Fiberglass Resin and Casting

[Weapioneer]

Greetings,
I am making the Armour of Altair costume from Assassin's creed II, and I am planning to make the left gauntlet, the one with the symbol of the assassins, and the belt insignia out of resin. I am planning on sculpting the insignia from plasticine(play doh), pouring plaster of paris on top of it in a box, then removing the block of plaster, cleaning out the plasticine and pouring Fiberglass resin inside.
However, have not found anyone else who used this method, though some people have used plaster for molding. Can someone please help me fill the gaps in my knowledge?
Plasticine becomes soft with heat, and plaster cures exothermically. Is this going to make a mess? What common house hold materials can be used as a release agent, like WD-40 or cooking oil? Any important thing i should know before i start doing this? or is it a completely stupid idea?
Thanks

 

[Pete SSS]

Casting fibreglass into a plaster mould is a fairly standard practice, that's how I was first taught how to use glass.

One thing you must remember to do however, is seal the plaster mould before you try to make a cast. Both Polyester and polyurethane resins are very picky about water. They will bubble, or not cure at all if they are exposed to any moisture.

The hardened plaster, even when cured, will still be holding a lot of water, so you must seal the plaster to trap the moisture.

You can use shellac to do this, or even PVA white glue. But I'd prefer shellac. After you have cleaned the plasticine from the plaster, just brush a few coats into your mould, and once its dry, you'll be ready to go.

Another thing to consider, is that you will almost certainly have to break apart your plaster mould to get your cast out of it. I suspect there will be LOTS of undercuts in your sculpt, which will pin your cured cast into the mould. This is perfectly normal, it's known as a "waste mould" meaning that, once you have your cast, the mould will have to be broken off the cast, and can't be used again. This is why, if we want to make more than one cast of a certain piece, we use silicon moulds.

I wouldn't worry about the reaction of the plaster melting your sculpt, but if you are concerned, you can always do a test with a lump of plasticine and a quick tes.t mould. Again, bear in mind that the larger the area of plaster you pour, the greater the temperature will get.

Hope that helps a bit, good luck!

 

[Weapioneer]

Thanks! I think i have some PVA glue around, so i will use that. Also, I heard that mixing some PVA glue into your plaster when making it will make it stronger, is it a good idea to use it here?