THE LIES AND CONFUSION OF TUNG OIL WOOD FINISH

When I was growing up, my grandparents owned a small country hardware store. I worked there as a teen and my 20s. Needless to say, I have a lot of memories from those days, including an old woodworker who would come in to buy tung oil. He spoke of it like it was an elixir of the gods—the perfect finish. Even today, I hear folks speak with reverence about tung oil.

What they don’t realize is that they’ve been lied to. We didn’t sell tung oil in our hardware store. The bottle may have said “tung oil,” but it was full of more marketing than pure oil—just as our bottles of Danish oil had no connection to Denmark. Of course, we didn’t know it at the time. We’d been lied to as well. We’ve all been duped.

There is more confusion and nonsense surrounding tung oil finishes than perhaps any other finish out there. This matters because tung oil can be one of the most beautiful natural wood finishes around. But slick marketing has confused so many people that you hear wildly contradictory claims about the proper way to apply it, how long you must wait between coats, and whether it’s even the right finish for your project.

In this article, I’ll sort through the myths and the marketing. I’ll help you identify what’s actually in your can, whether it’s the right finish for your project, and how to properly apply it.

What is Tung Oil, Really?

First, let’s identify what tung oil actually is.

Pure tung oil is made from the nuts of the tung tree, which doesn’t hurt the tree at all. Tung trees are found in Asia and South America, and the oil has been used as a wood finish for thousands of years.

It remains popular today because, in its pure form, tung oil is more durable than some other natural finishes, like linseed oil. It does add a slight amber hue to light-colored wood, but it doesn’t darken over time or go rancid like linseed oil might. It’s food safe, water-resistant, eco-friendly, and doesn’t put off harmful fumes. Pure tung oil is one of the most beautiful natural wood finishes around. No wonder it’s a favorite of both old-timers and new woodworkers alike.

But there are some downsides to a pure tung oil finish. For one thing, it’s pretty thick—almost like honey. It soaks into the wood fibers slowly. It also dries very slowly, requiring a great deal of time between coats. Like linseed oil, a pure tung oil finish also needs to be maintained through regular reapplication every few months, or it will look dull and dingy.

If you think this sounds like a lot of work, you’re not alone. That’s why many tung oil products contain only a small percentage of pure tung oil—perhaps 5% or less by volume. The rest of the can is a blend of solvents to make it easier to apply, drying agents to reduce the time between coats, and resins to make it more durable, glossy, and easier to maintain. Some tung oil blends don’t even have actual tung oil in them.

But all these blends are still often labeled as “tung oil.” So, one person’s tung oil finish may be different from another person’s, even though they are generically referred to by the same name. This causes a lot of confusion and contradictory information.

How Can You Make Sense of What’s in Your Can?

Pure tung oil will say it’s pure right on the label. It won’t have a bunch of mystery ingredients. The label won’t say things like “contains petroleum distillates” or “aliphatic hydrocarbons.” It won’t come in high gloss or medium gloss because pure tung oil is a low-gloss finish.

Don’t get me wrong—I’m not saying these blends aren’t good finishes. Petroleum distillates are thinners that may make the finish easier to wipe on with a cloth and help it soak deeper into the wood. Metal or chemical driers, or partial polymerization, help it dry faster. Resins can provide a higher luster if that’s what you’re looking for. They may also make the finish more durable for projects that will see some wear, like tabletops. But some people feel those resins mute the beauty and figure of the wood.

The bottom line is that you need to know what’s in your can so you can make an informed decision about whether you want to use it on your project and how to apply it. Because that’s another subject of confusion.

One person may tell you to wipe it on right from the bottle. Another may tell you to thin it with mineral spirits first. You may be told you can recoat in an hour or so, or that you must wait several days between coats. Some claim you can’t build up a tung oil finish through many layers, while others claim you can.

Why So Much Confusion?

Again, it comes down to what’s in the can. Everyone thinks they’re applying the same tung oil finish as the next guy, and they assume the other person’s methods are wrong. But the truth is, they may be applying totally different finishes with totally different requirements.

To sort this out, I’ll walk you through how I put tung oil finish on wood.

The Application Process

First, I like to raise the grain by wiping it with a damp cloth. When it’s dry, I lightly sand it smooth again.

