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Depending on what you're reading, tung oil cures in a day

I use Minwax tung oil on all my turningings. Two Coats ussually. After the second coat, I buff with the Beall Buffing system, Ussually about 6 to 24 hours after applying last coat of tung oil.

a few days:

... tung oil is too difficult for most people to use by itself as a finish. You apply tung oil just like linseed oil or oil/varnish blend, but you have to sand tung oil after every coat, not just after the first, and it takes five to seven coats, allowing two to three days drying time between each, to achieve a smooth, attractive sheen.

or several weeks:

Depends... true 100% pure tung oil needs about 2 weeks to cure... why do they sell this stuff as a finish?

What's the real story behind tung oil curing time?  How long do I have to wait between coats?

  • I've recently finished a couple large projects with tung oil and wanted to add to what's been written. Really real tung oil is less of a coating and more of a wood treatment. Don't expect it to look like a poly coat just because it's a polymer. It saturates the wood and becomes part of it. It should NOT sit on top. Definitely add more oil as it soaks in until the wood is entirely saturated, then start wiping off any residue that seeps out every fifteen minutes for the next hour or two. I do that for each coat and about five coats of 50/50 tung/pine oil (to thin) gives me a result I love. The f – Portend Jan 6 '18 at 19:44
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TL;DR In general, I would avoid turning to discussion forums when trying to find advice about tung oil as it’s very likely the person talking has innocently confused the product that they are using.  If you do enough research you will eventually find contradictory information about everything.  (if only there were a place where people could vote on different perspectives and a consensus could be built from our collective experiences!)

Due to the unclear and deceptive labeling, the best practice when using a tung oil product is to allow yourself the time to experiment with scrap first, and follow the instructions on the label.


Explanation

Some of the confusion comes from the fact that you don’t have to wait for a complete cure to apply additional coats.  However, the primary reason there is so much conflicting advice is that they are so many different types of products labeled as “Tung Oil”. There are the three major varieties:

Pure, Unadulterated Tung Oil

Probably the least common variation, pure, unadulterated tung oil is the most difficult to work with (that’s why the other variations are so common). It doesn’t penetrate into the wood as well as the others and takes longest to cure.

A full cure can take 15 - 30 days, depending on the nature of the application and the temperature, humidity, and air circulation of the curing atmosphere. However, you only need to wait one or two days between coats.

Modified or Polymerized Tung Oil

Because pure, unadulterated tung oil takes so long to cure and has poor penetrating properties, many companies sell tung oil that has been heated to encourage polymerization. Depending on for how long its been heated, the result may too thick to work with and so polymerized tung oil is often mixed with solvents by the manufacturer to aid penetration and workability.  Probably there are varieties out there that have solvents but haven’t been polymerized. Depending on the solvent, modified tung oil may not be food-safe like pure tung oil.

Note that even products labeled as “pure” tung oil can be polymerized and have different drying and penetrating behavior than pure, unadulterated tung oil.

The time between coats depends on the formula and amount of heating done by the manufacturer. You’re best bet is to follow the times listed on the can.

Complete Impostors

Many products labeled “Tung Oil Finish” are actually more like a wiping varnish than an oil. In my experience, these are often the only variety sold in the Big Box home improvement stores. They leave a finish that resembles tung oil but you’ll often read people complaining that they have no tung oil at all. Only the manufacturers know for sure because tung oil is not hazardous and therefore doesn’t need to be reported on an MSDS. They have much different food-safe and water-protection properties than tung oil.

Again, the curing time and time between coats for these products will depend on what the manufacturer uses. A good first approximation should be listed in the instructions on the can.

  • 2
    This is a good response. Most of my knowledge comes from Bob Flexner (two books and an ongoing column in Popular Woodworking magazine) who says the same. He lists Homer Formby's Tung Oil Finish as one which actually has no or only trace amounts of actual tung oil in it. I suspect MinWax is the same; which is not to say that those finishes are not good; I've used MinWax products before and been happy with the results. And, in response to the OP, in such cases I let it cure for 24 hours. – glw Mar 30 '15 at 16:09
  • Good answer and gave me a lot of clarity. What I thought was tung oil was actually minwax "tung oil protective finish". That's not to say this finish isn't useful - it's actually done a great job on some old pieces where I wanted the old, chipped paint/stain to remain visible to show its age & character, ie the sort of thing a wiping varnish is good for. I'll pick up some oil for my next project that actually needs oil, but now that I know what to look for BLO is starting to sound like the much easier option. – Josh from Qaribou Nov 7 '17 at 9:05
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What's the real story behind tung oil curing time?

