This marine-quality finish remains flexible and will expand and contract to outperform traditional polyurethane varnishes. Woodcare Marine Spar Varnish provides a durable, U.V. weather resistant finish, making it an ideal choice for exterior wood doors, window sills and trim. Use on bare, stained or previously varnished interior and exterior wood surfaces including doors and trim, outdoor furniture, fencing, railings and wooden boats. Use on bare, stained or previously varnished or finished surfaces.