How to... Paint over gelcoat
Q
We recently purchased a 1999 Wayfarer World, which has over the years acquired quite bad UV discolouration along the port side and the stern. We have taken a lot of advice most of which has been contradictory.
Enquiring of chandlers and purveyors of proprietary gelcoat restoration products, the main thrust of their advice has been a chemical remedy, cutting back using various agents and waxing. On the other hand, a local boatbuilder with over four decades’ experience advises us to use a two-component polyurethane paint, saying that it will outlast by far any chemical cutting compound solution.
Our aim is to restore the hull by whatever means and sell the craft in favour of purchasing a larger vessel. The photos show pretty clearly the extent of the UV damage. Keith Willis, Bristol
RICHARD JERRAM REPLIES:
Using polishing compound is a short term remedy, while applying a two-component polyurethane would be a more long-term solution.
In preparation for painting, the hull should be thoroughly washed with a degreasing agent to remove all dirt and polishes. It’s important all dirt and contamination is removed to ensure good adhesion of the two-component polyurethane. The hull will then require sanding with a 280-grade abrasive to achieve a matt finish. Wash down thoroughly to remove all sanding debris.
You then need to apply two or three coats of either a two-component polyurethane undercoat or an epoxy primer as a basecoat. When the undercoat/primer has fully cured (approximately two days) abrade back using a 280/320 grade abrasive. It’s important to ensure all brush marks are removed so they do not show up when the finishing coats are applied.
Apply a minimum two coats of a polyurethane using a foam roller and then tip off with a soft-ended paint brush (the end of the bristles should have a split end appearance). Apply about a 45cm (18in) band and then lay off into the wet edge. As the solvents in the paints are quite strong the foam rollers will soften during application so make sure you have plenty of spares. Also avoid painting in direct sunlight as this will cause the paint to dry quickly without giving brush marks a chance to flow out.
See also: pbo.co.uk/ expert-advice/paint-boatlike-new