The main consideration when choosing a marine varnish is whether the wood is inert and stable or prone to movement. Marine varnish options include traditional varnish, modern finish and single polyurethanes.
Traditional marine varnish is ideal for wood that is prone to movement, such as carvel planked boat, old clinker and spar. Traditional varnish is easier to apply and remove, but it usually has a longer cure time. It is also high in tung oil content, which results in a golden hue finish when applied.
Modern varnish is harder to remove when recoating, but it resists wear better. It is ideal for a more inert and stable boat, and some brands have strict conditions and temperature requirements when applying it.
Single polyurethanes are hybrids of traditional and modern varnishes, and they have unique advantages, such as shorter cure time due to their reliance on the moisture content of the wood. The finish is also relatively easy to remove, and it allows for several applications in a day because of its optimized cure time.
Using a high quality varnish brush helps to achieve the best result. Brushes with natural bristles such as badger hair work especially well. Users can avoid making brush stroke marks by starting on one section and avoiding going back over the area.