Shop Note
Tung Oil
Michael Koessick
Most so-called "Tung Oils" on the market these days are actually concoctions of
tung oil and something else, usually varnish. If you add heat, they are called
"polymerized oils." (Probably, the most common polymerized oil you come in
contact with every day is the ink in your pen.) There's a at least a couple of
good reasons for using a blend.
- The varnish speeds up drying time. Pure tung oil requires several days
drying time between coats. (A blend, on the other hand, will get tacky in about
an hour.) You gotta have the patience of Job to use the stuff. If you get a
little antsy and put on a second coat too soon, the coat underneath will turn a
whitish color. Once it does that, there's no cure but to take it all down to
bare wood and start over again. Even if you wait the requisite time, you may
end up with that whitish color in the checks and cracks of the wood (between
planks on a ship).
- Blending with varnish gives an extra measure of protection to the wood.
While tung oil is more water resistant than linseed oil, it's not waterproof.
It still allows for water vapor exchange. The varnish makes it much more
waterproof. It also allows you to use less to get the same amount of
protection. Pure tung oil will require about five or six coats to give any
protection at all. You'll get the same amount of protection with about two
coats of blended oil. Also, as you build coats tung oil builds gloss. It's
difficult to control the amount of gloss you get. By the time you have six
coats, which is what you need for any measure of protection at all, on you've
got a right glossy hull. With a blend, because you need to use less, it's much
easier to get a nice, even sheen.
Anyone out there with the romantic notion that pure tung oil is better than
"bastardized" tung oil would do well to remember that tung oil is not
waterproof. You've just finished that beautiful, museum-quality 3000+ hour
model of HMS Rusty Bucket and set it aside while you build a case to protect it
from the elements. Two weeks later you come back, finished case in hand, to
find ugly water splotches all over your creation. I guarantee you'll kick
yourself!
Another thing to be wary of is the softness of an oil finish, whether pure or
blended.
Tung oil is soft and it stays soft forever. Even when blended with varnish,
which will harden it somewhat, it is still soft enough that you can dig a
fingernail into it. So, you'll always have to handle your creation with the
proverbial "kid gloves." (The other side of the coinis that an oil finish is
easy to repair if you ever do dig a nail into it.)
Personally, I wouldn't even consider using pure tung oil on a model - maybe on
a piece of furniture but not on a model. After a six-pack of Guinness
(Brilliant!) I might consider using a blended oil. When I'm stone cold sober,
though, I'll always opt for something more durable - lacquer, pure varnish or
polyurethane. I know that's going to last a while.
Just my two cents worth...
{ Michael Koessick}
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