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Pure Tung Oil refuses to dry in 10 days - what to do?


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I made myself a nice table - sold beech table top, sanded to remove the old finish and applied tung oil instead.

Used a microfiber cloth to rub it into the wood and evenly distribute.

Few coats were applied same evening - it was a continuous process, because pieces of wood in the tabletop had different grain direction, so some were absorbing the oil pretty fast, while others did it slower.

Next morning I rubbed the excess oil with a paper cloth and left it to dry for a week.

10 days passed - it is still not fully dry. It looks pretty dry, but if you touch it - you feel that the surface is oily.

This is how it looks right now:

post-5430-0-76296000-1459115668_thumb.jpg

 

The oil I have is a local brand, not something well known. Bought in a fancy boutique though, which sells only high quality stuff :)

The can says that this is a pure oil and it dries "extremely slow" if not diluted with turpentine or some other oil:

post-5430-0-47578700-1459115771_thumb.jpg

 

It is too late to dilute :) Will read the instructions next time!

The same oil works fine on a model scale, but it feels different with small parts of a full size table top.

 

What should I do?

* Just wait more and it will finally dry? Should I wipe it with a paper cloth or sand it lightly, or it is better to let it untouched for a while?

* Apply some wipe-on poly on top of it? I am afraid that this will cause a mix of poly with half-dry oil, which might behave unpredictably.

* Apply another coat of oil? But if the current surface can't polymerize, new coat will not dry either.

 

Would appreciate any advices!

 

 

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Did you use a 50% solution as a first coat?  The most common method that I am familiar with is the seal the wood with 1:1 Tung oil: Mineral Spirit and when this is dry, wipe on light layers of straight Tung oil and let them dry between coats.  Ambient temp would affect the time interval.

The primer coat can also be 50% shellac -  the actual concentration would depend on your shellac source.  Orange shellac is (I think) 20 lb cut, but comes already in solution  - that means 20 lb to a gallon of alcohol - my rough  round up conversion is 20% solution.

I use Super Blonde flakes.  The refining removes impurities which affects the solubility - the max concentration I can get of this is 10% and therefore the primer coat is a 5% solution.  There are very low cost electronic balances now - so it is easy to weigh 5 g and add this to 100 ml 2-propanol (100%) - too much water in the rubbing alcohol concentrations (50/70/91 %) .  

 

You could start try removing some of the Tung oil with straight Mineral Spirits or turpentine and start over, but waiting a few weeks for the O2 to penetrate your too thick layer  and work its polymerizing magic is easier.  

 

I am thinking that pure Tung oil is not an ideal finish for a working surface.  A carving, a ship model, a wall surface - are great, but a surface subject to wear is likely not going to react like you would like. 

 

Here is a quote from Garrett Wade about Sutherland Welles pre-polymerized Tung oil products -  unfortunately this source is US only

 

"Tung oil is recognized as the finest oil finish available. However, most so-called Tung oil finishes on the market have been adulterated with varnishes, lower cost soy oils, and/or urethane additives. This makes the finish somewhat cheaper and easier to use, but sacrifices the special qualities of Tung oil. Pure Tung oil provides a tough, hard surface that is absolutely waterproof, and impervious to dust, alcohol, acetone, and fruit and vegetable acids. It does not darken with age as linseed oil does.

Sutherland Welles uses polymerization from a cooking process to give its Tung Oil a faster drying time and a harder, higher gloss surface. Increasing the percentage of polymerized oil in the formulation of the finish restricts penetration but increases luster, durability and hardness."

 

The highest polymerized product - 50% -  is suggested for table surfaces -  The cost is significantly greater than pure Tung oil so reading between the lines -  it would not be sold unless its characteristics were not needed.

Edited by Jaager
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Jaager, thanks for the detailed explanation!

 

Did you use a 50% solution as a first coat?  

No, I used a pure oil.

 

Understood the idea, will wait more, if it will fail to dry - will follow your instructions on removal and re-application.

Oil might not be not ideal for the working surface, but I really do not want to have a glossy look of the typical varnishes, that create a transparent layer on top of the wood. Probably will end up sanding and re-finishing the table top once or twice a year, it is fine.

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I have a bottle of the "Danish Oil", this one: http://www.wood-finishes-direct.com/product/rustins-danish-oil

It contains "purified Tung Oil, vegetable oils and resins."

 

Does it make sense to apply it on top of tung oil, as a second coat? Danish oil should dry much faster.

Or it is better to avoid mixing different oils together?