Pure Tung Oil Finish

In this example I’ve applied pure tung oil because that’s the most challenging variety.

All tung oil finishes can be applied with a brush or a cloth. Since pure tung oil is so thick, I find a brush is less messy.

Whether it’s pure or a blend, you want to flood it on liberally and give the wood time to soak it in. I watch for dry spots to appear and add a little more. This first coat may take several minutes to fully saturate the wood. When it doesn’t appear to be soaking in anymore, I wipe off the excess and let it sit.

Blended tung oil finishes are much thinner, so they soak in faster and perhaps deeper into the surface fibers. This is a good thing because the deeper the penetration, the better the protection. You can get this same effect from the pure stuff by thinning it about 50% with turpentine, mineral spirits, white spirits, or even pure orange oil if you don’t have access to petroleum-based solvents.

How Long Should You Wait to Re-coat?

That depends on the blend. And again, this can get confusing. Many blends say to wait about 12 hours to recoat. They actually contain as much as 80% mineral spirits, which evaporate very quickly. Those 12 hours are required for the added varnish resins to dry, not for the tung oil, which only makes up about 5% of the can.

Pure tung oil dries very slowly because it must react with the oxygen in the air and harden, rather than evaporating. When I learned to use pure tung oil, I was taught to keep flooding the wood until it wouldn’t take any more. Wipe off the excess and then wait at least three days for it to harden before adding a second coat.

So why do bottles of pure tung oil typically say to recoat after just an hour? Because they aren’t talking about adding coats in layers to build up a protective film. They’re talking about waiting an hour for the first coat to soak in, then adding more to it until the fibers are fully saturated.

It’s not contradictory, it’s just confusing. They are describing a multi-step process of applying what really should be called the first coat. If you apply more after just an hour, you’re merely adding to that first coat. The new oil will just mix with the hour-old oil.

Think of it like adding water to a sponge. You put some water on top and let it soak in, then you add some more and the sponge gets more and more saturated. You wouldn’t call that adding three coats of water to the sponge. You’re merely incrementally soaking the sponge. Yet this bottle makes it seem like layering on coats rather than soaking the fibers.

The Real-World Application

I took some time to make sure that first coat was fully soaked in, adding more as needed and wiping off the excess laying on the surface. Then, I let it sit overnight.

The next day, it was not fully dry—not the side that was pure tung oil, nor the side that I thinned 50%. It looked mostly dry, even felt dry. But it wasn’t dry—it just fully soaked into the wood. I know it didn’t dry because my cloth, which I hung up overnight, was just as damp as the night before.

Tung oil does not dry in one hour, two hours, twelve hours, or even twenty-four hours. It will take days. How many days depends on how thin the coat is. Thinner coats dry faster because the oxygen in the air can permeate through it more quickly. You may be able to recoat after three or four days if you applied a 50% mix of oil and thinner. It may take as long as a week for a thick coat of pure oil to dry.

If you use blended finish with just a little tung oil in it, you’d be ready for another coat after just a few hours.

Re-coating and Building Layers

Whatever you’re using, when it’s time to recoat, you should first lightly sand with about 300-grit paper. This will smooth out any surface imperfections and create a mechanical bond between this layer and the next.

After that first coat, successive coats won’t soak in nearly as much because most of the pores were filled by the first coat.

Keep repeating this process for as many coats as you wish to apply. Wipe, wait, sand, wipe, wait, sand, and so on.

Don’t rush it. If your sandpaper gums up, it isn’t ready to recoat. Rushing a pure tung oil finish will lead to something that looks like wrinkles as the finish puckers and raises.

How Many Coats Do You Need? I like a lot of them—perhaps five to seven or more.

Conclusion

Is a pure tung oil finish worth the effort? Maybe, maybe not. Some people aren’t in a hurry, they like all-natural finishes, and they see a special beauty in a well-built-up tung oil finish. Others are eager to get things done. The latter greatly outnumber the former, which is why there are so many blended tung oil finishes available.

It’s up to you to decide which is best. I hope this clears up some of the confusion you may have about tung oil finishes. Happy woodworking!

Sorting through the mess of contradictory information about what should be a simple subject

Pure tung oil: https://amzn.to/3ay0KXA

Formby's tung oil blend: https://amzn.to/3oMQ2Bl

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