How to Make Fiberglass Plastic Molding

Fiberglass moulds are used to make several copies of shapes that may be difficult. These shapes may be an add size with odd angles. Fiberglass mounds are easy to make, inexpensive, are durable, and can be used to make items that have hundreds of parts.

To start the process you have to find something that you wish to make a copy of. In this example it is a vacuum formed cowl for a model kit. The shape can be copied using balsa or foam and a finish is applied to make it look glossy.

Plug preparation

A plug is needed to make a mound. The plug needs to be the exact shape and size of the final part. Replicas are often made of an existing part. In other cases wood, clay, or other material is used to form the final shape of what is going to be copied. If the plug is made from wood or plaster it is going to have to be sealed with a lacquer or a resin. It is suggested to use PR-301 or PR-311 for this. A coat of mould is also applied. To make sure everything is well sealed it is recommended to use five coats and buff the mold between each coating. For the best possible release three coats can be used. A find paint sprayer works well for this. The first coat should be a light mist and the two coats should be thicker.

Gelcoat

Gelcoat is used to give the mould a strong and scratch resistant finish. Tooling gelcoat comes in black or orange. Gelcoat is recommended in spray form as well as a thick coat on the plug. The layers should be between 15-20 mils thick. Allow the mould to sit for 2-4 hours until the gelcoat is tacky but cannot be scratched.

Fiber Glassing

When using this technique a layer of 1oz chopped strand mat is used first. General purpose polyester resin is then used. The resin is mixed with 1%- 2% MEKO. Be sure to wet the mat and work the resin with a roller. Use an aluminum roller to remove any air pockets. There should be no visible air pockets or white fibers.

Allow the resin to sit and cure. When it is hard add the next layer. Do not put several layers on at one time. this can cause the moulds to warp. Additional layers can be added for strength. Three layers of 1.5 oz mat is fine. Be sure to allow curing time before each new layer is applied.

Remove the Plug

Allow the Plastic Mould to rest for 2-3 days. Using a plastic wedge or a paint stirrer slide the tool in between the mould and the plug. Separate it completely. You should easily be able to remove the plug from the mold.

Now it is time to get the mould ready for use. It will need to be sanded and polished first.