I have been researching fiberglass molding solutions, for a potential run of parts in the future.
It seems that brush-on silicone molds cost about as much as epoxy-based fiberglass molds (both materials cost ~$10/ lb).
It would seem like silicone is the best material: it flexes, doesn't require extensive waxing to prevent bonding with the epoxy, and is more gentle when releasing from the cast pieces/ original master object.
But... plenty of shops choose composite molds over silicone, so I want to ask:
What is the benefit of using composite molds? Do they last longer than silicone, etc?
Its a complicated answer which, its kinda folly to approach it from a financial perspective as the cost of materials fluctuate greatly year to year, even week to week, and post COVID even more so with supply shortages being taken advantage of to just mark up everything. Damn you capitalism lol.
That said it comes down to the type of prop or replica one is creating, the size, and yes even long term shelf life for the mold itself.
Silicone is good for solid objects normally as the flex of the material makes it easier to peel off of more rigid material. The larger a mold is though, the more you need to think about reinforcing it so the mold itself doesnt warp while the material is curing. There are a number of ways to make a exo-mold around a silicone one, one of the most cost effective ways I've seen it done is using a silicone interior mold with a plaster exo-mold to hold it in place. Fiberglass however becomes more suitable as it is lighter, but will still retain its shape and keep a silicone from warping while a mold is being poured and then settled.
Fiberglass overall is a go to for large scale molds. Working in a creature shop for a few years it did make all the difference when it came to large molds to pour a creatures leg or arm or a whole creature suit, to have the same mold in plaster would just weight too much to effectively utilize it or to have the same mold as a solid brick of silicone would also be just as heavy but also unwieldy and also would warp under its own weight resulting in a faulty casting.
That said when it comes to shelf life usually the BIG molds that are composite Fiberglass with silicone cores last very long, even in outdoor weather as plenty of creature shops dont have the interior space to house their molds, so they need to house them outside. Plaster molds with a silicone core are second when it comes to longevity. Silicone molds always need to be stored indoors in temperature controlled environments to keep them from drying out as they will crumble over time. I've seen some large scale silicone molds, but they do need alot of maintenance and even when pouring them they need bracers, rubber bands, and other contraptions to keep them from bowing or buckling under their own weight and the casting being warped in return.
Hope this gives you some good insight. Good luck on your future crafting.
-Josh
