How Does Tung Oil Work?

A little basic information on Tung oil. March 28, 2010

I use tung oil for various projects, but I have a little trouble understanding its application. It's not easy to understand like an evaporative finish. Most of the time, I brush on a thinned out heavy coat of polymerized tung oil, rub it pretty thoroughly with a grey synthetic steel wool pad (by hand or attached to a Harbor Freight jitterbug orbital sander I bought for the purpose), then wipe it off entirely. The next two to five coats I do the same, but with a less thinned out finish. The final coats, I double check my wipe down after 15 minutes in case something's coming out of a pore or I left a thumb print.

If I wipe it down, how am I getting build, if any? Does the finish get absorbed into the previous coats? Are extra coats not really doing anything but helping to burnish the wood with all that constant rubbing? Should I just burnish one or two coats and call it a day?
Thanks for any help!

Forum Responses
(Finishing Forum)
From contributor D:
Generally Tung oil and BLO cure/dry by oxidation. One or two coats would provide some protection but the real beauty of a traditional oil finish does not begin to show up until you are at least five coats deep. The general rule of thumb is sand with 220 prior to each except the last two, before each of these caots sand with 320. They both make wonderful finished products and when buffed out are beautiful and do a lot to accentuate the natural beauty of the wood. The downside is, depending on temperature, a coat can take 24 hours to cure. Why not use a product with Tung oil in it? Waterlox is a terrific finish and will cut you dry time down some. It builds nicely and is very resistant to most any type of household chemical.

From the original questioner:
Should I not be wiping off the oil, as all directions tell me to?

From contributor D:

Let the oil soak for a few minutes and then wipe off the excess.

From contributor W:
Tung oil goes through an oxidation/polymerization process as it cures at that takes time - days at least. In early coats you must be careful to wipe it down frequently or risk blisters of cured finish.

Polymerized tung is pre-polymerized by heating it to high temperature in an oxygen free environment. Since it is pre-polymerized it does not required the days or even weeks of curing time that tung oil does. In fact you can recoat polymerized oil in two hours or less. Its short working time is the reason it is usually restricted to smaller pieces or projects.

If you want to fill the grain a little you can sand your first couple of applications with very fine wet or dry paper, or just rub the finish in until it begins to tack. Wipe off the excess but not too vigorously. Then apply additional thin coats without wiping. After five or six coats you should see a nice build. Let it set for a week or so and then rub it out.