Q. My house has some beautiful old woodwork, which I need to sand and refinish. I was thinking of using a natural oil finish on it. Is this type of finish durable? And how should I apply it to the wood?
A natural oil finish should be good for your old woodwork because that likely is the type of finish it originally had. A hand-applied oil finish is particularly attractive because it creates a very soft natural appearance and feel to the touch. It gives the surface a sense of depth, which is difficult to match with other wood finishes.
An oil finish is not going to be as durable as a urethane or other polymer finish. It will not resist water and food stains well, and you cannot get a gloss or even a semigloss appearance with it. Other than its attractive appearance, the primary advantage of an oil finish is it is easy to repair if the wood gets scratched. Just sand out the scratch and apply more oil.
It helps to understand how an oil finish cures so you know how to apply it. It does not technically “dry.” Two finishing common oils, tung and linseed, absorb oxygen into the oil surface. This can take from hours to days depending upon the type of oil. Boiled linseed oil cures faster than raw linseed oil because drying compounds are added to it.
This oil/oxygen combination decomposes, producing compounds that react with other fatty acid molecules. As they react together, they form stable chemical bonds and become a polymeric surface finish.
Raw linseed and boiled linseed oil are the most commonly used oil finishes. This is because they are inexpensive and easy to work with. As the finish on the wood ages, it will darken slightly. This is an advantage if you desire an antique appearance or you feel the natural wood color is too light.
Tung oil is more expensive, but not excessively so. It can be found at most paint stores. It produces a somewhat more durable finish than linseed oil, and it does not darken the wood as much as linseed oil.
Walnut oil is an excellent finishing oil, but it is considerably more expensive than the above two oils. It dries very slowly, but it will not change the color of the wood. To find it in its most pure form, purchase it in the edible oil area at your supermarket.
The key to an attractive oil finish on wood, as it is with almost any wood finish, is the initial preparation of the wood surface. Oil is more sensitive to fine scratch marks in the wood because it does not bridge them as well as some other finishes that are applied heavier, in fewer coats.
A machine sander can be used for the first pass. With curved surfaces, you have no choice but to hand sand from the start. If you can machine sand, use P180-grit sandpaper, followed with 180- and 220-grit garnet hand sanding. You may also burnish the surface with 400-grit sandpaper.
Liberally apply the oil, and give it 30 minutes or so to soak into the wood. Wipe off the excess. Allow it to dry overnight, and lightly buff the surface. Apply three more coats similarly.
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