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Gelcoat - Things to know about gelcoat

The top layer of a fiber composite material is referred to as a gel coat. This is the top layer of a component made from a negative mould.

Gelcoat is available both as an epoxy gelcoat based on epoxy resin and as a polyester gelcoat based on polyester resin.

Furthermore, gelcoat can be presented both in a crystal-clear version and with its own color. Crystal-clear gelcoat, especially epoxy gelcoat, has the advantage that it can also be used for visible parts (especially visible carbon parts).

A special feature of gelcoat is that it hardens sticky on the air-side surface (i.e. not the side facing the mould). This makes it easier to drape the reinforcing fibers, such as glass fiber mats, into the mold later. Covering the gelcoat with a PE film or PP film helps to allow the gelcoat to cure on the air side, e.g. for repairs without tack. In the case of the polyester gelcoat, non-tackiness can also be achieved by adding paraffin.

Gelcoat is usually applied to the mold surface as the first layer without reinforcing fibers and later forms the visible side of the product.

Gelcoat is not only used to improve the appearance of a component, but also fulfills other tasks. It increases the durability, weather resistance, corrosion resistance and surface quality of the product.

In order to reduce the flowability of the polyester gelcoat, silica is usually added to the gelcoat.

Because the gelcoat layer is placed in a negative mold without reinforcement fabric, the result is a clean and smooth component surface. This can be seen very well in boats or mobile homes.

Furthermore, gelcoat can be colored through by adding color paste. If the gel coat is applied in several layers, a colored layer is created. It is important to choose the color pastes according to the resin base. Polyester gelcoat can only be colored with polyester color paste and epoxy gelcoat with epoxy color paste. Incorrect admixture of color paste to the associated resin base can result in a sticky cure.

A more specific gelcoat is the mold making gelcoat. This gelcoat is used to make negative molds. Depending on the version, it is characterized, for example, by high scratch resistance or good sandability. Mold making gelcoat is available as both epoxy gelcoat and polyester gelcoat. As a rule, this special gelcoat is colored dark (usually black). This means that both the even application and the unevenness of the shape can be better recognized.

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