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Tung Oil Drying Time

Keef's picture

Tung Oil Drying Time (post #110994)

I've used quite a bit of 100% pure Tung Oil with fine results.  Usually, I hang up the rag I used and when its stiff (the rag) I call it "dry".  I do this with all the wipe ons.  Based on my experience, it usually it takes between 16- 36 hours to get a stiff TO rag to dry. 


I have noticed that when you wet sand a finish, the drying (stiff rag method) takes considerably longer.  I've found this true with Oil/ Varnish and with TO.  Does anyone know why this would be (a rag with oil dries 5X faster than a rag with oil+ saw dust slurry)?


Why I'm writing is that the my current TO project (8"X 12" box)  has been drying for 7 days and the rag is still not stiff (which means the finish is still not "dry").   I want to apply my shellac!


I know that many of the fine posters here will say TO takes weeks/ months to dry, but that has not been my experience (except with the wet sanded method).  My TO is fresh (or at least I just bought it from Rockler) but after 7 days, the cotton rag is still not dry.  How do some of you determine if a TO finish is dry enough to overcoat with shellac?

Rich14's picture

(post #110994, reply #1 of 10)

Keef, Your tung oil may be FRESH and 100% PURE, but has it been heat treated to hasten the polymerization process, once applied to wood? ( http://www.sutherlandwelles.com/products.htm ) Pure, unadulterated tung takes months to harden, if not years. I've known some test pieces that were soft 4 months after I applied the finish, and probably would have needed two to three times that to be called ready for even gentle handling. I can't fit that kind of drying schedule into my lifetime! Rich

HowardAcheson's picture

(post #110994, reply #2 of 10)

>> Does anyone know why this would be (a rag with oil dries 5X faster than a rag with oil+ saw dust slurry)?


Because the sawdust absorbs the tung oil and you have a much greater amount and thickness of tung oil. 


In fact, the non-drying of the slurry soaked rag is more representitive of the length of time that it takes tung oil to polymerize or dry in the wood.  It's a very slow process with tung oil.


Why are you using the tung oil?


Howie.........
Howie.........
Keef's picture

(post #110994, reply #3 of 10)

>>Why are you using the tung oil?<<


I started using it because it was easy and the results were always good.  I'm using it on this project to enhance the figured grain of the cherry I'm using.  Jewett's book made me do it (Tung Oil under the top coat).  I'm starting to question if I'm using it right.  For this finish, I mixed it 1 to 3 with mineral spirits, so it was not applied full strength.  Is T.O. a poor choice?


KB 

HowardAcheson's picture

(post #110994, reply #4 of 10)

IMO there are only two things that pure tung oil is usefull for.  One is to make a marine varnish and the second is to add some color to darker woods to "pop" the grain or figure.  It is somewhat less amber than linseed oil and, in general, I like to use BLO rather than tung oil.


I use both pure tung oil and BLO as coloring treatments, not finishes.  As a finish, they are both poor.  Neither offers much water or water vapor protection and neither provides any abrasion resistance.  Both require frequent re-application to maintain the slight gloss they impart to wood.


Howie.........
Howie.........
cadiddlehopper's picture

(post #110994, reply #5 of 10)

If your tung oil dried in 36 hours, it was not pure. There had to be a drier of some kind in it or it had some kind of treatment to speed polymerization. I presume you wet sanded with mineral spirits as the wetting agent. That probably made little difference but someone else will have to make that judgment. I suspect that your products are variable; different brands, maybe. I gave up the pure stuff myself.

Cadiddlehopper

Rich14's picture

(post #110994, reply #6 of 10)

Cadiddlehopper, Even polymerized tung oils are sold as "pure." That's to distinguish them from non-tung products that are still labeled "tung oil" or products with some tung oil, plus other oil(s) and varnishes. Rich

Keef's picture

(post #110994, reply #7 of 10)

Thanks for the feedback, its been very informative, including the link to Sutherlands that Rich sent .  Just to clarify- the rag that is dry after 36 hours. 


THe  TO- its Rockler brand- says  "pure tung oil..No harmful lead, petroleum distalates or chemical dryers are in this product..."  I might have give it up myself .


KB

cadiddlehopper's picture

(post #110994, reply #8 of 10)

Rich: I am certain that you are correct. Labeling of tung oil products is a bit deceptive to me. I had used a tung oil varnish for a couple of years thinking it was tung oil due to the labeling.

Cadiddlehopper

SteveSchoene's picture

(post #110994, reply #9 of 10)

But, they will also tout the fact that they are polymerized, which though it does make application trickier, it also does have benefits in durability. 

Test your finish on scrap, FIRST, or risk having to scrap your finish.

Rich14's picture

(post #110994, reply #10 of 10)

Yes.