Tung Oil: debunking the myths
Take a closer look at this common finish; there are many things we can all learn about this ancient, and misunderstood, substance.
If you’re a woodworker, I bet you have a strong opinion about tung oil. As a rookie, I became preoccupied (okay, obsessed) with tung oil because I heard so many different opinions about it from veteran woodworkers. Some loved it and some hated it. So I started researching and found that the information available about tung oil was often incorrect, conflicting, and/or misleading. Let’s examine and debunk some of the myths.
Harvest Time
A Paraguayan farmer checks his tung oil crop. Paraguay is second to only China in worldwide tung oil production. (Photo by Blake Hanson)
Big Business
China is by far the world’s largest tung oil producer, providing 83 percent of the world’s supply. (Photo by Blake Hanson)
For Junks
For millennia, China has used tung oil in many ways, including building and waterproofing their traditional boats, called “junks”. (Photo by dreamstime.com)
Tung Oil vs. BLO
To compare the two finishes, Vaughn MacMillan applied boiled linseed oil to the left half and tung oil to the right half of this platter. The tung oil is a bit lighter, and this difference will get more noticeable as time passes. (Photo by Vaughn MacMillan)
Great for Restoration Work
This armoire was in bad condition until it was restored using tung oil. It now has a nice sheen to it and some protection from everyday use. (Photos by Dave Hawksford)
A Nice Finish
For those of you who want wiping varnish instead of a pure oil finish, Waterlox makes one called “Original Finish” that contains real tung oil. This guitar was finished with the Waterlox product. (Photo by Kellie Hawkins)
Myth #1 Tung Oil was invented by Homer Formsby in 1965 (Formsby’s Tung Oil Finish).
Nope. Tung oil has been around for thousands of years. There’s no doubt that Homer Formsby put tung oil on the map in North America in the late 1960s, when he started marketing his special finish. However, according to Bob Flexner in his book, “Flexner on Finishing”, Formsby’s concoction was really a wiping varnish made with (maybe) a little tung oil, a resin and a thinner.
When you buy tung oil, you have to carefully read the ingredients on the package to have an idea what you’re dealing with. I got my hands on several products labelled tung oil that actually contained solvents, and/or metal compounds that speed up polymerization (or drying), and/or other mystery ingredients. Sometimes there was a little tung oil in there too. It’s also possible to buy partially polymerized tung oil, which hardens faster. I’m not criticizing any of those products, but for the purposes of this article I’m referring to pure tung oil with no additives. By the way, Lee Valley was kind enough to send me several samples of the real thing for testing in this article.
The earliest reference I can find to the use of tung oil is in the writings of Confucius around 500 B.C. The Chinese have used tung oil, also known as China wood oil, for at least 2500 years for wood finishing, wood waterproofing, caulking, inks and paints. I also found some references to using tung oil for medicinal purposes in ancient history. I don’t suggest you ingest it or take a bath in it, but apparently some primitive cultures did. In the 13th century, Marco Polo wrote about the Chinese using tung oil to build and waterproof their traditional boats called “junks”.
In 1905, a USDA scientist brought Tung tree seeds to the US to try to cultivate them in Florida. The crop grew well, but bad weather and a succession of hurricanes spelled the end of most of the US production by 1969. Blake Hanson, president of Industrial Oil Products, the only global supplier of tung oil from all sources, told me that there was some US production again from 1998 to 2005 (from his company) until Hurricane Katrina reared her ugly head. Today, world tung oil production comes mostly from China (83 percent), then from Paraguay (about 14 percent), Argentina (2.75 percent), and Brazil (a tiny bit) and it is used in wood finishing, paints, inks, fuels and other things. According to Professor B. Sivasankar, who wrote a recent textbook on engineering chemistry, these drying oils form stable films that protect surfaces from corrosion and weather. This is why tung oil and linseed oil, for example, are essential components in paints. “Without these drying oils, paints cannot function as protective coatings.”
Myth #2 Tung Oil dries in the air by evaporation.
Nope. Tung oil definitely gets hard, but it doesn’t happen by evaporation. Chemists classify oils as “non-drying”, “semi-drying”, and “drying”. The word “drying” is misleading because the oils don’t really “dry” or evaporate; they “harden” or cure.
The most commonly known drying oils in woodworking are tung and linseed oil. They polymerize or solidify by a chemical process that requires oxygen (from the air) to create cross-linked compounds that make the oil get hard little by little, until it is completely hard all the way through.
Myth #3 BLO is just like tung oil, but better and cheaper.
Sorry, but that’s wrong too. Comparing BLO (boiled linseed oil) to (pure) tung oil is like comparing apples to oranges. So let’s look at both:
Linseed oil, which comes from flax seeds, has a long history.