Like all things in this area there are complications and potential for confusion. As already covered, many tung oil products on the market aren't tung oil to begin with.

Where you are talking about actual tung oil, there are then various types. The product container may not specify how, or even if, the oil has been modified to improve drying. You might guess it has if it has a short drying time listed, but there are still unknowables.

How long do I have to wait between coats?

This is the key part of your questions I guess — to a degree it doesn't matter what you're using, you just care about when you can re-coat. And the answer to that is unfortunately, it depends.

Obviously it depends on the product, for the reasons listed previously.

But local conditions play a huge part in drying times. At higher temperatures and lower humidities most finishes dry (and then cure) faster, ay lower temperatures and higher humidities drying and curing are retarded. And at very low temperatures proper drying may not occur at all. because of this many products have a minimum usage temperature listed which users should pay attention to.

2

NOTE: This advice refers to finishing smaller projects with relatively small surface area, like bokkens (wooden training weapons). Tung oil is one of the best choices for these, however, that's not always the case in other applications, like large furniture (unless you know what you're doing).

From my experience with pure tung oil, if you treat it like every other finish and just let it sit, it will never cure. No, literally never. The only way for pure tung oil to cure in a realistic time-frame is to optimize your curing environment.

Factors that determine the curing speed are humidity, temperature, coat thickness, and most importantly, number of air changes per hour. If the temperature is below 50 degrees, don't bother. 70 is acceptable, 90+ is best. Humidity in the curing environment shouldn't exceed 30%, the less the better. Higher humidity means more water and less oxygen in the same amount of air—and likewise—drier air means more oxygen can form long chains with the oil, which is how tung oil cures.

Let's cover the number of air changes per hour. Simply put, it's the number of times all the air in the interior gets replaced with new air (within an hour). The more fresh air enters and mixes with the curing air, the more oxygen is delivered to the oil.

It is the most crucial factor, since even if your humidity is at 5%, but there is no air-flow coming in, the oil will just sit there and wait for you to remedy the problem, while you're waiting for it to cure.

The last factor but no less important is your coat thickness. With tung oil it's simple—more thin coats is much better than less thicker coats. In a thick coat, oxygen can't reach all of the oil, and the surface will forever feel rubbery and very sticky. Be sure to wipe off the excess oil no more than 10 minutes after applying the coat. Some people wait 30min, some as long as an hour. It's a big mistake that leaves the oil beneath the surface unable to cure (as with thick coats), and renders your finish ruined.

First time I was using pure tung oil, I had an open window, but no forced air-flow. I also applied too thick coats of oil, and waited too long before wiping off the excess. I waited 6 weeks for one coat to cure, and it never did. Next time, in addition to applying thin coats well rubbed into the wood, I put a cheap 9" fan in that same window, blowing fresh air directly onto my project, and each of my tung oil coats cured within 4-5 days, which for pure tung oil truly is the speed of light. Thanks to the forced flow of fresh air, my number of air changes per hour increased dramatically, as opposed to no air-flow. For the same reason, the smaller the interior you're curing tung oil in, the less air needs to be replaced, and the faster the curing.

As for "how long till I can re-coat?", pure tung oil requires that each coat be completely cured before you can re-apply the oil. There are no shortcuts and no "minimal curing time". How to tell if it's cured?

There are a few behaviors the finish has to display.

First, the finish cannot feel sticky to the hand, at all, whatsoever. If it does, the oil isn't done reacting with oxygen. You can perform a "tissue test", where you firmly press a tissue against the finish with your finger, then slowly pull it away. If any tissue fibers get caught in the oil, you know it's nowhere near being cured. Also, there can be no oil odor on your hand after touching the finish, and no odor on the cloth after briskly rubbing the finish. All those behaviors will occur in this order as the oil continues to cure. Ultimately, only when there is NO detectable oil odor once you smell the finish up close and there's absolutely no sticky feel to the surface, the finish is ready for another coat. When oiling bokkens, I leave it for another 24-48h after there's no detectable smell.

Experiment, examine your results and see what can be improved in your tung oil application process next time around. And remember not to give up! Dealing with tung oil is like taking care of a 2-weeks-old kitten, but it's the best wood finish (for wooden weapons) and well worth it.

