Polyester resin mold - how to release?

edited December 2016 in Fabrication
I want to make a hard and light weight mold with polyester resin and fiberglass, and cast platinum silicone in this mold.
But before i made many tests with different releasers and silicones, but there is a problem - when silicone cured, all surface (which contact with polyester resin) is slimy. 
I saw how used polyester mud, or bondo-resin mix in your lessons to making molds, but i cant release those materials... (

p.s.: i attached photo of my character which i want cast in fiberglass mold, but because of my problem i cast it in silicone mold. 


  • Hi Anton,

    You should be able to cast silicone into a fiberglass mold without any release agent, as silicone does not like to stick to anything other than silicone.

  • thanks for answer, @Chris Ellerby , but problem is that silicone, which touches the polyester resin does not cure (bad chemical reaction). maybe its about polyester resin that i'm using, and even after painting the mold with primer and acrylic lacquer, cured silicone is slippery.

    what do you think?



  • Platinum silicones can apparently have inhibition issues with freshly cast polyester molds, but I've not encountered that personally.

    Smooth-On suggests coating the polyester mold in a clear acrylic lacquer.  I often use Krylon's crystal clear.  It should provide a good barrier to prevent inhibition.

  • thanks again, @Chris Ellerby

    i will continue to search for solutions

  • What is the original sculpture made from Anton?
  • hi, @Peter Tindall
    original sculpture of the head was sculpted with ordinary plasticine, and tentacle - with nsp chavant.

    some photos:

  • Hmm when you had the issues with inhibited silicone was it the whole thing or just the main body?
  • @Peter Tindall
    Octopus on the photo was casted in silicone mold.

    The problem with polyester mold was on the whole surface of silicone
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