Monthly Book Giveaway - January 2023

Most Tung oil directions get this wrong

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I don't get it.  Pure Tung oil is a fantastic finish, but nearly every article I read and even the product directions make what I think is a mistake.  That mistake leads to failed finishes and disgruntled woodworkers.

Bad advice #1: Flood the Tung oil on the wood

The recommendation I see in articles AND the product directions are to thoroughly flood the wood with thinned tung oil until it will drink no more.  Then wait 3-5 days for it to cure before adding more coats.

Tung oil is a drying oil and cures due to polymerization with oxygen.  Flooding the workpiece with Tung oil only insures that you fill the fibers with so much oil that will never see the light of day and will take years to cure internally.  Tung oil cures at the boundary of oil and air. So the surface that contacts the air, will skim over leaving the oil trapped beneath starved for oxygen.  Contrary to popular opinion, the wood is not nourished by oil, nor does it have a thirst that needs to be quenched.  Trapping oil super deep in the wood is nothing but heartache waiting to emerge.

My suggestion is put on a decent coat, no flooding, then give it time to cure WELL.   Give it at least 7 days. When the rag you put it on with is hard and crusty, it is cured.   When the first coat is cured, the wood will not soak up as much oil on the second coat.   If you just keep putting more oil on without giving it time to cure, the wood will appear to keep drinking it in, because it is. It is drinking it in and adding it to the reservoir of uncured Tung oil lying beneath.  Each successive coat should be light.

Bad advice #2: Keep it out of the sunlight

Many articles suggest keeping Tung oil out of the sun because it causes it to cure more rapidly, then bemoan that Tung oil takes so long to cure.   The truth is that UV light causes Tung oil to cure ~30x more rapidly.   Yes if you slather the wood with Tung oil and you put it out in the sun, you will get a wrinkled tacky mess.  However, if you put on a really light coat and wipe it off as completely as possible, then put it in the sun, you will have a nice finish that will be ready for another coat the next day. 

Source article with more details: What most articles get wrong about Tung oil
 

26 Comments

Interesting I so. Thanks! It’s funny how many different application ‘patterns’ I’ve been told about for Tung Oil. 

Ryan/// ~sigh~ I blew up another bowl. Moke told me "I made the inside bigger than the outside".

never used pure tung oil before. ive used the maloof formula for many years. 1/3 tung, blo, and poly. love the finish and dries for a re coat in a day. 

working with my hands is a joy,it gives me a sense of fulfillment,somthing so many seek and so few find.-SAM MALOOF.

You might want to edit the post and change that to "hardening," since the tung oil and other hardening oils harden, rather than dry  ("[T]ung oil is a drying oil. . . ."

Regarding your directions, keep in mind, some tung oil is pre-polymerized, so you do not have to wait any longer than you would if you were applying polyurethane, before you add the next coat. 

Sadly, the place I used to buy gallons from is no longer in business (Winthrop, Washington). They sold wonderful, pure tung oil they treated at their plant. When others were charging absurd prices for a quart, they sold it by the gallon for about $30.00. You could also buy the additives to bump up the hardening process.

So, what do people mean by "nourish the wood"?  I've seen articles mock that, but no one explain what it is.

I know that I am one of those people who has no qualms about adding hardening products and non-hardening oils to wood, "as long as it will drink it up."  Decades back, I used to make burl and stump tables.  I'd flood the slabs and stumps with thinned poly.  I had a 5" thick piece that was wet on the bottom from the  I know of one which sat in front of a well used fire place and never developed cracks from further moisture loss.

At the same time I made burl tables [and clocks], I did a "little resin work (I bought the resin in five gallon buckets (50/50 or 1:1 mix). If I didn't seal wood before flooding it with resin, I'd get air bubbles. Lots of air bubbles at the bottom of the initial layer.  That explains why my hardening applications did not take months or years to harden. There was enough oxygen in the wood to react with the various hardening products (thinned poly (so drying and hardening), Plastic Oil (Varithane product, and so on).

A certain noted expert on finishes claimed people like me were wrong and harding of wood was just a Varithane promotion. Now days, it's accepted that oxygen activated or heat activated resins sold to harden rotted or punk wood and other things (e.g., Cactus Juice, Daley's Sea Fin, etc.) actually do harden wood, via penetration. They fill the cells, then harden.

On a side note, when I use Cactus Juice and have to remove as much as the air as I can, to increase penetration. If I don't put wood in my vacuum chamber, penetration is greatly reduced (some pieces nearly double in weight, after having a vacuum put on them, then filling them with Cactus Juice or even a product like Daley's Sea Fin.

