Gel coats are designed as a protective coating for structural laminates. They are available in brush and spray versions and are best applied at a thickness of 0.5mm. Most exterior gel coats are based on isothalic resins with low styrene emission and are available in both brush and spray forms. Nowadays, they are blister resistant and usually approved by marine authorities.  

   There are several types of gelcoat, each having its own particular function.   The most commonly used, is the one for female moulding.   This gelcoat comes in various colours and is unwaxed.   It is usually pre-promoted and, as with resins, will need catalyst added before being applied to the mould surface.  Clear gel coats have an increased resistance to water permeation because they contain no pigments and when backed up by a vinyl ester resin laminate virtually eliminate any possibility of surface blistering known as Osmosis. 

    The type of gelcoat you choose, and the way you apply it, will certainly affect your finished boat. If you are building a male moulded boat, you may well replace the exterior gelcoat with a urethane or epoxy based paint system.