Although fiberglass is most often used as a casting material, it can also be used to make molds. Fiberglass molds are best for complex projects that may need to be cast over and over, as fiberglass holds up well over time. The materials are also relatively cheap, compared with other molding materials. To make a two-part fiberglass mold suitable for casting in plaster, complete the following instructions.
Instructions
1. Find a template object that you wish to make copies from. You can also make your own template from foam or balsa and finish the outside so that it is smooth. Determine the midline of the object, from one side of the base to the other, and build up a wall of modeling clay or place a parting board with modeling clay there, so that you can keep the mold halves separate. Make sure that you have as smooth and small of a seam as possible.
2. Apply several layers of wax mold release to the entire object, buffing the wax so that it is as smooth and bubble-free as possible. On top of the wax mold release layers, apply a coat of liquid mold release. Let the mold release dry for as long as directed on the product packaging.
3. Mix up a small batch of resin, tooling gel coat, fast hardener, silica filler and graphite powder together, following the directions on the packaging. Working on one side of the object, brush a thin layer of this resin mixture onto the edges of the template object, starting with the corners. Let the resin dry, then apply a layer of gel coat over the rest of the template object as a base coat. Let this coat set for at least a half-hour.
4. Mix up another batch of resin and apply a thick coat over the gel coat. Over this wet resin, lay down small strips of fiberglass cloth, allowing the cloth to soak up the resin. Let this layer dry for a half-hour. Continue applying layers of resin and fiberglass cloth until you have a good thickness, then let the fiberglass resin cure overnight.
5. Remove the wall of modeling clay and clean all clay from the mold. If desired, cut keying marks into the fiberglass mold halves so that they will fit more accurately together when you start casting. Repeat Steps 3-5 for the other side of the template object, right up against the first mold half.
6. Trim the rough edges of the mold and separate the mold halves. Prepare the mold for plaster by coating the mold in a mold release agent.
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