Flax (cloth) fibres have been found from 30,000 years ago, and we know linseed oil was used in oil paints in Europe in the 14th century. Woodworkers have used linseed oil in wood finishes for a long time because it was readily available, flax being grown easily all over the world. Pure linseed oil dries more slowly than pure tung oil, but no one knows that because everyone buys BLO, which dries fast because of all the added chemicals! BLO is definitely cheaper, and it is good; but it’s not better.
Myth #4 Don’t use tung oil on food surfaces (like counters and cutting boards) because it’s risky for people with nut allergies.
Wrong. I heard this information stated adamantly and authoritatively several times in a few different places, but it’s just simply not true.
First, depending on whose statistics you believe, approximately 1 percent of the population in Canada has an allergy to tree nuts. And according to Dr. Gerry Allen, associate professor of biology at the University of Victoria, tung nuts from the tung tree (species Aleurites fordii) are not true tree nuts at all. They are the seeds of the fruit (drupe) like the seed inside a peach pit. So, are allergies to tree seeds as prevalent as allergies to tree nuts? Again, it depends on who you ask, but probably not. The Journal of Allergy and Clinical Immunology says the incidence of allergy to seeds is 0.1 percent in Canada. We also know that allergies to seeds are more common in cultures where the population comes in regular contact with them. Aside from woodworkers, I’d say the general population in North America rarely comes in contact with tung “nuts”, seeds, or oil. So now our risk of allergy to tung oil is down to 0.1 percent of the population.
We know from a study published in the British Medical Journal in 1997 that in a test group with known allergies to tree nuts, none of the test group had a reaction to nut oil that had been refined.
So if tung oil comes from a seed, and if it is unrefined, the probability of an allergic reaction upon exposure is now reduced to 1/10 of 0.1 percent of the population. Is tung oil refined? Sometimes. Blake Hanson told me that often it’s sold as pure unrefined oil but sometimes a solvent extraction (or refining process) is used. So the probability of being allergic to liquid tung oil is now somewhere between 0 and .01 percent of the general population, while the cured hard oil has even less risk.
Myth #5 Tung Oil never dries and you can’t get a good result from it.
Yes it does, and yes you can.
Almost all experts agree that using a cloth moistened with warm water is the easiest way to raise the grain on your project before oiling. This should be done before you apply tung oil. Raise the grain, sand, and then begin. Bob Flexner says that applying oil is simple, “wipe, wait, sand, repeat.” Apply the oil liberally with a soft cloth or brush and then wipe it off like you mean it. Check after an hour or two, and if extra oil has beaded on the surface, wipe it away. Don’t forget that rags used to apply drying oils are highly combustible. When you’re finished with your rag, hang it outside to dry. Be careful disposing of them.
When using pure tung oil, you need several coats. It’s very important that you thin each coat with the first coat being the thinnest (I recommend 70 percent solvent). Each successive coat should be thicker (less thinned), and the last coat must be the thickest. Your thinner needs to be an organic solvent, one that is carbon based like turpentine, mineral spirits or the newfangled “citrus solvent”.
Every layer except the last must be sanded, so the next layer of tung oil will bond to the previous layer. Three hundred and twenty-grit sandpaper creates the “tooth” that grips the next layer. When sanding between coats, you have to go lightly or you will suddenly sand through one or more previous coats and you will have dreaded witness lines.
Getting good results requires using the right techniques and not being in a hurry. I would allow at least a week between coats, although I have heard of people doing it faster with good results. There are many other finishes better suited to a tight schedule; varnishes, lacquers, and even BLO. However, if you want to use oil, and you have some time to devote to the finish, pure tung oil is in a class by itself. There is no other drying oil that has the same resistance to water, mold, bacteria, yellowing, darkening, but offers strength and flexibility.
Well, all that is wonderful, but is tung oil safe? I asked Marc Spaguolo (of internet Wood Whisperer fame and a woodworker with a background in molecular biology) his opinion of tung oil. He said, “It is my belief, that yes it is safe once cured. In general, most of the ‘bad stuff’ in mineral spirits and other petroleum distillates goes away upon evaporation. Any remaining residue can be washed away with soap and water.” He added, “The biggest difference [between BLO and tung oil] is probably cost. BLO is going to be significantly cheaper. But if one is really concerned about chemicals and food safeness, they will be happier with tung oil.”
So let’s recap: tung oil is more expensive than BLO, and it takes longer to dry. The chances of allergy to tung oil are remote, and tung oil has several other advantages over linseed oil. Professor Norm Kenkel, a biologist at the University of Manitoba, reminded me of another reason to use it: “Tung oil is an environmentally safe and sustainable wood finishing product.” There are reasons why tung oil has been used as a wood finish for thousands of years. It’s great stuff. For a traditional pure oil-rubbed finish, it’s the only game in town.
