1. Hez is offline
    Member Since
    Dec 1999
    Dec 17, 2008, 10:53 PM - Silicone shrinkage issues? #1

    Hoping someone can help with this, I used some por-a-mold thixatropic from Dick Blick to mold a helmet, and had a couple of issues with it. Firstly, it took ages to cure in a couple of spots on the inside of the mold, it was tacky for a while. Secondly, now that I've started pulling casts from it, they have what I would estimate to be around a 4% shrinkage on them.

    Is this normal for this silicone, or did I get a bad batch? As it is I'm considering just tossing the mold and starting again with something else anyway, any recommendations?
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  3. exoray's Avatar
    Member Since
    May 2003
    Dec 17, 2008, 11:01 PM - Re: Silicone shrinkage issues? #2

    I'm almost certain that that is a polyurethane rubber not silicone...

    So yes shrinkage like that is probably happening, you won't be able to measure the shrinkage with silicone in most cases...

    Confirmed that Sil-Mold line is their silicone rubber, the Por-A-Mold line is polyurethane...
    Last edited by exoray; Dec 17, 2008 at 11:04 PM.
  4. Hez is offline
    Member Since
    Dec 1999
    Dec 17, 2008, 11:12 PM - Re: Silicone shrinkage issues? #3 was listed along with the silicones on Blicks site. I guess that's what I get for assuming. Mind, I just checked and Blicks never states that it isn't a silicone either.
  5. ArtisanProps's Avatar
    Member Since
    Nov 2006
    S. Florida
    Dec 18, 2008, 1:08 PM - Re: Silicone shrinkage issues? #4

    Yes, and if you want the least amount of shrinkage (insert joke )
    Go with a Platnium Cured Silicone, the shrinkage is negligible unless otherwise
    stated in the tech bulletin..........
  6. Tim Allen's Avatar
    Member Since
    Dec 2005
    Southern Cali (Orange County)
    Dec 18, 2008, 1:16 PM - Re: Silicone shrinkage issues? #5

    Ive been using this silicone from smooth on called Rebound 25, really easy to work with A+B and added a thixotropic to it didnt have any weird effects with the curing or shrinkage. If their was any shrinkage I sure couldnt tell to the human eye

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