epoxy polyester issue

Discussion in 'Fiberglass and Composite Boat Building' started by brokensheer, Jan 9, 2012.

  1. brokensheer
    Joined: Jun 2009
    Posts: 201
    Likes: 3, Points: 18, Legacy Rep: 14
    Location: So. Md

    brokensheer Senior Member

    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?
     
  2. BATAAN
    Joined: Apr 2010
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    Location: USA

    BATAAN Senior Member

    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.
     
  3. brokensheer
    Joined: Jun 2009
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    Location: So. Md

    brokensheer Senior Member

    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
     
  4. BATAAN
    Joined: Apr 2010
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    Location: USA

    BATAAN Senior Member

    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
     
  5. brokensheer
    Joined: Jun 2009
    Posts: 201
    Likes: 3, Points: 18, Legacy Rep: 14
    Location: So. Md

    brokensheer Senior Member

    Thanks!
     

  6. tunnels

    tunnels Previous Member

    :pYou 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 !!:confused::eek::D:p
     
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