Making A Fiberglass Mould

By Author: Jason Paget
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Fiberglass moulds are commonly used to make multiple copies of a part which may have a complex shape. Some of the advantages of using a fiberglass mould are: they are easy to make, the materials are inexpensive, and they will last for many years and can be used to produce hundreds of parts. The process starts with a pattern that you wish to copy. In this case, has started with a vacuum formed cowl from a model kit. This is a common part that any modeler may want to copy in fiberglass. The pattern could also be shaped from balsa or foam and finished to achieve a glossy surface.

Plug preparation

To make a mould, a plug is needed. A plug is the exact shape and dimension that the final part will be. Many times, a replica is being made of an existing part, such as a bumper for a car or a canoe. Other times, modeling clay, wood, or sheet metal is formed into the final shape. If the plug is porous, such as wood, plaster, it will need to be sealed first with lacquer or resin. The plug should be buffed and sealed with products such as PR-301 and PR-311. A coat of mould release will need to be applied. Five coats ...
... is a good number to make sure it is well coated, each time buffing afterwards. 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 ‘mist’ coat and the following 2 coats a bit thicker.

Gelcoat

Tooling gelcoat is used to give the mould surface a strong, scratch resistant surface. Tooling gelcoat comes in black or orange to be able to tell the difference between the part and mould. Spray (recommended) a thick layer of gelcoat on the plug. The layer should be between 15 and 20 mils. Allow to cure for 2 to 4 hours, or until the gelcoat can not be scratched with your fingernail, but still tacky.

Fiber glassing

A layer of 1 oz Chopped Strand Mat should be layed down as the first layer. General Purpose Polyester resin is commonly used as the resin. The resin should be mixed with 1% to 2% MEKP. Wet the mat out with a brush or spreader. Work the resin in with bristle roller. Afterwards, use a aluminum roller to force out all the air. When it is done, there should be no white fibers or air pockets visible. Allow the resin to cure. When the resin is hard, but still tacky, it is time to put the next layer on. Never cure multiple layers at one time because this may cause warping, especially in large moulds. Add additional layers of mat and/or cloth to give the mould 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.

Removing the Plug

Allow 2 or 3 days for the mould to cure completely. Use a plastic wedge or sharpened paint stirrer (never use hard or metal tools) to slide between the mould and plug. Separate the entire edge of the mould from the plug. You should be able to remove the plug from the mould.

It is time now to prepare the mould for use. Most times, the mould will need to be sanded and polished.

About Author:

Jason Paget from Elite Composites writes about Fibreglass Moulds. For more information on Fibreglass Moulds please visit http://www.elitecomposites.co.uk/