Old Masters Spar Varnish Spray Clear Oil-Based Spar-Marine Varnish is recommended for use on exterior wood, fiberglass, coated metal, or painted surfaces. It can be used on unfinished wood surfaces or previously finished surfaces. This finish can also be used over stained surfaces that have thoroughly dried. Ideal for use on exterior surfaces, such as fences, railings, lawn furniture, doors, boats, and marine surfaces. For interior use on windowsills and door frames for added ultraviolet protection. DO NOT USE on wooden decks or steps, wood siding, log homes, or wood boats below the water line.