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  1. Member Since
    Dec 1999
    Messages
    1,309
    Dec 17, 2008, 11:53 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?
  2. exoray's Avatar
    Member Since
    May 2003
    Messages
    5,852
    Dec 18, 2008, 12:01 AM - 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 18, 2008 at 12:04 AM.
  3. Member Since
    Dec 1999
    Messages
    1,309
    Dec 18, 2008, 12:12 AM - Re: Silicone shrinkage issues? #3

    Dangit...it 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.
  4. ArtisanProps's Avatar
    Member Since
    Nov 2006
    From
    S. Florida
    Messages
    551
    Dec 18, 2008, 2:08 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..........
  5. Tim Allen's Avatar
    Member Since
    Dec 2005
    From
    Southern Cali (Orange County)
    Messages
    591
    Dec 18, 2008, 2:16 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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