Fiberglass Armor Construction: Prepare Mold
Prepare the Mold for Fiberglass
Now that the mold is all cured it is time to demold from the original model. It is always wise to be careful, and take your time, with demolding. Mistakes can damage the mold or the model. In a lot of cases the model will get damaged even if you do everything perfectly, since it is made out of a soft material. The more you can minimize damage the better. If there is a problem with the mold and you have to recreate it having a model in good shape will save a lot of time. (If the model is ruined in the demolding process and you have to make a new one, use the mold, with its flaws, to pour hot plasteline into (be very careful!) and let it cool, then you can use the new model created from the mold, and just fix the parts that the mold has wrong.)
Depending on the shape of the mold you may or may not be able to take the plaster layer off first. If you can this is best, but with some shapes and in some instances you will have to pull the two off together. First see if there is any plaster that is sticking to the base that needs to be cut off. If there is you can either break it off carefully with a hammer (usually for a piece that sticks out) or use something like a Dremel with a cutting wheel to cut it off. Make sure to use eye protection and wear a mask if you use the cutting wheel, also do this outside, if you can, as the plaster dust that is created is very fine and gets everywhere. Then just pull the plaster mold away. If you have to you can use a few screwdrivers or other tools for leverage to pop it off. If you damage the plaster mold a bit it is not big deal, it is only for support and all the detail is in the rubber mold. If you are doing the plaster mold only route I wish you luck!
Once the plaster mold is free you should be able to just peel off the rubber mold. Once it is off be sure to store it in the plaster mold. It should fit in it perfectly, with every nook and cranny matching. If it does not, try wiggling it around a bit until it does.
Once the rubber mold is out take a close look at it. Did any bits of paint or plasteline stick to it? If so clean those off. Once the rubber mold is all nice and clean you can prep it for laying fiberglass right away.
Fiberglass resins are really powerful adhesives. They stick to most everything and do so very strongly. This is why fiberglass is such a great and strong material. Because of this it is advisable to use two different release agents in a mold with fiberglass.
There are a few different materials that can be used. The main three I have worked with are PVA, Vaseline and wax. After using different combinations I found I liked the PVA and Vaseline combo the most. (The PVA is actually a chemical that can be put directly onto resin once it has begun to set (a gel coat, for instance) to cause the outer layer of resin to properly set. The hows and whys are not really relevant, but if you are interested I suggest doing a bit more reading and picking up a book on working with fiberglass.)
First you will want to brush a layer of PVA into the mold with a foam brush. The foam brushes work really well for this since they are spongy and can suck up extra PVA if you put too much down. Give the PVA ample time to dry.
Once the PVA is dry take another foam brush and paint on a layer of Vaseline. If you want you can heat the Vaseline to make it softer and easier to paint on. You want a nice greasy layer over the whole mold. Be sure to cover the whole thing, even the area beyond the edges in case any resin spills there or the fiberglass is laid past the edge of the piece (which is how I usually do it, then I just cut the edges away)
Once the Vaseline is on the mold you are ready to start laying the fiberglass.