Best material to add thickness for mold-making

I have a silly little project that I bet you folks can help me on,
if you will.

I want to mold a small metal object that is very very thin-- TOO
thin. So, what is the best material to paint on the back to thicken
it up a bit? Epoxy? Nail polish? Paint? It can be a rubber mold, or

I’d bet on epoxy, but why make your own mistakes when others have
already made them for you?



If it were me and I could use RTV materials, I would thicken the
piece with sheet wax. Easy to apply, easy to remove and just works

john dach

Noel, I have done just this using some old toys I had and I used the
UV resin. I was able to fill the entire piece since it had a depth of
only a centimeter and a half anyway. Hope this helps.

Hi Noel,

need some more info. What are you making the mould from? Is the back

If yes to this, acetate sheet would work well if using RTV silicon.


I’ve thickened thin pieces with one or more coats of epoxy gel on
the back.

It worked very well and has been durable. Also, easy and cheap!


I do this on a regular basis.

Use build-up wax with your wax pen. Its fast and easy and you can
build-up to whatever thickness you need.

Then of course you need to use a RTV mold compound. My favorite is
Castaldo Liquacast.

Carl Stanley

Sheet wax works good with RTV molds but for vulcanizing rubber molds
I use adhesive aluminum tape from hardware store. You can layer it
as needed and trim each layer with an Exacto knife as you go. Make
sure you burnish well each layer. At the end you can just peel it


I covered the back of a thin textured heart with paper clay, sold at
Michael’s/ A. C.Moore. Had cold mold made. Came out TOO thick! Also,
since they were contoured [undulating] some of the paper cracked off
but only AFTER the mold had been made.

While we’re at it I need to make the back of a sterling hand tooled
Infinity symbol thicker in one area. Paper clay would not work, so I
await solution. Anyone?

I've thickened thin pieces with one or more coats of epoxy gel on
the back. 

OK, if we can be sure epoxy does not interact in some negative way
with cold molding material, that would be good. The piece is a very
thin (.15mm in some spots) undulating dome shape (half a stepped
bead) so I need to be able to paint something on.


J. B. Weld sold at auto parts stores.

Can be sanded once hard and holds up under heat of vulcanization for
one mold.

Use like putty then shape when cured.

Another thing we do is nickel-plate at commercial plating company to
build-up total model.

Can be plated to increase mass to percentage desired to compensate
for moldshrinkage or just size desired.

Holds up for one vulcanization.

J B Weld been using it for 25 years or more…