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→Using a Mould
To make a mould, you start with a plug in the exact shape of the hull or hull component. The plug is disposable, and can be made from a variety of materials. The exterior of the plug is highly finished.
Next, a fibreglass mould is built up on the plug, using alternate layers of cloth and matt, a felt-like material. Each layer is impregnated with a synthetic polymer resin that cures and hardens. The exterior of the mould is reinforced, and the plug is removed and discarded. The best range for working temperatures in the mould shop are is 18-21 C °C with humidity less than 80%. Direct sunlight should be avoided.
Finally, the inside of the mould is coated with a wax-like release agent, and a fibreglass hull or other component is built up inside, starting with the coloured gel coat, a layer of mat and then woven roving. Putting mat, a sort of filler, next to the gel coat prevents print-through of the roving. Anecdotally, putting mat next to the gel coat increases the propensity for blistering. After the piece is finished and cured, it is removed from the mould for finishing. The mould is then ready for re-use. Gel coats should be >30 mm and incorporate protection from ultraviolet (UV) light, which damages plastics.