Tuesday, October 9, 2012

Casting with Formaform

When I was constructing the troll costumes, I wanted to try something new in form of casting and mold making. Both of our trolls have harnesses with buckles, so I ended up casting the fastenings from polyester in a Formaform mold.

Formaform is a synthetic and elastic rubber material for mould making. I bought the smallest package, 1,25kg from Hobbypoint, Finnish crafting store. The package contains three different ingredients; granules, liquid and Thermolan, a type of a hardener.

The granules smells pretty bad, but its environmental friendly and you can use it over and over again by cutting it to pieces and melting it again. Nice plus if you haven’t made molds earlier and mess up the first ones, like I did. I think the process pictured below is my third try. Read the instructions well beforehand. You never know, if I cut some corners.

First you need to prepare the working space. What you need is a stove and a retired pot, a scale for measuring, wooden sticks or spoons and cardboard cups. Then you need a container for the mold. I used a juice tetra which I cut in half and strengthened with tape. The master piece is taped to the bottom of the contained with two sided tape. The wall of the mold should be at least 6mm thick. That should be taken inconsideration when choosing the container.

Before I started to melt the Formaform, I sprayed the master with silicone spray. Then I measured the ingredients; granules and liquid in ratio 100/40. I turned up the stove to medium heat, poured the ingredients in and started to stir carefully with a wooden spoon. You don’t want air bubbles. The stuff is ready as soon as it turns liquid. 

I poured the stuff on the mold container and checked the master’s surface for any air bubbles. I pushed the bubbles out gently with a paintbrush.

Then the mold needs to set. The time depends on the size of the mold from half an hour to hour. Formaform will turn rubbery. When that occurred I carefully removed the mold from the container and pulled the master out. I trimmed the edges and check the mold.

First two molds weren’t good enough, so I just chopped it up and melted it again. The third one was almost perfect, so I let the mold cure 12 hours before the next step. At this time the mold will lose some elasticity, but remain rather flexible.

 Because I was using really strong, industrial material for the casting I had to reinforce the inside of the mold. Otherwise the polyester pull would tear the mold apart. Formaform comes with a bottle of liquid that is used to make the mould heat resistant. It hardens the inside of the negative mold so that it can endure materials like resin and hot wax. 

I poured the liquid on the negative and let it set for ten minutes. Then I just poured the stuff out and let the mould cure until the inside had felt solid as the rest of the mold remained rubbery.

Then it was time to mix polyester filling with hardener and pour it into the mold. I recommend using a respirator and pair of gloves when working with irritating stuff. If possible work in steady conditions, in room temperature if possible and not in direct sunlight if you don’t want to ruin your cast or the mold itself. Again, been there, done that.

It took about 45 minutes for the polyester to cure to a point it could be pulled out of the mold. I let the buckle to harden overnight, trimmed it with utility knife and painted it.

In all, it was nice challenge to try something different and because I needed a handful of buckles, it was more affordable to cast them than buy them. And now I have materials for future projects. But next time I’m going to buy more suitable casting material, since the polyester filling I used was bit too strong for Formaform. The last pull I did tore the inside of the mold pretty badly.

If you want more information and approach to mold making, check Rullarinkeli’s blog. Instead of Formaform, she used Vinamold. And there are videos too!

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