ANYWAY, the reason I often go all out treating wood is simple, wood shrinks and cracks as it dries. Adding oil that deeply penetrates will reduce moisture gain and loss, reducing cracking and splitting. Too, it will, if kept wet long enough, or if a non-hardening oil is used, swell the wood and can even hide small cracks and splits.

Key to getting the same effect you would with a non-hardening oil is, keeping the surface wet as long as possible to hold off surface reaction (hardening).  

All that said, it drives me nuts when people talk about flooding a surface and, immediately, wiping it off. What a waste of oil.  Like you, I'd wipe on what I need to, to get coverage [without orange peel] for tung oil or linseed oil. For mineral oil on a cutting board, or other oil on a fence or other non-food item, I'd let it sit and soak in.  


You might want to edit the post and change that to "hardening," since the tung oil and other hardening oils harden, rather than dry  ("[T]ung oil is a drying oil. . . ."

This might be a regional thing.  Nearly all the references I see to Tung, Linseed or Walnut oils use the term "drying oils "  as opposed to a search for "hardening oils" returns mainly references to oils used in hardening metals during the quench.

...keep in mind, some tung oil is pre-polymerized, so you do not have to wait any longer than you would if you were applying polyurethane, before you add the next coat.

I am only talking about pure Tung oil here.  not Tung oil finishes or other modified variants.


never used pure tung oil before. ive used the maloof formula for many years. 1/3 tung, blo, and poly. love the finish and dries for a re coat in a day.

@pottz   I often wondered why Maloof chose a mixture of BLO and Tung.  On one hand, the same driers that are in the BLO will cause the Tung to cure faster.  The BLO will also add a bit of warmth that Tung lacks (tung imparts little color) .  But I also wonder if it has similar failure points.  BLO feeds mold and does not hold up well to sunlight or water.  I am not sure if the Tung overrides those weak points 100% or just cuts them in half.  And does the Tung prevent the BLO from darkening with age?  So many questions, so little time to experiment ;)
I have no answers to these conundrums, but I feel like if it had failure points Maloof wouldn’t have used it for so long and with such success. Of course I could be wrong…

Ryan/// ~sigh~ I blew up another bowl. Moke told me "I made the inside bigger than the outside".

Thanks for this, swirt! I tend to do thin coats plus use the NM sun (UV index 14!) to help things along, but on punky wood, I’ll soak the piece and leave it sit for weeks or more to firm it up, though I usually do that with BLO with heavy metal driers so it cures quicker.
I understand "polymerized tung oil" has chemical driers in it... this is what I use in my work. The alternative...conventional tung oil takes forever to dry. Also, after flooding and giving time for the wood to absorb the oil (a few minutes), the remaining tung oil needs to be wiped off. This leaves no surface film (what we are striving for)  and allows the tung oil absorbed in the wood to harden. 

Norman Pirollo

Swirt, pre-polymerized tung oil is pure tung oil, just like boiled linseed oil is pure flax seed oil.  As I mentioned, the company I used to buy from also sold the hardeners to add to the Tung oil they had pre-polymerized via processes, just as linseed/flax seed oil is treated to speed hardening, so it will take place in hours, rather than days. 

As we know, there are products, like Fromby's and Watco [so called Danish Oil], that have thinners and resins added, making them just thinned polyurethanes.  In other words, though you, initially described it as a drying product, your description went on, in the third paragraph, to properly describe how Tung oil hardens.

Finish experts throughout the U.S. describe the hardening process for both linseed oil and Tung oil as taking place by way of reaction with oxygen, rather than by way of evaporation of  added solvents, or drying. 
RyanGi and Swirt, it may be Maloof choose the mix for the fact the BLO darkens wood.  Many of us who have decades of experience working wood and finishes develop preferences that could even be called biases.

The idea that Tung oil might lessen mold problems is an interesting one with potential, so shouldn't be dismissed.  That said, I cannot fathom using a hardening oil without resins (polyurethane) in an environment prone to mold. It's not at all durable in, for example, exterior applications. BUT, mindful of the long oil thing, it might be a penetrating application would do well in shifting with the wood. Then, with the addition of polyurethane, mold is not going to find it a tempting meal.

As to adding BLO or Tung oil to poly, that moves it more into being called a long oil finish, which is just a way of saying a finish has more oil than a short oil finish. 

More oil makes a finish less durable, but more flexible, which is the reason they use it for nautical finishes (it tolerates shifts in the wood, caused by moisture gain and loss, more than short oil finishes). Short oil finishes are preferred for floors, for their durability.
The comment about him potentially using BLO to darken the wood, and about forming a bias certainly rings true. I’ve found when I’m using clear finishes and want a little more depth to the wood I use BLO first. I’m sure someone somewhere told me it would help the aesthetic, but now it’s just something I do when that’s the look I want. 

