It doesn't come from teak, and teak is already oily enough without it, but teak oil has a place in the hearts and paint cupboards of many woodworkers. Its actual composition is a secret -- one leading manufacturer lists only solvents in its product ingredient disclosures. Aficionados note that teak oil is thinner than other finishing oils, making it the perfect finish for dense, oily woods, such as mahogany, rosewood and -- yes -- teak.
Only two true finishing oils occur naturally. The first is linseed oil, which is derived from flaxseed and "boiled" by combining it with chemicals to speed its drying characteristics. The second is tung oil, which comes from the nuts of the tung tree. These oils are typically applied full strength, and they soak into the wood and harden in the grain to provide a degree of water and impact resistance. To improve the penetrability of these oils, manufacturers combine them with solvents, which is how they make teak oil.
A Wiping Varnish
Technically, teak oil isn't a true finishing oil, but a wiping varnish. Besides tung and linseed oil, it often contains a resin, which might be alkyd derived from plants or a synthetic plastic, such as polyurethane. Besides its oil-to-solvent ratio and the composition of its oils, teak oil differs from Danish oil and other compound oil finishes in the amount of resin it contains. Danish oil typically contain more resin than teak oil, which makes the resultant finish glossier and a little harder. Because manufacturers aren't required to disclose all the ingredients, you seldom know the exact composition of the product you're using.
Using Teak Oil
As is true whenever you're applying a finish to wood, the surface must be clean. It's always a good idea to sand just before application of the oil; this removes deteriorated wood cells from the surface and opens the grain, allowing the finish to penetrate more deeply.
Strip any existing finish with chemical strippers or solvents. Rough-sand with 100-grit sandpaper to remove stripper residue; then fine-sand with 120- and 150-grit paper to prepare the wood for finishing. The final sanding should be done by hand, using 150-grit paper and going with the grain of the wood.
Apply teak oil liberally with a rag or a paintbrush. Wipe it into the grain, using strokes that are parallel to the grain, and let it soak in. Apply more to areas that soak it up.
Wait for about 30 minutes; then apply more oil in the same way.
Wipe the surface dry after 15 minutes, and let the oil dry for 8 to 10 hours.
Apply a third coat, if you're looking for the smoothest surface finish possible. Scuff the wood with 220-grit sandpaper to smooth the grain; then wipe off sanding dust with a damp rag and apply the oil liberally. Wait 15 minutes, wipe off the excess and give the oil an additional 8 to 10 hours to dry.