How do I stop my dark blue gel coat from going chalky
An application of a rubbing compound will remove the white chalking, but it is actually removing the thin film of resin that has oxidised. This is not a sustainable solution as it will eventually rub the gel coat away entirely. Some dark coloured hulls such as the Fairline Targas have a feature colour to the flanks and white to the hull below the chine. This is achieved by spraying a thin coat of coloured gel into a masked up mould, which is then unmasked before the full thickness white gel is applied to all the mould. Many owners have found that by regularly compounding the white chalking, eventually the chalky patches they are rubbing are actually the white gel coat showing through. This also applies to topsides with broad coloured sheerline stripes such as Etap and Westerly.
The only effective solution is to polish the gel coat after compounding with a good polish. Wax-based products are widely used on gel coats but appear to give better protection than they actually do. Carnauba waxes provide protection from photo-oxidisation, however they give very limited protection from photoinitiation or UV attack. UV protection with carnauba wax begins to drop off in about 50 hours of exposure, with an almost total loss of protection after 250 hours.
The best method for resisting UV attack is to apply a UV resistant surface coating. Silicone waxes are UV resistant but the problem with silicone compounds is that they tend to migrate. Because they are difficult to bond, they tend to move to adjacent surfaces and into porous materials such as the polyester gel coat film. This can cause serious problems with subsequent bonding in the event of the gel needing repair or refinishing. There is also the possibility that silicone migration can cause embrittlement of the gel coat increasing the risk of crazing. Polishes containing PTFE, sometimes referred to on imported products as PTEF, provide the same protection as silicones but have none of the problems associated with it.