Ryan/// ~sigh~ I blew up another bowl. Moke told me "I made the inside bigger than the outside".

In the south, anything kept in the dark is prone to mold.  BLO has been a stock finish of choice for firearms for many years.  When I open my gun safe I can just by sight tell you which ones have BLO finishes.  They are often covered in white fuzz.  The ones I finished with Tung are not.

Related to out doors.. I have several pieces of furniture that are a couple years old and treated with Tung oil that are holding up well considering they have endured two significant hurricanes.  Poly would already be suffering from the UV.  Will upload some photos tomorrow.
Swirt, pre-polymerized tung oil is pure tung oil, just like boiled linseed oil is pure flax seed oil. 

That's sort of right but not quite.  BLO is not pure flax seed oil.  It is flax seed oil and metallic driers added. Pure flax seed oil is edible, BLO... Not so much.
I bought some pure Tung oil from Lee Valley. 

I made the mistake of putting on a thick coat and it took what seemed forever to dry. Your right about applying thin coats. 

I does leave a beautiful finish when it’s dry. 
It’s not for projects that need a fast drying finish. It is great for food related projects. 

Pottz. What type of poly does you mixture require and how long does it take to dry?

James McIntyre

Swirt, it is you are mistaken, and not, regarding converting flax seed oil to boiled linseed oil [BLO]. 

The pre-polymerization process was first done and is yet done by blowing air through vats of flax seed oil. The oxygen in the air, about 21%, reacts with the flax seed to make BLO.  It was heated too, but the air blown through it made it look like the oil was boiling, thus the name BLO.

The process of using air to pre-polymerize oil, like many things, depends on art, in addition to routines and ratios.  Too much air and a batch can be lost.  If the oil was allowed to boil, the batch would have been ruined by too much heat.

It was after it was discovered flax seed could be pre-polymerized, to speed up hardening, by blowing air through it, it was learned adding certain heavy metals to it would, also, speed the process.   Again, too much can destroy the product to which it is added.

Not all BLO has heavy metals, though it has become more common.  Again, the boiled part of the name came from blowing air through the oil. It did not come from adding heavy metals. 

The end result, whether by blowing oxygen through the flax seed oil, by adding heavy metals to the oil, or by doing both would be the same - hardened flax seed oil, in time.

As to the pre-polymerized Tung oil I bought, it is presumptuous to insist it had heavy metals when you were told it did not. Such presupposes I didn't know about the product I was using, and the processor was less knowledgeable on the matter than you, or lying.

As I said before, I bought pure Tung oil the company pre-polymerized.  Just as is done with BLO using other than chemical additives. It hardened quicker than pure, raw Tung oil, and quicker yet, once I applied the heavy metal additives to the product.
If you want to know all about linseed oil refining, use in oil paints, etc., Tad Spurgeon’s book can’t be beat. Here’s a link directly to the book. It also covers tung oil and walnut oil, though mostly dismisses them, because Tad’s methods will give a linseed oil which yellows very little (which is the primary reason for artists look at things other than linseed oil).

If you just want to know about refining linseed oil (he gives six different methods, none of which involve Japan driers), there’s a 16 page excerpt which is more digestible.
@dave polaschek there is a very informative video here  that essentially covers Tad Spurgeons' method of refining linseed oil and pre-polymerizing it with sunlight.

The quality of the video is a little rough, but the info is fantastic. 


Kelly I am not doubting your knowledge on this.  I think where we are getting off on the wrong foot is in switching back and forth between modern uses of the terms and much older uses of the terms.  And yes the terms should not change, but corporate marketing and products have forced them to. 

Example 1: the process you are describing for BLO covers less than 5% of what is being sold under that name now.  When people buy BLO today, most are getting the metallic driers variant which makes it not just pure linseed oil.

Example 2: polymerized or pre-polymerized Tung oil.  As near as I can tell, there are only two companies selling that (Sutherland Welles? and Waterlox?).  Neither of them refer to their product as 'pure Tung oil'.   The only products on the market labelled as 'pure Tung oil' are not pre-polymerized.
Photos of tung oil on outside stools

The one on the left was coated in 2020, the one on the right in 2021.
The orange tinting comes from the zinc which is added to Tung oil to make "Outdoor defense oil"   I believe these both had 2 initial coats of outdoor defense oil, then a few follow-up coats of pure Tung oil.  
Despite being outside in coastal florida all day long (not always in direct sun like the photo) and rode out the abrasive effects of 2 major hurricanes, the are doing remarkably well.   They were kind of a test, and so far I am pretty pleased with the results.
Photo of BLO vs Tung oil on firearm stocks kept in the same gun safe. Both cleaned and put away a little over 6 months ago.   The little white dots on the stock on the left are mold.