When making a mold. if I use a 80g Emulsion Bound CSM as a sealer layer after Gel Coat which needs a polyester resin can I then use 300g Powder Bound CSM with Epoxy Resin for all the remaining layers of the mold? I realize that I can use polyester resin on the powder bound CSM but I would rather use Epoxy even though it is more expensive.

One of the reasons I would like to use epoxy resin is the plug I am building is made out of foam board from the local home depot and I have read that you can seal it with an epoxy resin and not a polyester resin. Does anyone know if this is true? I do know you can't do it with the polyester resin for a fact. I tried it and it ate the foam just like they said it would.

I guess that brings up another question.....Can you put CSM with polyester resin ontop of epoxy resin?

Thanks,

   Dennis G 

Hi Dennis,

if I use a 80g Emulsion Bound CSM as a sealer layer after Gel Coat which needs a polyester resin can I then use 300g Powder Bound CSM with Epoxy Resin for all the remaining layers of the mold?

I would not recommend backing up a polyester or vinylester gelcoat with epoxy resin. Although it will bond to some extent it won't be as good as polyester resin to back-up polyester gel or epoxy resin to back-up epoxy resin.

I realize that I can use polyester resin on the powder bound CSM but I would rather use Epoxy even though it is more expensive.

One of the reasons I would like to use epoxy resin is the plug I am building is made out of foam board from the local home depot and I have read that you can seal it with an epoxy resin and not a polyester resin.

I'm slightly confused by this. If your pattern is made of polystyrene then it's true that you can't 'seal' it with polyester or vinylester resin (or anything else that contains solvents) because they will dissolve the foam. Epoxy would be fine so you can coat the polystyrene foam pattern with epoxy and then flat and polish that ready to pull a mould off. Once you've done that, you would be OK to use either epoxy, polyester or cinylester gelcoat on that pattern as the gelcoat for your mould. Polyester resin will release of epoxy; it's epoxy that won't release off polyester (i.e. if the pattern was coated in polyester, which you've already found you can't do anyway because it will dissolve the foam) where you would have a problem.

From what you're describing you should start by coating the polystyrene foam pattern in epoxy (you might want to add a thin layer of glass as reinforcement too). Flat and polish until you've got the finish you want, then coat in release agent.

Then, you could either:

Use polyester gelcoat followed by polyester resin and emulsion bound chopped strand mat to make the mould.
or/
Use epoxy tooling gelcoat followed by powder bound chopped strand mat and epoxy resin to make the mould.

I hope this helps.

Matt Statham
Easy Composites / Carbon Mods - Technical Sales