Mold Making: Two Part Silicone Mold

Step 7 FAQ

*UPDATE* I'm going to include some FAQ's to answer some of the questions I've received.

---

• Q: What resin did you use? What sealant did you use to prevent it from sticking to the mold?
• A: I had decent luck using crystal clear spray varnish as a sealant. I would recommend you use mold soap or SuperSeal to coat the mold. Spraying a coat of PVA in the mold before casting will also provide a solid seal. For casting parts out of your mold, silicone usually doesn't need any release or sealant, but the particular resin I was using met some cure inhibition against the RTV. You can find a non polyester clear casting resin and it will probably cast fine without needing any release or sealant.
• Q: Is the mold reusable?
• A: The mold is completely reusable. Cured silicone has an average shelf life of five years and will hold up to thousands of castings. It will break down depending on what material you use, but that's still in hundreds of castings with the most abusive materials. You'll know when the mold's at the end of its life when it's not flexible and begins to yellow.
• Q: Where can you get silicone and other molding materials? How much will they cost?
• A: Good silicones can go for $100/gallon and more. You're going to pay more per oz by buying smaller batches, but it's easier to live with the expense. The material I used comes in a 2 pint batch at $22 { manufacturer's site }. The polyester resin I used was CastinCraft clear resin, and cost $15/pint. You can pick this and the colorants I used up at most craft stores. I also used SmoothCast for the white model you see below and C-1515 for the translucent model. Each of these are about $15/pint as well. For more resources, you can check Smooth On, Freeman Casting Supply, and MicroMark.
• Q: Silicone is too expensive. I heard you can use molding rubber. How is it used?
• A: Actually, if you're using a molding rubber, your process is a little different. When you take out your original part, and lay it up in clay. Before you pour your rubber over you'll need to coat it in a molding sealant and then a release. I recommend you use something like PVA, liquid floor polish wax (wax is both a seal and a release), SuperSeal, or Mold Soap. SuperSeal is pretty easy to find, and usually comes in a spray bottle. Personally, I love the mold wax. You'll want to clean up everything with a soft brush if you see any streaks. Then you apply a release like EZrelease, or Universal Mold Release. After doing all that, you can pour up your rubber. Wait for it to cure, flip the mold, clean out the clay, repeat the seal/release process and pour again. Once your mold cures, you remove the piece, apply a coat of seal to the mold, and then a coat of release (this is why I prefer silicone, because you don't have to fiddle with releases.) After everything is sealed and released, you should be ok to cast. If everything's done right, you should be able to produce some nice shiny pieces. Allow the plastic to cure overnight and wake up to some brand new toys.

Comments

[bluebel95]

Can I use it to make cakes or gummy candies? :)

[spiderham]

Corn starch is used for gummies. Just spread the powder into a tray, press your master into the it and pour slowly into each cast. This is the method used at a candy shop I worked at some time ago. Once set, dump the whole thing over a screen and reuse the powder.

[Sheilauva]

I am using window silicone, clear, sealant for my two part molds. I have not done this in 15 years and have forgotten what to use for a release, not for the clay, but for the seams around the clay. The silicone will stick to itself, so what do you use for the second half of the mold. Does this make sense?
Can I use canola spray on the silicone to release or vaseline, or do I have to buy a can of silicone release?