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Hey Mike,

 

The proper way to apply pure Tung Oil is 50/50 cut with Mineral Spirits for your first coat.  Let that dry 24 hours which lays your base for uniform penetration. Then you apply full strength - let it sit for 15 minutes or so before buffing out. Continue to monitor for seepage and always allow 24 hours between coats.

 

It sounds like you should just let the piece gas out - applying Danish Oil on top could compound your problem. Hope this helps

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A little heat will increase the drying rate.  A few (incandescent) light bulbs will do.  Lean your table top against the wall to form a tent and put a lamp or two inside.

 

By the way, apply a coat to the bottom of the table top to limit moisture getting in or out to fast that could cause the plank to warp.  

 

I'll throw in the classic concoction I use for work bench tops and furniture that will see some use.  1:1:1 mix of linseed oil, mineral spirits and varnish.   I suspect you can substitute tung oil for the linseed oil.  It penetrates deep, is somewhat hard, but the surface is not smooth or glossy.   It does create a slight amber tint though.  Since oil-based varnishes are getting hard to find, I tried a water based version for my last batch.  It worked well and doesn't seem to separate in the can.

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"Few coats were applied same evening"

If 1 coat takes a few days to dry, how much time take 5  thick layers? 1 month or 2

 

50-50 mix  dry  about half the the time of  a 100% tung oil because there is about 50% less of oil

 

50-50 mix is applied so that the oil penetrates deeper but how much deeper? Also tung oil is not the champion to penetrate rapidly in the wood. To mix with odorless turpentine is helpfull

 

The usual way to apply a coat; wipe 1 coat wait 15 minutes and wipe the excess, because there is always excess because of the poor penetration factor of tung oil

 

Finally do not use Danish oil, your wife will not like the smell, and if you absolutely want to mix with turpentine use odorless turpentine  because again your wife will not like it

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Gaetan, thanks for advices. I understand now how much of an idiot I am.. Lesson learned! 

I really had very little understanding of the mechanics of oil.

 

Already tried regular turpentine as a dilution liquid on some scrap wood - even I can't stand that smell, threw away the entire bottle next morning!

Will test white spirit (mineral spirit) solution on a scrap wood today. And for the table top - will just leave it as is.

 

Question: would it be beneficial to sand it with very fine paper from time to time, to smoothen the grain? Or it will cause more harm by removing the top layer that is drying?

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Mike,

It's nothing that can't be remedied.

I would wipe the surface over with mineral spirits every 12 hours for a couple of days. As it evaporates it will dry out some of the oil. When the whole thing is dry, then add very light coats of Tung oil until you have the surface you require. 

 

Dan.

Edited by overdale
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Id use a type of wool - super fine steel wool - or even brass wool - which I hear doesn't shred as much in between your two coats.  Your first coat of 50/50 will absorb pretty well.  Not sure if you decided to sand off the earlier coats though - so not sure what the effect may be.  

 

I'd leave your second 100 percent strength Tung Oil as is.  As Gaetan says - do not let the full oil sit on the piece more than 15 minutes before removing and watch for seepage.  

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Hi Mike

 

I coated a new timber floor (2nd hand Australian hardwood) with pure Tung Oil, so no thinners, no resins etc - sounds the same product that you have used.

 

We did one coat, it was spread fairly thickly, really wet, then about an hour later the excess was wiped off. No walking for 24 hours, & the result was good. I have also coated a plywood floor the same way, that time using multiple coats which did build up but at times didn't seem to be setting.

 

They both cured, but it is different to other finishes & didn't feel dry in the way that a polyurethane finish feels dry.

 

It does sound like yours isn't curing - my understanding is that it cures in the same way that boiled linseed oil cures, a chemical reaction, so you must not bundle up rags that are soaked in the stuff, it releases heat in the reaction & can ignite. So I'd be careful about diluting without checking my recollection that it cures rather than dries, & also that it will still cure if is diluted...

 

On the question of a satin finish, with furniture I often do my build up coats & then as a final coat let it half dry & then wipe it off with a rag to give a greasy look, it replicates the finish that wax polish that hasn't been buffed has.

 

Hopefully this helps, best wishes.

 

Mark

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  • 3 years later...

