How to Make a Fiberglass Mold with Styrofoam
Fiberglass, a material most often used for casting prop objects, is also useful in making molds of plastic or Styrofoam template objects. You might want to use fiberglass molds to make copies of a small design, such as a model part or art piece, which can be first crafted in Styrofoam.
Things You'll Need
- Styrofoam object
- Clear sealer
- Modeling clay
- Liquid mold release agent
- Wax mold release
- Latex gloves
- Fiberglass cloth
- Fast hardener
- Colloidal silica filler
- Graphite powder
- Tooling gel coat
- Paintbrush and stirring tool
Carve the piece of Styrofoam for which you would like to make your fiberglass mold. Shave and finish the outside of the Styrofoam object so that it is as smooth as possible, then coat the Styrofoam in a clear sealer and let it dry.
Find the middle line of the Styrofoam object and mark it out, from one side of the base, over the top, to the other side of the base. Along this line, build up a thin wall of modeling clay that is at least as tall as you would like your fiberglass mold to be. Smooth out the modeling clay so that the division between the two sides of your Styrofoam object is as thin as possible.
Apply wax mold release to both sides of the Styrofoam object and the modeling clay in several layers, buffing as you go along until your layers are fairly smooth. Apply a full layer of liquid mold release over the wax mold release, and let this layer dry completely.
Gather your resin, tooling gel, silica filler, fast hardener and graphite powder together in a protected, well-ventilated work area. Mix together a small batch of resin, following the instructions on your particular product. Add to this resin mixture a small amount of colloidal silica filler, fast hardener and graphite powder so that your resin will dry more quickly and effectively. Pay attention to the products' packaging recommendations.
Paint a little resin mixture into the grooves and corners on one side of your Styrofoam object, then let the resin dry completely. Over the hardened resin, paint a full layer of tooling gel coat, still working on only one side of the Styrofoam object. Let the gel coat dry for 30 minutes. In the meantime, mix together another batch of resin, tooling gel, silica filler, fast hardener and graphite powder.
Apply a coat of resin mixture over the dried tooling gel coat. Cut several strips of fiberglass cloth and lay them over this coat, pressing the fiberglass into the wet resin. Let the resin dry, then paint another coat of resin over the fiberglass cloth. Continue adding layers of resin and fiberglass cloth to the side of the Styrofoam object you are working on until you have the desired thickness. Let the resin cure overnight, then remove the modeling clay and perform Steps 4-6 on the opposite side of the Styrofoam object.
Pull the fiberglass mold halves off of the Styrofoam, separating the halves at the center split. Trim the rough edges of the fiberglass mold and clean it of all clay.
- Never touch resin with your bare hands or let it get on your skin. Follow all safety precautions detailed on your product packaging.