Thoughts on Tung oil finishes & advanced methods

[Sadie-f]

Having completed at least rev-1 of my tung-finished guitar, I wanted to clarify some misunderstandings about pure tung oil. The pinned post in the finishes forum is great, I have one pint to better clarify:

These oils are usually not built up with enough coats to form a surface film, like that of varnish or lacquer, because the film is too soft

I think it's more accurate to say they're not built up to film-forming more because  that would require a completely stupid number of coats. My experience with tung has been it's quite a bit harder than traditional varnishes, to the point of being almost brittle, if you scrape a tung finished surface, it comes off like a powder. On the flip side, small scrapes are very easy to repair. Because it's so thin, just clean the damaged spot, wipe on a bit of tung and wipe it off later. such blemishes may be visible, imx they're hard to spot.

By comparison, if you scratch a varnished surface, sometimes you can buff it out, however, to get back to original, you pretty much need to lay down new to the entire part, or accept a visible brush - in.

My main experience with varnish finishes has been applying traditional spar varnish to spruce for masts etc in marine use. The best of these all have some tung oil, in addition to other resins (usually phenolic, sometimes alkyd). I've also sprayed / brushed iso-cyanate paints on boat hulls, All these finishes live outdoors and the marine paints are more or less interchangeable with what auto manufacturers use.

Many members here question the water-protection from oil finishes. My first experience with tung was a  dining table and chairs I refinished in pure tung and that finish was still in fine shape 20 years later, including children, projects done at the table, etc.

To get that protection, you  want to get out to at least a half dozen layers, for that table as well as the new Strat build, I went to 15 & 20 respectively. It's definitely more time consuming than laying down spray or brush varnishes, and you have to be want to see the still-visible grain. I suspect to get completely past that in most woods would run out to 100 layers, at which point it would probably look like a finish you could achieve with a couple of layers of spar varnish. 

 

[Sadie-f]

Here's an addendum. While I came into finishing a first guitar build with past experience of doing oil and varnish finish on many more total ft^2 of surface of furniture and boat spars, I learned a lot new with a guitar body build.

1. Polymerized tung can accelerate building layers by ~2-4x, with the downside that this adds mineral solvents, so I would not use it for anything I'd eat off of, or in early layers on a guitar. For a pedal board, however, I went polymerized for most of the layers

2. I used Lee Valley brand for polymerized, and went with their high lustre (other vendors have similar grades). They also have a polymerized sealer that they recommend to thin the high lustre oil for easier use. They're correct advising that the higher concentration version is not very forgiving. If you step away for an hour between wipe on and wipe off, high lustre will congeal to a sticky mess. Luckily, the one time I did this, it was still recoverable.

3. Partly by accident, I learned it's possible to use sunlight (UV) to set polymerized tung much faster. A fresh layer may be set in winter sunlight for 5 minutes and be at the perfect point to wipe down. Another 5-10 minutes in sun after wiping, perhaps with an intermediate wipe down to catch oil that comes up out of the wood grain, and I found I could add new layers in a 30-40 minute cycle.

4. This can also be applied to pure tung, however the much slower polymerization and greater difficulty building up/filling grain means that what beads up from the below surface needs to be removed quickly. So far, I've only worked pure tung in warm weather; cooler weather will probably be different. This will be an on-going experiment with my maple soloist. When I have the time, it's great to get more than a couple layers per day. Otoh if I can only do one in a day, no need to accelerate the cure time.

5. Pure tung can be layered at 24 hours, however I've had the best luck with alternating between 24 & 48 hour delays between application.

6. I prefer to thin a first layer of tung with ethanol. They're not perfectly miscible, however enough to be workable. Also I have pure ethanol and isopropanol on hand at work, and so it's more convenient.

 

[Lbpesq]

I’ve done several builds with Tung Oil.  I love it as it really shows off the wood.  Most of these have been on Black Korina bodies.  I use mineral spirits in a 50/50 mix for the first one or two coats, then switch to pure Tung.  I wipe it on, wait about 1/2 hour, and wipe it off.  Every third or fourth coat, I wipe some on and do a light “wet” sanding before wiping off.  I then usually wait 24 hours to do it again (dictated by my schedule).  I do around 15-20 coats.  Then it takes 2-3 months to fully cure.  At that point you can burnish it and really bring out the luster.  I recently obtained some polymerized Tung Oil.  I thought I would try finishing off the pure Tung Oil with a couple of coats of the polymerized stuff on my next build.

Bill, tgo

 

[Sadie-f]

I’ve done several builds with Tung Oil.  I love it as it really shows off the wood.  Most of these have been on Black Korina bodies.  I use mineral spirits in a 50/50 mix for the first one or two coats, then switch to pure Tung.  I wipe it on, wait about 1/2 hour, and wipe it off.  Every third or fourth coat, I wipe some on and do a light “wet” sanding before wiping off.  I then usually wait 24 hours to do it again (dictated by my schedule).  I do around 15-20 coats.  Then it takes 2-3 months to fully cure.  At that point you can burnish it and really bring out the luster.  I recently obtained some polymerized Tung Oil.  I thought I would try finishing off the pure Tung Oil with a couple of coats of the polymerized stuff on my next build.

Bill, tgo

Yep, same routine with wet sanding during the progression, starting at 220, up through 600-1000.

With polymerized, do what you can to minimize air exposure. If I'll be doing say 4-6 applications in a day, I'll draw off several ml into a disposable pipette. If I buy another container, I'll draw off 1/4 into a smaller container at work and blanket the original with argon or nitrogen.