Oomoo Silicone Molding Workflow?

Discussion in 'Replica Props' started by WShawn, Jul 9, 2015.

  1. WShawn

    WShawn New Member

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    I'm thinking about using silicone molding material for the first time, and I like to run my planned workflow past some of the experts on this forum.

    I want to make resin versions of the PKE meter shell halves I've built from an Iona shoe polisher. I think the resin will hold up better than my built-up polisher.

    I initially made molds from SharkThane Flex Pro 30-20 urethane casting rubber, a roughly 3/8" rubber blanket reinforced in plaster mother molds. Each shell half has an interior and exterior mold.

    Because I didn't want my masters to be damaged in any way I really slathered them with release agents, using both an airbrushed PVA coat and Pol-Ease 2300 silicone spray.

    I've done some test casts, and they're so-so. There are visible surface defects in the molds, not bubbles, but various bumps and rough spots. The casts could probably be cleaned up, but it would be swell to get a really nice mold and resulting casts.

    My plan would be to get the 2.8 pound trial kit of Smooth-On's Oomoo silicone rubber and use that to make new casts of the exteriors of my two mold shells, reusing my existing urethane molds for the interior molds. Surface defects inside the piece don't matter.

    I'd place my master shells back over their interior urethane mold halves, set the mother mold for the exterior halves in place, seal with clay, and mix and pour in the new silicone rubber.


    I want to use Oomoo because I can buy it in small batches and I should be able to get it locally at a Blick Art store. From what I've read Oomoo is subject to tearing. I really only need one good resin version of each half, and then maybe a few more for fun. Can Oomoo handle 5-6 resin casts given my setup with a mother mold and such?

    My shell masters are mostly styrene, Bondo, and filler putty, spray painted with Krylon primer. Do I need to spray a release agent onto my masters before covering them with Oomoo?

    If I need a release agent on my masters what should I use? My Polytek catalog from 1997 says silicone-based Pol-Ease 2300 may interfere with the cure of silicone mold materials. If that's the case do I need to clean off all residual Pol-Ease from my master and interior urethane mold parts? Alcohol?

    Will the Oomoo stick to my existing urethane rubber pieces?

    I think that's it for now. I feel it's better to try to include all of the details at once rather than dribble them in through the thread piecemeal.

    Thanks for reading.

    Shawn Marshalll
    Portland, OR

    PS: Here's another thread that elaborates on my construction of the PKE shells:


    Attached Files:

  2. robn1

    robn1 Master Member

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    Oomoo should be fine, it won't stick to the urethane mold or the master. I'm not familiar with Pol-Ease, but if it contains silicone it should be cleaned off the master.

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