Monday, April 2, 2018

Molding Monday - Making a Rubber Mold

The rubber mold-making materials arrived from Micro-Mark and - as has been the typical story with this project - they sat in the unopened box for a few weeks. But this weekend I got a block of time to get them out and make my first rubber mold!

The photo above shows where I'd left off: master hot glued to a foamcore base and foamcore walls hot glued together to make a box (make sure all of the joints are sealed - you don't want any material leaking out).

First thing I did was get out the instructional video and watch it again. The process Dave Frary describes is pretty straightforward:
  • Make sure the mold box is level in all directions
  • Use rubber gloves
  • Apply mold release to the master and the inside of the box. Wait to dry.
  • Pour rubber mold material Part A into one cup and an equal portion of Part B in another cup
  • Mix together in a larger, clear cup (so you can see that it's mixed thoroughly)
  • Mix gently to reduce the number of bubbles
  • Let the mixture sit to allow as many bubbles as possible to come to the surface (this material has a 10 minute work time from mix to pour)
  • Pour the rubber into the mold from high up (12" +/-) so you have a small, thin stream (again, to reduce bubbles), starting in one corner and covering the entire master.

Straightforward in description. Execution was a wee bit different . . .

First, the mold release must've seeped under the master because it dissolved the hot glue holding it in place(!!). I wiped down the foamcore and the bottom of the master with a paper towel, and re-hot glued it.

Once that cooled, I mixed and poured the rubber, but then discovered that I didn't make quite enough material - it covered all but the "highest" part of the master! No worries (because: test).

And as if that wasn't bad enough, as I was pouring the rubber, I noticed that other parts of the master weren't being covered - it was like the master was starting to float up. . .

Because is WAS floating up! Yes, the hot glue had failed to hold and the master was floating on top of the rubber(!!!)

Now, that just ain't right.

So I pressed the master back down into the rubber and held it in place with a stirring stick in one hand, while I used the other hand to hot glue a couple scraps of foam core onto a block of wood.

If necessity is the mother of invention, desperation is the father of ingenuity. Resting on the ends, the wood block wouldn't have been able to press the master down, so the little white bits are the foamcore scraps used to fill the gap between the wood weight and the sticking-up portion of the master. Of course, the wood is either warped or the ends of the box aren't quite level with each other. So the handy dandy baby powder bottle is resting on one side to keep the wood tilted properly.

I have no idea how this is going to work out. I already figure that the part of the master touching the wood/foamcore is going to poke through the mold. It really can't help but do so. So I don't think I'm going to be able to pour any resin into this mold (hmmmmm.... unless I use some duct tape to seal the little hole . . .)

Ah well. Again - this is only a test.

A couple of lessons so far:

  • Adhere your master to the bottom of the foamcore box using something that's impervious to mold release
  • Mix enough rubber mold material to cover the entire master, with rubber to spare (it should cover the highest part of the master by at least 1/8" preferably more)
Despite these hiccups (hiccoughs?), I'm actually enjoying learning this process. Resin casting - like soldering or airbrushing - is one of those things that's so mysterious in the hobby and I'm glad to be confronting my fear of failure and enjoying the journey. At the end of the day, worst case scenario is that I'm only out a little time and money. And the longer I'm in this hobby the more I realize that that's the price - literally and figuratively - of getting over some of these hurdles and developing some really useful skills.

Of course, I may change my tune when I see how this thing actually comes out . . . stay tuned!


  1. Sounds like you have the right attitude - give it a try, see how it goes, and adapt!

  2. Reminds me of a Rube Goldberg invention!

  3. Reminds me of a I love Lucy episode....