Gelcoat application: The importance of paint brushing for a premium result.

In the yachting industry, gelcoat is mainly used to give colour to the boat and to make the product waterproof, creating a barrier between seawater and weathering on the one hand, and the moulding on the other, especially that of the hull, i.e., the part that is always immersed in water and subject to the risk of osmosis.

Generally, there are two methods to apply gelcoat to the moulds before layering with fibreglass and then making the moulding.

Gelcoat application can be done:

• manually with a brush (using a low-pressure pump with gelcoat gravity drop)
• by spraying, with a high-pressure pump.

The gelcoat used by Absolute is of the Neopentyl Glycol (ISO-NPG) type, composed of resin, styrene and pigment.

Styrene is a solvent added to the resin in varying percentages, depending on the type of application. The higher that percentage, the less pure the gelcoat that is used (thus affecting its protective properties).

• For spray application, styrene is added to the resin in a percentage of 38%.
• For brush application, styrene is added at a percentage of 28%.

The approach used by Absolute involves manual application, utilising a brush and drip method for the gelcoat. This method enables the material to be used with its natural density and in well-defined percentages of the products required to produce it.

The application is done by applying a first longitudinal layer. Once the material from the first application has polymerised, a second transverse layer is applied so that the thickness of the gelcoat is consistent at every spot. The material is applied through specific brushes, which must be replaced at regular intervals after a certain amount of product has been applied.

Working in this way can achieve up to three times the thickness compared to the spray method. It also provides greater durability, especially in terms of yellowing and gloss maintenance (multiple cycles of surface polishing are possible during the life cycle of the boat).

The so-called “spray” method, on the other hand, involves applying gelcoat through compressed air.

In this case, to avoid dripping, stagnation of material, formation of shrinkage and wrinkles, lack of gloss effect and color changes, which would result in poor quality of the final product (particularly with the use of complex and highly shaped molds), the gelcoat must necessarily be applied at once, without allowing it to polymerize.

A significant part of the compressed air used to release the material from the gun remains trapped in the gelcoat itself, creating a non-homogeneous surface barrier that is much more exposed to aggression by seawater and weathering. In addition, in case of interventions on the completed structure, such as sanding on the surface, micro-dots due to the imprisoned air during spray application would be evident, highlighting the intervention itself. With this application method, cases of osmosis are more frequent.