Gelcoat

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A gelcoat is a material used to provide a high quality finish on the visible surface of a fibre-reinforced composite material. The most common gelcoats are based on epoxy or unsaturated polyester resin chemistry. Gelcoats are modified resins which are applied to moulds in the liquid state. They are cured to form crosslinked polymers and are subsequently backed up with composite polymer matrices, often mixtures of polyester resin and glass fibre or epoxy resin with glass and/or carbon fibres.

The manufactured component, when sufficiently cured and removed from the mould presents the gelcoated surface. This is usually pigmented to provide a coloured, glossy surface which improves the aesthetic appearance of the article.

Many marine craft, including large yachts, are manufactured using composite materials and the outer layer, or gelcoat, is typically 0.5mm - 0.8mm in thickness. Gelcoats are designed to be durable, providing for example, resistance to ultraviolet degradation and hydrolysis.

Specialised gelcoats can be used to manufacture the moulds which in turn are used to manufacture components. These require very high levels of durability to overcome the mechanical and thermal stresses encountered during the curing and demoulding processes.

Suitable resin chemistries for the manufacture of gelcoats vary, but the most commonly encountered are unsaturated polyesters or epoxies. Within each of these categories, the resin chemistries are further subdivided.