moulds then I'd certainly prefer to have a gel coat finish than a paint finish. Paint is fine for going from a pattern to a mould or from a mould for a very short production run but as your day-to-day mould finish I don't think it would be a good move.

My suggestion would be to try a small area of your mould first with epoxy. If the moulds are old and have already release many parts then it might not be such a problem to release epoxy out of them (there are members on this forum who manage to do just that). The important thing is to expect the worst when releasing epoxy out of polyester and so test thoroughly and prepare accordingly.

--Matt

Matt Statham
Easy Composites / Carbon Mods - Technical Sales