tung oil

I applied several coats of tung oil/mineral spirits to a plant stand. For the final coat it said to apply pure tung oil. Well I did that and I'm still waiting after 4 days for it to dry. Should I have done this and/or will it ever dry?
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It will not dry. Oil finishes are not meant to build up a film. You are supposed to apply the oil and let it penetrate the wood for maybe 10-15 minutes and then wipe off the excess.
Frank
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With all those oil-based varnishes out there, I'm sure you must realize that oil finishes do build, and do cure, but they need help. That's provided chemically, by the addition of siccatives, or temporally.
"Pure Tung Oil" will require a lot of the latter, or it will require solvent removal and firming up with a tung-based varnish or tung with siccatives.

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I don't think this is the case. Oil finishes, real oil finishes like tung and linseed oil, will cure, but never dry hard enough to "build" a finish on top of the wood.
Oil-based varnishes are different. The oil in a varnish is chemically modified (by heat) so that it no longer has the same structure as oil. The amount and type of oil will affect how hard the varnish becomes upon drying (short-oil vs. long-oil).
Oil/varnish blends (such as Danish oil, Minwax Antique Oil Finish, or just about anything that calls itself "Tung Oil" without saying it's _pure_ tung oil) are yet another finish, simply being a mixture of any oil and varnish. They are not meant to be built, but I suppose if the amount of oil were small, you might be able to.
This is more or less culled from "Understanding Wood Finishing" by Flexnor. An indespensible reference, in my view, although others have their favorites (google the wreck for wood finishing books).
I have been having this same problem as the original poster. I attributed it to "low-odor" mineral spirits, which probably gets its low odor from using longer chain, less volatile (ie, longer drying time) compounds. After about 3 days, I put the workpiece out in the sun for an hour and it wept like a baby. It's not too bad now, so I'm going to try to put a spit coat of varnish on it. Could be a big mistake -- we'll see.
Greg
George wrote:

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Must have missed this article, I guess.
http://www.popularwoodworking.com/features/finish3.html "The Issue of Metallic Driers ff "
As stated, the _oil_ cures with help. If the wood is oiled to refusal, there _will_ be a "surface finish" of oil, it having nowhere to go.
Resins are added to improve surface hardness, at which point they become "varnish" regardless of the amount of solids. http://www.taunton.com/finewoodworking/pages/w00063.asp
If the solids are things like metallic salts (pigment), you get paint.
Infomercial at http://www.sutherlandwelles.com/tungoil.htm is pretty good on the peculiarities of tung. Folks who bought carvings in SEA during the distant festivities there can usually see tung surface finishes on their souvenir carvings.

This is more or less culled from "Understanding Wood Finishing" by Flexnor. An indespensible reference, in my view, although others have their favorites (google the wreck for wood finishing books).

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Well, my disagreement was not with the drying time, but the building of the finish. You simply can't build (where "build" is defined as to develop a useful film of finish exterior to the wood) a pure tung oil finish. OK, as Mike G notes, maybe you can get _something_, but it's pointless.
Your apparent statement that oil-based varnishes can be built therefore all oil finishes can be built neglects the different chemistry of the varnish (which, admittedly, I seem to have butchered).
As for the length of cure. Well, a week of waiting for the tung oil to cure on my atlas stand demonstrates the need for dryers quite well, eh?
Greg
George wrote:

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Well, personal definitions are certainly important, but qualifications such as "meaningful" can make communication difficult. Also difficult if you don't read the message for understanding, but for rebuttal. I recommended removal of the surface film (yep, can't remove the wood) and recoating with oil treated with either driers or driers/varnish, as preferred.
I'm not sure what makes us think we can slap on three applications in three days of an oil that says allow several days for the surface to cure. What we end up with is a curing film trying to be dissolved by the uncured stuff inside. If it takes days in open air, how much longer must it take in an oxygen-poor environment in the pores of the wood?
Oil is what makes the film in paint, in varnish, and on its own. Various ingredients, as I indicated, can make the film harder, color it, or otherwise modify its curing properties. Take a peek at the cap of your linseed, unless you're one of those fastidious types who wipes off the excess, and there'll be a tough, flexible amber-colored film on top of the impenetrable metal or plastic. It's wonderful stuff.
As you walk the hallowed halls of Dartmouth, remember that film - it's linoleum.

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The usual horse pucky.
Varnish by today's accepted definition is oil, carrier/thinner and RESINS that cross link and give a surface build.
Oil applied in sufficient quantity to build will, as the gentleman with the oil on the plywood found out, remain sticky for quite some time and will, as all pure oil finish do, provide little relative protection to the project.
For those reasons, while it is possible given enough oil applied to saturate the cells of the wood with enough cured to stop further absorption have it sit on the surface and cure to some extent, it is not only folly to attempt it but a monumental waste of time and materials when an actual varnish is available and designed to be a surface finish.
--
Mike G.
Heirloom Woods
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Did you wipe?
Brian.

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Did you wipe off all the excess from the surface of the wood after EVERY coat has set for the amount of time most likely listed on the can?
Leaving a thick coat sitting on the surface of the wood is the usual reason similar posts show up here.
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Mike G.
Heirloom Woods
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Pure tung oil is a hardening oil, and it *will* harden to a matte surface, although it can take a very long time. If your drying environment is reasonably warm (e.g., not in the basement), it may take anywhere from 2 days to maybe a week. In my basement, which is cool, tung stays liquid for at least 2 weeks when exposed to air.

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I have run into the same problem with tung and danish oil. As the previous posts imply, it is very important to wipe after 15-30 minutes. I have had wet residue stay wet for days. Try setting the project in direct sunlight, behind a south window or patio door, for a day or so. That usually works.

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Is this plant stand a piece furniture or something that is going to get wet from watering the plants? If it is a piece of furniture and not something you are going to slop water all over, I would remove the pure tung oil with mineral spirts and let it dry. I would them apply several THIN coats (5) of Tung Oil Varnish. This is a tung oil/varnish mixture with a dryer. Minwax makes it and is comes in a yellow can. You can pick it up most anywhere including Home Depot.
Make sure you wipe ALL the excess Tung Oil off after applying it. Sand lightly between coats with 600 grit sand paper. The tung oil varnish will dry fairly quickly depending on the humidity.
James
Makers of Small Table Making Software http://www.knightlite.com/creative

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