Cynthia White - [email protected]
Cynthia’s table project is dedicated to her shop dog, who died during its completion.
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I use tung oil and have good results with it. I will say I like tung better than any other finish so far. I’m no fan of high gloss coatings and hate polyurethane. I don’t have any need for any plastic like coatings. I like wood done right – that’s stained or natural with a simple waterproof clear coating. A topcoat that will last and pulls out the woods natural colors and wood grain. To date I’ve found nothing that works like tung oil. Most oils I used dry in from two hours to two days depending on the coats and wood when applied right. I have pulled the wood grain out of wood that looked to not have any. With tung oil any wood will look its very best. Don’t spill or drop things on the surface or cover the wood with glass. Tung will deal with the rest.
Hi Carl, loved your article. We installed alder butcher block counters back in oct and have been treating it twice monthly with combination bees wax mixed in mineral oil. It is definitely very dry between coats because within 15 minutes the wood has soaked it up. I would love to use tung oil instead as it sounds like a wonderful product and i would not have to be applying it as often as mineral oil. Is this possible since i have already pre-treated with mineral oil. What would the process be? Looking forward to your reply
I have used real tung oil on a new dining table and it absolutely dries just fine. Have finished three large tables with it over the years. Tops got many many coats of oil and they are practically bomb proof. Never hot a stain on them with years of intense daily use and kids. i dilute with citrus solvent. Smells fantastic. Also, no need at all to sand between coats – you don’t want to sand of what you just applied. Just feed feed feed the wood on first application until it will not absorb what you applied in about 20 minutes. When you reach that point ( or bedtime), wipe off excess thoroughly and repeat the process the next day. Keep going until you find it won’t absorb anymore after a few days. Then you let it sit unused for a full month (in your living area, where it’s warm and dry). Then it’s ready to use. Couldn’t be easier. If you find yourself going on indefinitely, because your wood keeps sucking it up, don’t use any solvent for the following coats. Take a whole day break in between feedings. Makes a gorgeous, velvetty matte finish.
Hello! I’m thinking of making a headboard with a 3/4″ sheet of Oak plywood. And I want a finish that is non-toxic and won’t give off offensive fumes after it dries. Any suggestions? Thanks!
I’d go with a hardwax oil Robert. Low to no-VOCs, easy to apply and touch-up, quite durable. You’ll find more information in my article. Good luck.
Good article! Which 100% pure food safe tung oil you recommend for oiling butcher blocks than can be sourced easily in Canada?
Thank you. It appeared to be oiled finish. Years ago I tried polishing it, not realising, whilst the sideboard looked good, the table never had that finish so I gave up. For years its been just wiped down with a damp cloth, went au naturale. Then I decided to do this. I used a wax and polish remover. Let it dry. Then applied the oil.
I followed instructions which didnt say to remove the excess. I did let it dry, though Im wondering if it wasnt deeper down. Its not in direct sun. I lightly sanded then wiped between coats. Its had 4 coats and now about a been a week since the last. Not happy, I read more and watched videos. The extension leafs excess was wiped off and is much better.
Its brought the grain out beautifully on both pieces and feels very smooth. So Im hoping I get the last leaf correct, not started yet as we are using that end whist the others unfinished.
Will another coat resolve the patchiness? Or do I need to strip it back again?
Personally I’d remove the old finish and start over Rosie.
I’ve applied three coats of Liberon tung oil to a leaf of my dining table, and then started doing the extension leaf. However the leaf is matt, with a mild sheen in parts. Very patchy. I’m not happy with it. I understood from research beforehand that it would have a satin finish.
Does it need longer to dry more? Or should I apply a top coat of something else?
There could be a variety of reasons for the patchy appearance. Did you remove the original finish on the leaf before applying the tung oil? Did you wipe off each tung oil coat between applications. Did you let each coat dry thoroughly between applications – at least a day or two depending on humidity levels? Is the lead out of direct sunlight? What is the finish on the rest of the table? If it’s a different finish than tung oil the final look will most likley be different. When refinishing furniture I typically remove the all the old finish before applying a new finish. Hope this helps.
Hi,
We finally got our swing in our backyard that was build by my wife’s grandfather. It’s made of dark wood (forgot the name). We want to use tung oil for this pretty swing. I’m wondering how many layers of tung oil I should use, and how long I should wait between each layer. Also, how long would it take to dry before we can sit on it? Thank you!!
I would lay on about 3 or 4 coats. Pure tung oil is going to take a long longer to dry than polymerized TO – if you use pure TO allow at least several days between each coat – longer if the humidity is high. PTO will take at least a week to begin to cure (after which youc sit on it) and then a month to fully cure. PTO cures a lot faster.
