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Tuesday, March 12, 2013

Basic Molding with RTV Silicone

This is just a very basic step-by-step guide to creating relief molds out of RTV. I've only recently learned how to do this myself, so I don't have a pressure pot, but I do hope to get one in the near future. I'm just making a quick tutorial with pictures to show my maker group what I've been doing. There might be some swears in here, I don't know. Luckily I took good, self-explanatory photos, so if my writing is painful, you can pretty much do this just by following the pictures.

Oh, before starting make sure the 24 hours you need for curing are not during rainy days. Humidity will put bubbles in your mold, and moisture will cause it to take longer to set.

1. First, you are going to need your RTV. I chose Econosil from Silpak Inc. This stuff has a 24 hour curing time, and you need to mix 10% of the catalyst B to the A-side by weight.
  2. Your materials needed for mixing are:
  • kitchen scale
  • RTV and catalyst
  • mixing stick
  • one plastic cup
  • one bucket that is large enough to hold the amount you will need to fill out your mold.

3.   Before you start mixing, you are going to need to set up your molds. First, I used a hot glue gun to glue my pieces for molding onto the surface that I was going to pour the silicone into. I cut a large Pepsi cup in half so that I could use that as the wall of my mold. For the bottom of the Pepsi cup all I had to do was glue my skulls into it, but for the top I needed a smooth surface to glue my hearts and stars onto, and then I needed to hot glue the rim of the cup to that surface. What I ended up using was the top of a cookie tray from the supermarket.
 
4. Now, you need to measure out the amount of side-A that you are going to need to fill out your mold, because this will be the greater amount. For side-B you will only use 10% of the amount you used of side-A by weight, and it is very important to get it exact, so you must use the scale for this part. In my example I used 10 oz. of side-A, which means I only needed 1 oz. of side-B.

5. Now, mix the crap out of that shit, making sure to scrape the sides. It needs to turn a nice, uniform light blue color.





6. Once you are certain that you've mixed every particle of side-A with side-B, you can start pouring your mold. When you pour, don't move the cup around to try and fill in spaces, because this will create bubbles near your pieces. Instead, just pick one side and pour from there until your pieces are completely covered. Make sure you have enough RTV above your pieces that if your mold springs a small leak, it won't sink down to uncover some areas.

After you've poured every bit of RTV, you might want to vibrate your mold a bit to try and get the bubbles to the surface and away from your pieces. I put my molds onto a filing cabinet, and pounded the ever-loving hell out of it to shake as many bubbles out of it as I could. It still won't get as many as a pressure pot would, but the bubbles are going to be rising throughout the time it's setting anyway, so as long as you've poured right, you shouldn't have any touching your pieces.

7. Wait 24 hours.

 8. Oh look, it's done! Also, the one I set on the cookie tray sprung a leak, so I guess it's not really a good surface to use hot glue on. My mold turned out alright, though.

Peel whatever you used for the wall of your mold off now.



9. Now pop the bottom off, making sure to be careful if you don't want to break your originals. You will see that a little bit of silicone has probably gotten underneath your pieces. That's no problem as long as you have an X-acto knife or a small pair of trimming scissors. Just pop the pieces out, and trim the excess silicone off.

And there you have it! Your very own silicone mold. With this, you can make STUFF.




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