Boat Topside Paint
Topside paint refers to the finish applied on a boat's upper hull and deck areas and always above the waterline. Topside painting is done above the waterline to protect your boat from the sea, sun, and sand. Prolonged sun exposure deteriorates wood and even fiberglass. There are essentially 3 kinds of topside coating: Two part polyurethanes, one part polyurethanes, and enamel paints. Each type of paint has advantages and disadvantages. Deciding which is 'right' for your application depends on your boat's construction and your expectations.
In general, enamels are best on traditional wood boats. As wood swells and contracts, the soft enamel coating flexes with it. However, enamels are not as durable and need an annual maintenance coat. The good news? Soft paint makes it easier to touch up scratches and dings, making maintenance easy. Many enamels are self-leveling, making application a breeze (with a quality brush). Fumes are inert, so these paints can be applied indoors.
One part paints (monourethanes and single part polyurethanes) produce a gloss sheen that is harder than enamel but not quite as durable as two part paints. They are the perfect balance of easy application and hard finish.
Two part polyurethanes yield the most durable, scratch resistant finish. The hardness means it is not flexible, and will crack if not applied to rigid substrate like fiberglass. Polyurethanes produce a high gloss that most closely resembles a factory gelcoat finish. Popular finish coat over tired, crazed fiberglass gelcoat that has first been properly primed with 2-part epoxy primer. Polyurethanes produce a much thinner, almost watery coating compared to enamels, thus require several applications. Best finishes are achieved by roller tipping and spraying. Mix ratios are critical, and produce more wasted paint from unused catalyzed discards. This makes the cost of materials higher.
But only two part polyurethane topsides yield the highest gloss and most durable finish that may hold up as much as five years. Scratch and ding repairs to polyurethanes are visible. Make sure to only apply in well ventilated areas and wear a vapor respirator.
While Non-skid coatings are grouped under topside paints, they are not used on hulls and generally are applied only on decks and other areas where traction is a consideration.