Pure Tung oil definitely hardens. I bought a gallon about 10 years ago when exploring ideas for a non toxic finish for my wood flooring business. Turned out it’s not really practical for wood floors in it’s raw state. Since then I have used it for many outdoor projects like fenceposts, garden gates, planter boxes etc. It’s the best outdoor protectant Ive come across and has a prodigious shelf life. The only issue, other than drying time, is a strong (yet unoffensive to me) nutty odor that never seems to completely go away. I just use it, rain or shine and it does it’s thing, even after being rained on hard immediately after application. I was pleasantly surprised about that last quality. Personaly. I think it’s a highly under used natural product that big money definitely has an interest in keeping on the down low.
Use Odie’s Oil, it is Tung Oil based but vastly improved with the addition of other natural ingredients. It protects better than plain oil Tung Oil, it waterproofs, never fades, yellows, peels, flakes, or chips off because it hardens INSIDE the wood surface. I use it for everything from wood to cement, leather, stone, terracotta, and plastics. Incredible water proofing and yet the surface is natural to the touch and looks absolutely amazing. I’ve used it for over ten years now and every project still looks like brand new.
Is pure turpentine food safe to use as a thinner for pure tung oil to treat garden beds?
Hi Richard. My understanding is that pure turpentine is mildly toxic when directly consumed (pure tung oil is non-toxic when cured). I assume you are referring to a finish for raised garden beds. I’ve no experience using turpentine and tung oil on exterior wood. I’d opt for a product specifically designed for outdoor applications that is waterproof and UV reactant. The one I’ve used for a number of years is Rubio Monocoat’s hybrid wood protector, which is made of linseed oil and wax. All the best.
I’ve not used Tung oil for a butcher block – I find that it takes too long to cure. A product I’ve had good success with is Osmo Clear TopOil (https://osmo.ca) which you can get at Lee Valley (https://www.leevalley.com). Hope this helps.
What Tung Oil brand name do you suggest I buy for making a butcher block on new hard wood.
Hi, can you comment on using Tung oil on Cedar exterior sidings? We like it being a natural product, but it seems to encourage fungus growth faster than synthetic product. Is there a way to avoid it? Thanks!
I’m new to making my own raised garden and have looked into linseed oil vs tung oil to finish the wood I’m using in my beds. I’m leaning toward tung oil and wonder how many coats you’d recommend. Also, a friend is offering to give us newly milled wood that hasn’t been dried. Would that work, or would I have issues with warping? And can you use tung oil on wood that’s not been dried. I’d appreciate any help you could give me.
Hi! In myth #5 you talk about thinning the tung oil in each coat. Can you please give me the ratios for each coat.. I have a birch butcher block countertop. Can you send me step by step instructions in how to apply this? Also on sanding between coats… what grit and how do I know if I sand too much?? Is this just a quick very light sand? thank you!
See myth #5. If your tung oil is not drying you have: Applied it too thickly; not waited long enough; are not using real tung oil. Unfortunately, at least in the United States, a manufacture can call something tung oil with out much actual tung oil in it. Boiled tung oil will cure more quickly.
Cynthia, appreciate your insights into the mysteries of tung oil. I have only used it a few times on small projects with new wood. Now I am considering using it on two teak dining chairs I am refinishing. They are of excellent quality, both in the wood and the construction. They are a little over 10 years old and have been stripped and re-teak oiled 3 times. I have thoroughly cleaned, stripped all old oil (at least the vast majority of it) and have spent four days sanding the two chairs. I now plan to use an aniline dye on them. What dilution ratio would you recommend starting out with? I was thinking of 3 to 1 (solvent to oil) And, until I read your most recent column, I had planned on using a “new-fangled ‘citrus solvent'” as recommended by the manufacturer. Any reason not too, other than “new fangled-ness”? Appreciate any guidance or suggestions you can provide. I am looking forward to reading your thoughts.
Hello Cynthia. I am writing for some advice / opinion. I am refinishing a 6 legged 90 year old wooden table, about 33″ (L) x 20″ (W) x 30″ (H) in a roughly oval shape. The top surface is of veneer with a rectangular 1/4″ inlay in the surface with veneer on both sides. I’m looking for the best way to refinish the surface once all the sanding and prep work is done. I have come across this article by yourself and I wonder if TUNG oil is suitable for this purpose on the top, and also for the turned legs (solid) and lower shelf.
Hi Norman. You don’t want to use raw tung oil – it will never dry. What you could use is a polymerized tung oil (available from Lee Valley). It’s very easy to apply, dries reasonably quickly, and gives good protection. Hope this helps, Carl