  • 1
    "it's the best wood finish" Err, really? This kind of thing is of course subjective but the extremely finicky conditions you just outlined yourself would give me some pause just by themselves. But in addition it imparts minimal waterproofing, can't provide a high gloss (either at all or in a reasonable timeframe) and imparts almost no scratch resistance..... that sure doesn't meet my standards for "best finish". – Graphus Jun 17 '17 at 7:16
  • That of course can be true, depending on the application, as in what do you use it/need it for. In my case, I use it to finish bokkens (Japanese martial arts training swords) made of hickory, and for that tung is one of the best choices due to semi-smooth tactile feel and perfectly sufficient water resistance, as well as flexibility and behavior on impact with other wooden swords. The name of the game is what finish best suits your needs, I guess I should have specified mine. So I can perfectly understand it can be not worth the pain if you need to finish a large dresser. – Dr.U Jun 17 '17 at 16:04
  • This makes me wonder what my bokken and nunchakus where finished with :-) – Graphus Jun 18 '17 at 7:11
  • In 90% of production wooden weapons it's varnish. Some places use teak oil, like Kingfisher Woodworks, but it requires reapplying quite often, not as often as lemon/walnut oil. I've never seen production pieces finished with tung oil, mostly people who make weapons for themselves do it, including myself. Clearly it can be hell to get it to work, but it feels great in the hand, lives very long, it's beautiful on the grain and needs maintenance once a year or two. – Dr.U Jun 18 '17 at 20:16
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    Some of the people asking all over the internet about tung curing times and behavior, are people wanting to finish their weapons with it, which was my case as well, and the info available is extremely scarce. That's why I wrote what I wrote, however too much in a rush, and made it sound like advice for general use in every application, which it definitely isn't. – Dr.U Jun 18 '17 at 20:21
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Lack of tackiness was my diagnostic determinant on my first project using tung oil (presumably the real stuff - a quart-sized container from Rockler that cost $25, I think - so it was at least expensive enough to be the real thing). I was finishing a microwave cart for my parents' kitchen after applying two coats of Minwax oil-based wood stain. Following the instructions on the container, I started with a 50/50 mix of tung oil/mineral spirits and then applied two thin coats full-strength (and maybe a third coat on just the top), wiping off the excess after 15 minutes. One day between coats might have been sufficient (according to the bottle) but I waited 2 days after some online research, and it didn't say to sand between coats but I may have done this as well. The cart turned out beautifully with a lovely, rich color, slight sheen and silky-smooth, non-tacky surface. It also had some extra curing time before we were able to transport it to my parents' house. This was over Christmas/New Year's of 2010 and to my knowledge it's never needed re-coating - although the microwave just sits on top so it doesn't get a lot of heavy use apart from drawers being opened and closed. I've been hooked ever since and will never go back to polyurethane if I can help it.

  • 1
    I'm a big fan of BLO for all the same reasons you outline, I'm sitting beside the first thing I did a full oil finish on and it looks just as good now as it did when it was completed ~5 years back, even on heavy-wear edges and corners. But, that hasn't at all convinced me I don't need poly. Poly is arguably the best hard finish available — inexpensive, makes the wood look great (better than shellac alone) and key, imparts good waterproofing. Plus it's just as easy to apply to a high standard as oil, with a wide range of surface finish possible as a bonus. So IMO don't discount it completely. – Graphus Oct 26 '17 at 5:07
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key to work with pure tung oil is mix it with other oils. for example you can mix it with orange oil (1/10 ratio). it will smell better, soak faster (depends on wood) and dry much faster (3days max.) from my experience..

  • 1
    Hi, welcome to SE. FYI, thinning or diluting products doesn't actually make them dry more quickly, it appears to but the effect is due to a smaller amount of oil being deposited on the surface and a thinner coat always 'dries' faster. – Graphus Jan 12 at 19:53
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I would certainly not presume to guess the reasons some have such difficulty with tung oil, but...

I got a fine wood carving knife about a week ago, and there was an aspect of the handle shape that was not right for my hand. I carved it to a better shape, sanded it, and then reached for an oil varnish finish I had used for years. Unfortunately, it had hardened in its container, and it was a snowy New Hampshire day.

In my shop, I found an unopened bottle of "Woodriver 100% Unprocessed Tung Oil" (a Woodcraft brand) that I had bought a while back, but had never tried.

My results could not have been better: Easy to apply, started to polymerize in less than an hour, recoats well after two hours, and the knife is ready to use in 24, after the last coat. I coat, sand with 600 grit paper, wipe off and it builds to a wonderful satin glow.

Beyond that, I appreciate the lack of toxicity.

Best to all,

Lothar

  • 1
    Unfortunately, this does not actually answer the question because any Answer will have to address that what is sold as "tung" oil varies widely, and trhus so does the application and results. Some appreciation for a data point, but the downvotes are probably a result of this answer being really just a single thin anecdote, rather than a general answer for others into the future. – jdv Feb 28 at 16:59

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