Dan and ‘ye all’ please answer this:

I’m trying to use none toxic products and came across Tung Oil which I used neat on my own dining table. It turned out well and my daughter asked me to do her oak table which is 3x size of mine. In this instance I did sand off (very thoroughly) the previous wax finish. I gave it several coats wiping off the excess afterwards and leaving for 24 hrs. The table had been placed outside on a covered patio for the sandiing  etc and left outside for the whole process. I noticed white spots appearing and it seems to have got progressively worse, despite resanding those areas. I’ve had such conflicting advice so even contacted the manufacturer who advise stripping it all down again with ahydrocarbon based ( benzine in South Africa). This seems quite drastic and defeats my whole objective of a toxic free procedure. I’m sure is more to do with moisture than any athivnag else. Your thoughts greatly appreciated.

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On 4/6/2019 at 12:09 PM, Kathryn said:

Dan and ‘ye all’ please answer this:

Kathryn, pretty clearly no one has an idea as to what is happening here. Usually white patches and blushing is moisture being trapped under the finish, but that is seen with film finishes, not oil.

 

The second major possibility is silicone, as people will use paste waxes or dusting products that include silicone and once silicone is on a piece of wood you'll never get it off no matter what you do. But again, that usually impacts film finishes, causing what are called fish eyes. I don't really know what silicone would do reacting with tung oil, so that could be your problem.

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My understanding is that Tung oil polymerises in the presence of oxygen. So with time it will turn into a plastic like polymer. The 50% dilution is to allow it to penetrate deeper, thus giving better protection. 

I have a container of pure Tung oil that I have been using for years (its almost empty now), squeezing the metal as the oil gets used up so that there is as little air in contact with the oil as possible. If I do not open the bottle for 4-5 weeks, it is then very difficult  as the oil in the cap polymerises and solidifies. Opening the bottle earlier is fine so really it takes many weeks for a full cure.

Tung oil finish takes a very long time as many thin coats needs to be applied, waiting a few days in between for some degree of cure to happen. I remember reading that in ancient China it could take a year for a Tung oil finished table to be ready.

There is also polymerised Tung oil I think that cures much faster, the equivalent of boiled linseed oil.

 

My 2 cents!

Edited by vaddoc
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  • 8 months later...
On 3/28/2016 at 5:08 PM, lehmann said:

A little heat will increase the drying rate.  A few (incandescent) light bulbs will do.  Lean your table top against the wall to form a tent and put a lamp or two inside.

Supposedly, tung oil won't spontaneously combust like linseed oil can (and will under the right conditions.) I've made it a practice to never leave any oil-based products unattended until they have dried and never to subject them to heat in any enclosed space without a lot of forced ventilation.. I've no concerns about a coat of oil, varnish, or paint on a surface exposed to well-circulated air, but I'd be very leery of enclosing any oil-based coating and adding any sort of heat source into the mix. There's just no telling whether, under the right conditions, gasses or the coating itself might reach "critical mass" in an enclosed, stuffy space and ignite. Particularly oily rags and also paint brushes and steel and bronze wool must be stored underwater in a bucket or hung outdoors in the air to dry completely before disposal. Similarly, mixtures of epoxy resin and hardeners are susceptible to exothermic reactions and can "cook off" unexpectedly when the heat generated by the curing process accelerates the curing, creating a "chain reaction" in which the mixed epoxy rapidly gets hotter and hotter until it ignites whatever flammables are nearby. Just sayin'. (Don't ask me how I know this stuff! :D )

Edited by Bob Cleek
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1 hour ago, mtaylor said:

Bob,

So a hair dryer (for example) fixed such to blow across the wood in garage with a window or two open shouldn't be done?   I recall my dad doing this for some projects when I was kid.  

It's one of those "use your best judgment" sorts of things. A hair dryer should be fine from a safety standpoint. You're standing right there doing it. Hair dryers don't get that hot to begin with. If things start to smoke, or catch fire, you should be able to put it out without much problem. (Every shop should have fire extinguisher(s.)) On the other hand, building a somewhat air-tight tent over a piece of work that is out-gassing volatile gasses and putting a couple of light bulbs burning in it to "heat things up," and then going to bed, isn't something I'd recommend. It may be no problem at all, or ... . Any product that says, "Use only in a well-ventilated area.", is probably flammable. Treat it accordingly. It's just common sense.

 

As your dad probably discovered, a hair dryer will cause water to evaporate and whatever is wet, like hair, will dry when it's blown with one, but as for getting paint or varnish to cure quickly, blowing air over the surface is probably more likely to ruin the finish by stirring up dust than it is to do anything productive. Additionally, accelerating the drying of the top surface of a coating, while leaving the lower part unevenly cured beneath it is likely to ruin the finish. It's one way get a "crinkle finish" as the top dries hard and then the lower part later dries and shrinks, scrunching up the harder top layer.

 

Edited by Bob Cleek
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