About Fiberglass Molds

Creating a product, a shell or part from scratch means learning the art of mold making. Fiberglass provides a great lightweight and durable material for finished auto, boat or hobby parts. It also makes for a great repairing tool where structural or cosmetic damage are found. Fiberglass moldings, the actual parts and pieces being reproduced, can be made from fiberglass molds. Why use fiberglass and what is involved in the basic mold making process?

Why Fiberglass?

Traditionally, fiberglass was a term used to describe thin glass filaments but is now used to describe a two-part process using a glass fiber reinforcement material combined with a plastic resin. The advantages of fiberglass include its strength, light weight and its use as a structural reinforcement for other materials. Fiberglass can be bolted to, bonded to, sanded, filed, drilled and sawed.

Where to Use Fiberglass Molds

If you can imagine it, a fiberglass mold can probably be made for it. Fiberglass is used for boats, automobiles, airplanes, furniture and sculpture. Many automobile restoring enthusiasts learn to create their own fiberglass molds to replicate lost or no longer made parts. Sometimes parts or projects require more than one mold to achieve the final part. This is called a multi-part fiberglass mold.

Making Your Own Fiberglass Molds

There are two types of fiberglass molding --- contact molding and pressure molding --- and many variations of each. Contact molding is accomplished either by hand lay-up or spray-up techniques. But often it is a combination of the two. Pressure molds are a more expensive process and are accomplished through matched die molding, pressure bag molding and vacuum bag molding.

What's A Plug?

Molds are made from a plug, also called a buck. The plug is the shape the mold will be made from. This is the creative part of creating a fiberglass mold. Not all items are easy to "plug" and some items don't exist for an exact representation, or plug, to be made from. Plugs can be made from any number of materials --- wood, plaster, concrete, clay, plastics or a combination of materials. The plug should be as exact as possible to the original shape.

Making Molds From Plugs

Once your plug is made, it's time to make a mold from it. The mold comes together, referred to as the "lay-up," in this order:
1. The plug gets coated with a releasing agent.
2. A tooling gel coat is then sprayed on and allowed to harden.
3. A layer of fiberglass mat, usually a polyester resin, is added.
4. The mold is stiffened by alternating layers of mat and woven roving.
5. Additional reinforcement may be needed to keep the mold from sagging or flexing.
6. All resins are allowed time to cure.
7. Remove the plug.
8. Create the molding.