Casting, a common process in creating fiberglass objects, involves making the final copy of an original design or template. During this process, you apply the casting material to a mold, which is a negative version of the original design, in order to create the desired shape. Fiberglass casting is often used to create pieces for boats and automobiles, and has been a popular material in professional as well as hobbyist prop making for many years.
Prepare the Mold
Arrange your materials in a well-ventilated work area with covered surfaces. Put on your latex gloves, safety goggles and vapor respirator prior to fiberglass casting.
Spray the inside of your mold with a mold release agent, so that the fiberglass will not stick permanently to the inside of the mold, and let it dry completely.
Mix up a tiny batch of resin in a bucket or plastic cup. Pay attention to the packaging directions for your brand of fiberglass resin, as they will not be the same for all brands.
Apply a thin layer of resin to the inside of each mold half with a paintbrush, creating an impression coat that fills in all the crevices and corners. Let this impression coat dry.
Mix up another small batch of resin and paint another layer over the impression coat. Cut your fiberglass cloth into small strips and place a few pieces into this layer, letting the resin soak into the cloth.
Wet the fiberglass cloth by applying more resin over the cloth, until it has soaked up as much resin as possible. Continue covering the entire inside of each mold half with a layer of wet fiberglass cloth.
Cast the Fiberglass
Let the first layer of fiberglass cloth dry slightly, then apply another layer of resin and cloth to the mold halves. Build up several layers until you have the desired thickness, making sure that the layers of cloth stick together.
Let the fiberglass dry for a few hours, then carefully remove it from each mold half while it is still flexible. Place the flexible fiberglass pieces back into the mold halves to continue curing overnight.
Take the fiberglass cast halves out of the mold. Tape the pieces together with masking tape as a temporary measure.
Mix together a small batch of resin. Lay a few small fiberglass strips over the gap between the fiberglass cast halves and paint resin over the strips to adhere them to the cast. Remove the masking tape while you work.
Leave the fiberglass cast to dry overnight again. When dry, wear a particle mask and safety goggles to sand down any rough patches on the cast.
Clean up your casting work area with turpentine, which will take care of any spilled resin.
Fiberglass is extremely toxic. Be sure to cover your skin and eyes, and do not breathe in any vapors or dust from the material.