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Gel coat or top coat? Where's the difference?

The question of whether gelcoat or topcoat has to be answered with regard to the application.

Characteristics of Gelcoat

Gelcoat is used when a negative mold is available. Gelcoat is usually the first layer (fine layer) that is applied to the mold.
Gelcoat cures to become adhesive on the air side, making it easier to drape the reinforcement fabric into the mold.
Gelcoat can be colored with color pastes.
By adding paraffin, gelcoat can be adjusted so that it cures tack-free on the air side.
Sanding is not necessary when further processing gelcoat.
Gelcoat is available as an epoxy gelcoat based on epoxy resin, as well as a polyester gelcoat based on polyester resin.

Top coat properties

Topcoat is always used when a product already consists of fiber composite material and the fine layer has to be applied to the laminate, such as in pool construction, boat repairs, etc.
Top coat cures without tack.
Topcoat, like gelcoat, can be colored with color paste.
Topcoat can only be laminated on if it has been sanded beforehand.
Topcoat is available as an epoxy topcoat based on epoxy resin, as well as a polyester topcoat based on polyester resin.
A more recent application for crystal clear epoxy topcoat is for sealing wood and canvas. The application of crystal-clear epoxy top coat creates a protective layer with a slight three-dimensionality.

Basic information on gelcoat processing and topcoat processing

In contrast to the normal application of paint, gelcoat and topcoat do not dry, but harden. A minimum layer thickness is required for curing. The layer thickness is usually 0.3-0.5 mm. This is particularly important with the polyester top coat, as paraffin is washed out to the surface during hardening. This paraffin layer acts like an internal separating layer. If the tocpoat does not harden tack-free due to the layer thickness being too thin and it is necessary to apply the tocoat twice, the first layer must be sanded down.