Tung oil is an ancient form of wood sealant that comes from the oil of the tung tree. The tung tree originated in China, and the oil has been used for years to seal and protect wood. Urethane wood sealers are typically made from petroleum products and offer a tougher seal than the all-natural tung oil. While urethane is sometimes used to add additional protection over tung oil, tung oil is not compatible over urethane coatings.
Tung oil is a natural wood sealant. When rubbed into the unfinished surface of a piece of wood, the oil sinks deep into the pores of the wood, sealing them from water and other potentially damaging exposures. Within a few hours, the oil dries to a hard finish. Typically three or more coats of oil are applied to the surface of a floor or furniture piece to create a barrier from the elements. Modern tung oil finishes will sometimes have the addition of polymers that speed up the drying time for the oil, or polymers that are designed to make the finish stronger.
Applying Tung Oil
The process of applying tung oil starts with fresh, sealant-free, sanded wood. Usually tung oil is applied to bare wood with a soft cloth. Use a liberal amount. Allow the oil to sit for about 10 minutes before blending into the surface of the wood. The oil is wiped into the surface of the wood and the remaining oil is wiped away. Coats are allowed to dry for several hours between coats. Drying time varies, depending on the form of tung oil used.
Tung Oil and Urethane
Tung oil bonds with the pores of the wood. If a urethane sealant is already present on the surface of the wood, the tung oil has nothing to bind to. While the tung oil might still harden, the finish will easily flake off, leaving an unsightly, cloudy surface. Urethane also bonds inside the pores of the wood, which makes the application of two separate coatings completely unnecessary. Typically urethane coatings are used for high-use applications, such as for floor sealers.
Urethane Over Tung Oil
Urethane coatings can be applied over tung oil applications. Urethane bonds better with smooth surfaces than tung oil. Some people prefer to add a urethane coating over their tung finishes for additional protection. Urethane sealers are often added over countertops to prevent the tung oil from flavoring food prepared on the surface. Urethane is also more heat-resistant, which is ideal in kitchens.