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Taking into account that different "Tung Oil" products take from a few hours to eternity to cure. Some say it never cures… Given the fact that curing is not drying… Being aware that some "Tung Oil" products don't even have Tung Oil in them…

I'm lost.

What practical indicators can I rely on to determine when my surface is ready for the next coat? Should I await it to dry or cure? Are there any straightforward tests, such as pushing the wood with a nail and observing if excess oil seeps out, that I can employ to gauge its readiness?

I'm asking because with my "Pure Tung Oil" even after following the instructions on the can, after 24 (in fact, even after 48+ hours) it is still oily and I am kind of unsure if I should really wait longer (or maybe help it dry with a fan) between the coats, or I am good to go.

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  • Hi, welcome to Woodworking! "even after following the instructions on the can" I'm not sure that's possible. Can you give the brand, or quote the application instructions? Cos the surface shouldn't be oily immediately after you're done, much less a day+ later!
    – Graphus
    Commented Oct 3, 2023 at 19:18
  • I presume you've read external sources on application of pure tung oil? Unfortunately there's a lot of misinformation and outright bad advice when it comes to finishing. This is for nearly any material but especially when it comes to the oils (where for example thinning the first coat is seemingly mentioned by >90% of people, without any verifiable data that it's beneficial). Anyway, if you didn't come across this on Pop Woodworking it's absolutely worth reading as possibly the best brief big-picture summary.
    – Graphus
    Commented Oct 3, 2023 at 19:54
  • @Graphus, I am using this product: bormawachs.com/dettaglio_new.php?idprod=3990. It says "Pure Oil". The instructions are on the page, and I follow them. Indeed, it said to dilute the first coats in 1:1 ratio, and I did so with a white spirit (I got it from my wife, she used it for her paintings and it was ok, so I am pretty much confident in it too). I wipe on some oil on the surface, wait about 10 minutes and wipe off the excess. Then I periodically, ~ 7 times per day, check it and wipe off with a paper towel. The wood is cheap, tho. A poplar ply. Appreciate the link, Ill check it!
    – madhead
    Commented Oct 3, 2023 at 23:30
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    "I guess, even 3 days is ok." Yes. The delay between coats is one of numerous reasons I'm not a fan of tung oil & have been actively trying to dissuade people from buying it since ~2013. "So, I still have the same question: practical indicators." Take one step back. I would have hoped that numerous sources would have emphasised what I said in my first Comment, that the surface shouldn't have been oily even immediately after application. As one site puts it, wipe like you mean it :-) The surface should feel cool to the touch and slick... [contd]
    – Graphus
    Commented Oct 4, 2023 at 6:04
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    ...but absolutely there should be zero detectable oil transfer to the skin; that simply indicates that not enough wiping has been done, because that is excess. I don't know about the legality of the copy of Flexner's finishing book Understanding Wood Finishing on Archive.org so I won't link to it in an Answer, but I highly recommend reading everything he has to say about tung oil in the 2005 edition.
    – Graphus
    Commented Oct 4, 2023 at 6:06

1 Answer 1

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I've used mainly BLO as a wood-finishing oil but I've also compared various other slower-drying oils periodically, basically to see how they stacked up to BLO. And in all cases, there was no absolute indicator that the surface was 'ready' for the next coat — to be perfectly honest often the surface looks and feels no different to when the preceding coat was first applied!

What practical indicators can I rely on to determine when my surface is ready for the next coat?

So as per the above, and sorry, but there may not really be anything concrete.

Because no pure oil actually cures in the interval between coats, what we're waiting for is enough time for the oil already applied to be absorbed more fully, and for the stuff nearest the surface to have cured enough1. This difference to the just-finished surface can be subtle enough that it's really only noticeable when you start oiling.

But despite some variability the surface should absolutely not feel greasy. Slick perhaps (usually not after only one coat) but not oily, much less transfer any oil to the skin......

after 24 (in fact, even after 48+ hours) it is still oily

From this and what you subsequently said in the Comments it is clear that your application procedure wasn't fully correct in the final stage, the wiping off.

As I expected, the application guidelines Borma Wachs provide for their tung oil don't strongly emphasise how rigorously users should remove excess oil the way they should..... as unfortunately most (almost all?) guidelines don't!

But with ANY oil you must remove ALL excess2. This requires dedicated, hard rubbing, and depending on species possibly a return to the wood over the next 12 hours or so to wipe away any excess that has weeped back onto the surface.

1 Which is not to say cured, as this takes weeks to months depending on variables.

2 All natural oils, even the best driers, cure to at best a semi-solid. What this means practically in a finishing context is that if you leave any on the surface (as distinct from absorbed into the surface) you will have a thin layer of that semi-solid on the wood after curing has progressed far enough. This will feel "draggy" or "gummy", or be noticeably sticky, very much not what we're going for.

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  • Huh, no simple answer is still an answer! Thank you. Now, in my particular situation, can I just switch to more intense rubbing for the next coats? I mean, to wait for the current, third coat, to dry to a state you describe (also wiping it of more frequently and vigorously) and then just apply a few more coat (I aim for 5) but this time being extra cautious and zealous to remove all off the oil at the initial wipe off stage?
    – madhead
    Commented Oct 4, 2023 at 7:57
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    Have you been doing any in-between sanding, or rubbing down with fine steel wool as Borma Wachs recommend? If you haven't so far, then doing this now will help to remove partially cured excess oil from the surface, which for most applications is an absolute must — needing to abrade between coats of tung is another reason I'm not a fan :-) With BLO (and every other oil I've tested by the way) depending a little on species and surface prep you don't even need to sand after the first coat, much less between each and every coat as may be recommended for tung oil, q.v. p77 of the Flexner book.
    – Graphus
    Commented Oct 4, 2023 at 11:06
  • I do a rubbing, yes, but with 000 steel wool, it's slightly more coarse than the recommended 0000.
    – madhead
    Commented Oct 4, 2023 at 12:12

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