Make a Mold for Fiberglass
Fiberglass, although a fairly toxic substance, is a common choice among professionals, students and hobbyists for creating props and other art projects. In order to form fiberglass into the desired shape, it must be pressed into a mold, or negative impression of a sculpture. The best molds for casting in fiberglass are made from plaster. They are usually made in the two-part style, since fiberglass dries too hard to peel out of an enclosed mold.
Instructions
1. Sculpt your original design or model object from water-based clay. Coat the entire sculpture with a clear sealer, such as Krylon Crystal Clear, and let it dry completely.
2. Visualize dividing the sculpture in half, creating two identical sides. Along this dividing line, build a thin wall of modeling clay that is a few inches tall.
3. Mix together a small batch of plaster. Add gypsum and water to your bucket until you have a soupy texture. Stir the mixture to remove air bubbles.
4. Paint an impression coat on one side of the sculpture, all the way up to the modeling clay. Let the impression coat dry to the touch.
5. Cut your burlap into small strips. Paint another layer of plaster over the impression coat, then press pieces of burlap into the plaster.
6. Paint more plaster over the pieces of burlap, then let this layer of the plaster mold dry to the touch.
7. Add more layers of plaster and burlap until you have the mold thickness you like. Let this half of the mold dry completely.
8. Repeat Steps 4 through 7 on the opposite side of the sculpture. Let the entire mold cure overnight.
9. Peel the halves of the two-part mold apart, and scoop out the clay inside. Clean the mold completely with warm water, leaving no traces of clay behind.
10. Coat the inside of the mold halves with mold release, so that the fiberglass does not stick to the inside. Let the mold release dry before you begin fiberglass casting.
