** Please be aware that the information provided is a general guideline not the rule. Using fiberglass and resin is more of an art than a science. Experiment before diving into your project.
The first step to making a mold is having a plug. A plug is the exact shape and dimension that you want your final part will be. Often times, a replica is made of an existing part, such as a car bumper or of a canoe. Other times, modeling clay, wood, or sheet metal is formed into the final desired shape. If wood or plaster are used, it will need to be sealed first with lacquer or resin. This is because they are porous.
The plug should be buffed and sealed followed by a mold release. Mold release can be time consuming but is an essential part of mold making. A wax, such as Partall #2, is commonly used first. Five coats is a good number to make sure it is well coated, buffing after each layer. For security, a PVA is used after applying the wax. PVA is a plastic dissolved in alcohol. It is sprayed (recommended) or brushed on, allowing thirty minutes to dry. Three coats should be applied if you want the best possible release. Spraying with a fine paint sprayer works the best. The first coat should be a light mist and then followed by two or more heavier coats.
Tooling Gel Coat
After a mold release (or two) is added, tooling gel coat can be used. Tooling gel coat gives the mold surface a strong, scratch resistant surface. It typically comes in black or orange to be able to tell the difference between the part and mold. (We carry black tooling gel coat). Do not want to use a gel coat with wax in it for this step. It is recommended to spray the gel coat on instead of brushing. Spray a thick layer of gel coat on the plug. The layer should be between 15 and 20 mils. Allow to cure for two to four hours, or until the gel coat can not be scratched with a fingernail, but is still tacky. (If the layer is not mostly cured, the styrene in the following coat may cause it to wrinkle, also called alligatoring.)
The next step is to add the fiberglass fabric. A layer of fiberglass mat should be used as the first layer. This helps prevent print through (when the fabric weave can be seen through the tooling gel coat). A general purpose polyester laminating resin or ISO Resin is commonly used as the resin. The ISO resin is a tooling resin which shrinks less than the general purpose resin. This may not be a factor for most parts, but large molds or final parts with critical dimensions should use the ISO resin. The resin should be mixed with MEKP at a 1% to 2% mix ratio. The mat could be wet out with a brush or spreader. Then, the resin can be worked in with a bristle roller. An aluminum roller can be used to force out all the air. When that is done, there should be no white fibers or air pockets visible. Let the resin cure. When the resin is hard, but still tacky, the next layer can be added. Multiple layers should never be cured at the same time. This could cause warping, especially in large molds. Additional layers of mat and/or cloth can be added to give the mold strength. An additional 3 layers of 1.5 oz mat is usually sufficient, depending on the application. Be sure to allow adequate curing time between layers.
Allow two or three days for the mold to cure completely. Use a plastic wedge or sharpened paint stirrer (never use hard or metal tools) to slide between the mold and plug. If there is excess resin or fiberglass hanging over the edge of the plug, it will need to be cut off so the plug can slide out. Separate the entire edge of the mold from the plug. The plug should now be ready to separate from the mold.
The mold can now be prepared for use. Most times, the mold will need to be sanded and polished. Use 220 grit and progress to a 600 grit sand paper to sand the mold. Afterwards use a polishing agent such as, Aqua Blue 100 and 200 to polish the mold. It is important to use a sealer to seal the mold (we sell Orca Seal Mold Sealer). Wax and buff with Partall #2 and coat with a PVA. For the first 5 parts off the mold, use Partall #2 AND PVA (such as Partall #10 or Fiberlease) again. This should fully season the mold. Apply Partall #2 after each part going forward.