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Resin casting, ComposiMold vs. RTV Silicone molds

6 replies
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  • Member since
    May 2013
Resin casting, ComposiMold vs. RTV Silicone molds
Posted by R-4360 on Monday, September 2, 2013 4:02 PM

I've seen ComposiMold in FSM - anyone used it? Does it work as well aa RTV silicone molds?  Sounds great, reheat use over & over.

  • Member since
    November 2009
  • From: Twin Cities of Minnesota
Posted by Don Stauffer on Tuesday, September 3, 2013 8:24 AM

I have been wondering myself and looked at their web site. One thing that bothers me is that it doesn't take much temp to soften molds. I worry about resin temps during hardening softening mold.  That stuff gets reasonably hot if it is a good sized casting.  I am tempted to try the stuff but just haven't took the plunge yet. I have seen paper cups char when leftover epoxy set up in them.

Don Stauffer in Minnesota

  • Member since
    October 2009
Posted by hunter49 on Saturday, October 5, 2013 5:38 PM

I have recently tried it and I must say, that in my attempts to make a two part mold it was less than easy. The first pour was easy, just heat and pour. It's when the second pour was attempted it all went bad. It seems the stuff will stick to itself because it melts into the previous pour even with a recommended release spray. You must freeze the mold half before you pour the second hot pour. In my attempt it stuck together and I had to tear it apart losing the whole thing. I have tossed out the stuff in frustration.

  • Member since
    January 2006
  • From: California
Posted by SprueOne on Sunday, October 6, 2013 11:14 AM

Sorry to hear that.

Thanks for sharing that information.

I was thinking of trying the material but hadn't thought about that.

Anyone with a good car don't need to be justified - Hazel Motes


Iron Rails 2015 by Wayne Cassell Weekend Madness sprueone

  • Member since
    November 2009
  • From: Twin Cities of Minnesota
Posted by Don Stauffer on Sunday, October 6, 2013 11:19 AM

Sounds like it might only be of much use in a one-part (open) mold.  Ordinarily I used to avoid open molds, because the resin right next to the air never fully hardens properly.  However, I found a fix that helps a lot. I take a sheet of particle board, drill a "sprue" hole and vent hole in it, and use it to set on top of a one piece mold.  That way the actual surface of the part is not exposed to the air and sets properly.

I know resin is set thermally, not by evaporation of a solvent. I feel the problem with an open mold IS thermal.  The heat generated by the catalytic reaction seems to be dissipated in the air by convection around that surface.  Covering the mold with something seems to protect the part and only the tops of the pour and vent holes end up having the sticky surfaces, and those are cut off anyway.

Maybe I'll try some, with the restriction to use on single piece molds kept in mind, though.

Don Stauffer in Minnesota

  • Member since
    January 2010
Posted by CrashTestDummy on Wednesday, October 16, 2013 3:06 PM

For any two-piece (or more) mold, you'll need to coat the surface of the first mole half with mold release if you are going to expect any success.  The mold making compound, by it's nature, and you probably wouldn't want it to do anything otherwise, sticks to itself very well.  A couple of coats of mold release compound (works like a liquid wax) does the trick quite nicely.

Gene Beaird,

Pearland Texas

G. Beaird,

Pearland, Texas

  • Member since
    August 2012
Posted by JMorgan on Friday, February 28, 2020 5:08 AM

I just tried it and it's lousy. Easily melts styrene when trying to soften and clean it off. I'm also going to toss mine!


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