Is It Possible To Apply Outdoor Polyurethane Inside?

Polyurethane is a durable varnish that comes in microscopic chains of resin molecules that adhere together once the product dries. It is more abrasion-resistant, solvent-resistant, and water-resistant than other vanishes. Exterior polyurethane is great for protecting wood that can handle weather, sun, and moisture well. It can be used for outdoor furniture, decks, and doors. However, it should not be used outside as it has resin that absorbs ultraviolet rays, while interior poly doesn’t.

There are different formulations of polyurethane, with water-based polyurethane being ideal for indoor use on pieces like nightstands, desks, photo frames, and coat racks. However, when applied indoors, the product tends to acquire a whitish look. The exception is the use of Minwax Helmsman Spar Urethane, which is a protective clear finish for exterior or interior wood exposed to sunlight, water, or temperature.

For interior projects, both oil-based and water-based polyurethanes are suitable. However, for exterior use, the product will stop smelling once the finish fully cures, which happens faster in a warm environment. Regular PU is not well-suited to the outdoors because it has no UV degradation inhibitors, so eventually the sun will eat it.

Indoor varnish can be used outside if you are willing to refinish more often, but it won’t be as happy with sunlight or wide open spaces. Circa 1850 Exterior Varnish is safe for all interior woodwork, and it is recommended to let the exterior stains sit longer to ensure they are completely dry before sticking inside a house.