Making a 100% Silicone Caulk Mold

Silicone Caulk Experiments
Silicone Caulk Experiments!

(Edit: See also 100% Silicone Caulk Molds — Round 2, Fight!)

I’ve been so wrapped up in trying to learn how to paint Live Show Quality horses that I’ve drifted away from the goofier side of things. But since I declared May was going to be my FAFFing month, I figured I’d try something new… 100% Silicone Caulk mold making! 😀

I love painting and I love sculpting, but I get paralyzed when I only have one copy of something to paint (or modify). Thus I’ve always wanted to be able to create my own castings to paint.

But silicone molds and resin aren’t cheap– and I am. *clings tightly to her pennies*

Thankfully the Internet Hivemind is a thing and I started stumbling across pinterest pins, youtube videos, DIY articles, and how-to’s on making molds from bathroom caulk, so I decided to give it a go.

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Failure #1 : Cornstarch and Caulk

Caulk Cornstarch Fail
Caulk Cornstarch Fail

Since this was the first method I came across, it was the first one I tried. With horrible, horrible results. *sighs*

(2016 Update: I tried again and this time it worked!)

In this, there is no water involved at all– just caulk and cornstarch (and sometimes acrylic paint). You squeeze out the caulk onto a smooth surface and then use a stiff card to fold in the cornstarch until it’s well mixed.

You’ll want to coat your hands in something protective before you use them as the caulk is VERY sticky to start with. I just cheated and waited until the mixture was not tacky before I started hand-working.

Once the caulk is no longer sticky and feels about like clay, you can use it to mold the object.

It looked and felt fine when I was working with it, but it only partially cured leaving me with a crumbly mold that stuck to my poor sculpey master. I even gave it 12 hours to dry, which was a heck of a lot longer than most of the videos suggested.

Thankfully the sticky bits scrubbed off without issue, but it wasn’t the best start to the experimentation. Still, lots of folks on YouTube have had great success with it, so I’ll have to try again sometime to figure out what I was doing wrong. (click to enlarge photos)

Failure #2/Win #1 : Soap, Water, Caulk, and BUBBLES FROM HECK!

Silicon and Sopy Water Mold
Silicon and Sopy Water Mold

Since the cornstarch didn’t work, I went back to the web to find out what I was doing wrong… and found a bunch of alternate methods instead.

I work inside (with open windows and large box fans), so I didn’t want to involve paint thinner or any of the more toxic mixtures. Although a pourable mold material looked awesome, I went with the next best thing, a giant bucket of soapy water!

This turned out to be the method I ultimately used, once I got the technique down well enough to get rid of the bubbles.

(And there were a LOT of bubbles.)

Bucket of Soapy Water
Bucket of Soapy Water

Required Materials

  • Bucket
  • Water
  • Lots of Cheap Dish Soap
  • 100% Silicon Caulk
  • Something to mold
  • Hands

Fill the bucket with water at least eight inches deep or so, you want plenty of room to work with the caulk underwater.

Add dish soap until your hand feel slimy. There is no set method for this, but the soap keeps your the caulk from sticking to your hands and acts as the catalyzing agent, so don’t be skimpy. (Although you can reuse the water for several days.)

Stick the nozzle of the caulk gun into the water and carefully squeeze out the caulk, catching it and keeping it under the water with your free hand.

I was able to make the mold with only two or three trigger pulls of the caulk gun, but experiment! It’s only $5, so it’s not like the learning curve will kill you. I spent my first tube figuring things out and now I’m on my second and feeling pretty good. 🙂

First Mold Lots of Bubbles
First Mold Lots of Bubbles

Once you have enough caulk squeezed out, use both hands to flatten out the caulk so the soap can interact with it. Just flatten and fold, flatten and fold. When I did a more rolling, ball-making motion I ended up with a lot more bubbles, but try whatever technique you like to find your own happy place.

The purple on the mold is just a bit of a paint wash to highlight how bad it was. (I seriously just need to throw this mold out, but I’m too attached).

The silicone will firm up a bit in your hand after only a few minutes, so once it starts feeling like clay and less like toothpaste, pull it out.

Dunk the object you will be molding in the soapy water as well. Silicone doesn’t really need a release agent, but it never hurts to be careful.

Sculpey Mother Mold
Sculpey Mother Mold

There are two ways of making the mold, either press the silicone down onto the object (which is what I did above) or press the object down into the silicone (which is what I did for the second mold).

If you press the silicone down onto the object, make sure to make the back flat (like I didn’t) or you’ll need to make a mother mold out of clay or plaster later, so that it sits flat when you flip it over.

I made the clay mold above when trying to use it as a press-mold because it deformed under the pressure. Then I made a plaster of paris mother mold (another post on that later) so it was nice and level for the plaster cast pours.

Press Mold Sculpey
Press Mold Sculpey

Make sure the back of the mold is thick enough so the items doesn’t go all the way through. I made mine anywhere from a quarter to a half-inch thick and it set up just fine. I also had a few that got really thin in places, but thankfully I haven’t had them rip yet!

Now walk away… for about two hours.

(This really is the hard part, I kept coming back and poking at it.)

Check to see if the caulk is done by poking it with a finger. It shouldn’t be sticky at all and feel nice and hard. If it gives, or if you can poke it with a finger and leave a depression, it’s not set.

If it still hasn’t set after two hours, you can try adding soapy water to the container that holds the mold, I’ve had some luck de-sticky-ing molds this way– they were the ones that I didn’t work long enough under water to start with.

Plaster Casting Victory!

Plaster Cast and Second Mold
Plaster Cast and Second Mold

I’ve gotten to the point where I only give the molds a few hours of drying time (after demolding) to start pouring in the Plaster of Paris, but you might want to give it a bit longer. I’m still learning how to cast things, so I’m not as concerned for how long the molds will last.

I’ve done some sculpey push molding, some Hot Glue (High Temp), but am focusing mainly on doing plaster casts.

A) It’s cheap ($5 for a four pound bucket)
B) It’s fun to do ‘clay-body customs’ while the plaster is still a little wet (right after demolding)
C) Resin is crazy expensive
D) I can also make mother molds and normal molds out of it
E) Resin is crazy expensive 😉

And lo… thus endeth my sort-of-a-tutorial on Silicone Caulk Mold making! If you have any questions, just drop me a line below. I’ll be doing other posts on making the mother molds, hot glue and plaster casting, and whatnot.

And someday, maybe resin. …. Maybe. *eyes her penny horde*

Martha Bechtel

My name is Martha Bechtel and I write fantasy and science fiction stories, paint small model horses silly colors, cast resin and plaster magnets, code random code (and Wordpress plugins)... Come on in and join in the fun!

This Post Has 2 Comments

  1. Cathy

    Hey, really nice tutorial. I have been trying to make molds for a while now and the silicone caulk didint work for me eaither. I bought some liquid silicone but it turned out to be to expensive and tedious. Do you think I could make a two faced mold for plaster with the caulk and water example? thankyou 😀

    1. Martha Bechtel

      I haven’t tried a two-part mold, but if you are willing to wait until this weekend I can do a test run for you! 🙂

      How complicated of a mold are you trying to make? Most of mine are pretty simple, but I can try and cast something more complex if you’d like.

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