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RTV Molding - parting agent


Hi: I am going to be making some RTV rubber separation molds and I am
looking for the best parting agent to use to prevent the halves from
sticking together. Will a silicone mold release be effective? Is talc
required and if so, how much? I will appreciate any data sent, thanks
in advance



Lee, You didn’t say which RTV you would be using but since most RTV’s
I have worked with are self releasing you shouldn’t have a problem.
Make the mold in two steps, letting the first half cure before you
pour the second half. Personaly I prefer to cut my molds the same as
you would a vulcanized mold. If you need any more info on RTV brands I
suggest you check out the archives. Good luck Frank


Hi Lee, Silicone spray will prevent RTV curing in some cases. Some
people use a spray furniture wax like J&J. A furniture spray is
usually water based and takes a while to dry. My favorite is called
Synlube. It is a parafin wax in a solvent base. Use mega ventilation
or do it outside. It is from Synair corp. Ask for Synlube 531 Release
Agent. They also make a nice line of RTV products which are very
affordable. Be sure to ask for their brochures and of course the MSDS
forms. They can be reached at 1-800-897-3454. J.A.


Lee, I like teflon over just about anything. It can be obtained at
your local hardware store in spray can form. GUNK is one, just look
at the contents and make usre it contains teflon. There are companies
who make an sell parting agents (Miller-Stephens for one) and they
have great teflon coatings. Silicon is ok, so is vasoline, vasoline
in a solvent (doesn’t make quite the mess and is easy to apply, soap
(if you get a very good coat), etc. Talc is ok in some types of
vulcanized rubbers, but I usually cut them. Most mold rubber
mfgrs/resellers have one or more releases available for different
types of RTV’s.

John Dach

MidLife Crisis Enterprises
C.T. Designs
Cynthias sculptures are at:


Dear Lee,

I don’t think any of the parting agents normally used will work with
an RTV mold because the liquid will wash away the film layer a
separation mold depends on. One way to do it is to pour and cure 1/2
of the mold, then apply the parting agent, and then pour and cure the
other half. This take a relatively long time – two cure cycles-- but
it will work. The parting agent you use depends on the RTV rubber you
choose. Silicone sprays should not be used with RTV silicones because
they can act as bonding agents - -the wrong idea entirely! We
(CASTALDO) make an non-silicone RTV called LiquaCast that is cheaper,
stronger, longer lasting and easier to work with The separation
agent for this compound is any kind of wax - Pledge furniture polish,
or any other kind of spray wax.

If you (or any one else out there) would like a free sample of
LiquaCast, please let me know and please give me your shipping address
(no P. O. boxes, please).

        Michael Knight


I have had very good results using polyvinyl alcohol as a parting
agent for RTV molds. Just paint it lightly on to the original and
release is easy. MP