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Silicon Rubber Molds

Started by Carlo, June 25, 2018, 02:02:32 PM

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I thought some of the great minds and deep experience here might help me with a problem.

I am having trouble with the silicon rubber used for molds, and could use some advice. For years, I have been successfully using Smooth-On OOMOO-30 for molds. Problem is the short shelf life (6 mo.). I only use it now and then in small quantities, for my own parts. I hate to buy a whole new quart every time, to get the 2 ounces that I'll need at any given mold.  Any ideas or suggestions for other products?

Thanks,  Carlo


Used to use a industrial grade of silicone RTV that used a catalyst. Would measure out just what i needed and freeze the leftover RTV.

Bill Hudson
Bill Hudson
Fall down nine times,
get up ten.


Bob Uniack, an expert in that discipline, uses RTV silicone rubber and casting resin from Silpak, Inc. in Pomona, California. -- Russ

Bill Gill

This is probably a fringe response, but I have read about people making small molds out of "plastic" worms sold in bait shops for fishing - melting them in a pot on the stove and reportedly being able to remelt and reuse them several times. I have also heard of people using silicon caulk to make small molds - not pure silicon which has a limited shelf life, but silicon-acrylic combinations. The caulk was thinned with water to for the first several layers.

Lawton Maner

     Most of the "craft grade" molding compounds have a 6 month life from manufacturing to trashcan.  Depending on your needs you might be better off with small quantities of one of the "industrial" materials.

     I have successfully used the sink and shower silicon caulk to make small flat backed molds.  Since it is an adhesive. the pattern needs to be waxed before coating.  Petroleum jelly thinned with naphtha has worked for me for over 40 years.  I don't recall where I learned that trick.  Since it air cures, the caulk needs to be applied in thin (3-5mm thick layers) and left to cure overnight.  Since a squeeze tube is less then $ 7.00 cost isn't s problem for most of us.  When you finish with the mold, you can earn points with the local Goddess by re-caulking the seams in her kitchen back-splashes with the leftovers.


When I did this professionally I used these folks:

They sell quart kits of silicones. They were always very helpful too and I see their site now has loads of good how to info and videos.