epoxy polyester issue

[brokensheer]

Hello i am having a bit of a time building a small mold, the two attempts using a NON styrene compatable foam plug failed, even with the new sealers,, so I have coated the foam in epoxy, my question is can I build bulk over the epoxyand glass with polyester this is a small part 16" x 24" once I get a good pull from it I can make a few poly molds,,

Your thoughts?

[BATAAN]

The only problem with epoxy is that polyester won't stick to it well.
Using mold release as usual should work fine if you are forming polyester part over epoxy form.
In the past in movie special effects, we have used polyurethane foam to sculpt 'things' (monsters, etc), faired and finished with quick sheet rock mud (it sands about the same as the foam), then apply PVA release, then glass with polyester and cloth to make a mold.

[brokensheer]

That is kind of where I failed this part is a femal U shape and when I sprayed the styrene blocker O lost the size of the part, What I am trying to do , is have the epoxy be the finished mold surface and the poly be under that to build bulk

Thanks

[BATAAN]

Epoxy will sort of stick to poly if you sand it well. Good enough for a mold but not good enough to build parts of. So your example is a female u-shape and the mold is reverse and you are making the part of polyester?
Here are some places for you to look for answers.
http://www.rcgroups.com/forums/showthread.php?t=793671
This is from a guy who does a lot of molding with the materials.
More:
http://www.westsystem.com/ss/problem-solving/
http://www.epoxyworks.com/22/polyester.html
http://en.wikipedia.org/wiki/Epoxy
http://www.rcgroups.com/forums/showthread.php?t=1394074

[brokensheer]

Thanks!

[tunnels]

You cant and should not try to mix resins systems . epoxy is epoxy and the top of the pile polyester is the bottom of the pile vinylster is the middle . poly and vinyl are compatable 95 % of the time but epoxy is the odd one out !! Making moulds use pvc foams not polystyrene . what you start with you should carry on with . simple !! yes you can do some mix and match but have to know what you are doing . KEEP IT SIMPLE !!