Making a Fibreglass Part From Oil And Dirt

First ensure that the mould you have for your fiberglass part is free from oil and dirt by washing it in clean warm water. Allow it to dry out completely.

Release Agent

To ensure the fiberglass part doesn't stick to the mould you need to apply a release agent. For best results we recommend the use of a paste wax followed by a PVA release agent. Start by applying two coats of the paste wax to the mould. This can take the form of a brush-on or aerosol product. We prefer the aerosol product for speed and smooth application. It is vital to keep the release agents as smooth as possible as this can affect the surface of the finished casting.

After allowing the initial two coats of paste wax to dry for at least 30 minutes you can start applying the PVA release agent. We use a soft sponge to apply this coating as we want the surface to remain streak-free. We find a brush tends to leave streaks which can show up in the surface of the finished fiberglass part. Make sure that you cover the entire area of the mould with the release agent. Keep checking for any runs in the release agent and smoothen them out with the sponge as soon as you notice them.

Now allow the PVA release agent to thoroughly dry. You can speed up the drying process with a hair dryer if necessary.

The Gelcoat

A gelcoat is the initial first coat of resin which will ultimately become the visible surface of the part you are creating. This coating of resin does not contain any reinforcement such as fiberglass matting so that it can be as smooth as possible. Reinforcement of the part will come in subsequent coatings to the back of this initial gelcoat.

1) The first step is to work out how much gelcoat you need for the part. You can work this out roughly by estimating the surface area. 1 square meter of mould surface usually requires about 500ml of gelcoat .

Once you have your estimate pour the right amount of gelcoat resin into a mixing container. Mixing containers can be as simple as a waxed paper drinking cup or for larger amounts of resin you can use an ice cream container.

2) Now we need to work out how much catalyst we need to set the gelcoat resin. The catalyst we need for gelcoat polyester resin is a dangerous chemical call MEKP and should be used with great care.

So for example if you are wanting to mix 500ml of gelcoat on a cold day you need to work out 2% of your resin (simple calculation 0.02 x 500ml = 10ml) We need 10ml of MEKP catalyst when mixing 500ml of resin on a cold day.

3) Now we need to mix the catalyst and resin together in the mixing tub. Stir well using a flat stick such as a paddle pop stick. Using a clean brush apply the first coat of resin to the mould. Make sure the coating is thick and even.
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