Tung oil advice?: on stain, under topcoat (this was a PM to me)


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This was sent to me in PM, from another user, and its best discussed in the forum, so I posted it here (hiding his email address which he gave at the bottom).

Tung oil advice?: on stain, under topcoat
« Sent to: =CB= on: Today at 02:36:46 pm »

Hi, I'm an amateur guitar luthier and in my searches for finishing information, especially on tung oil finishes (which are severely under-documented), you seem to be the single greatest source on the subject. Thus, I come to you, seeking your word on my approach for a few specific situations. Initially I used the Finishing book by Jeff Jewitt for oil finishing information, but he leaves out a few key instances:

1. I intend to stain a body (mahogany) and the binding (bloodwood) around the headstock on a second guitar (both guitar necks - from tip to heel -will have a simple oil finish). I was going to use a liquid concentrate dye in alcohol solvent and apply it with a spray gun(quick side question: I want the grain to be as defined as possible as well as maintain even color, so should I wipe the stain after application or not?). Out of all the different alcohol solvents (denatured alcohol, ethanol, methanol, Behkol, NGR, etc) which one would be safe to use when applying the 1st coat of tung oil (which I was going to thin with mineral spirits). I would like to re-use the stain in some shading on the other guitar so I was thinking of using NGR reducer because its neutral effects on the spraying lacquer. Will NGR reducer be safe to use with a later application of mineral spirits? If not, what do you recommend?

2. In the book it also makes comment about a light coat of tung oil under a lacquer topcoat to eccentuate the grain which I was going to do on the bodies and headstock faces. The lacquer topcoat, that is. Of course, I would seal the wood with shellac or vinyl sealer before spraying the lacquer. What are your thoughts on this?

Provided that I decide to do so, I have some concerns. On the stained body, would a coat of oil be pointless? I have heard that dye stains build depth in the wood due to the fact that the stain absorbs into the wood and that they are transparent - in essence the same qualities a coat of tung oil has, strictly speaking in visual results.

Regardless of topcoating the oil or not, the other body has a bloodwood top. There is also 2 bloodwood strips in both 5pc necks (along with african mahogany) and one of them has extended cocobolo binding down the sides (practically a 7pc neck), binding that spans the whole width of the headstock, and a matching headplate. The other has bloodwood in almost the same manner. I'm not trying to paint a picture of the guitar for you, but I felt those features were worth mentioning because I have heard that cocobolo and other exotic woods have natural oils that prevent the proper curing of oil-based finishes (I assuming that a tung oil finish is an oil-based finish). I have heard that teak oil will cure better on such woods and can be used just as, but I have also heard that teak oil isn't a pure drying oil like tung or linseed oil due to special drying agents. In the same discussion, I have heard (I hear lots of things) of people using thinners/solvents to remove the woods own oil before applying tung oil, or any finish in general to these resinous woods. Perhaps the solvent used in thinning the first coat of oil does the same? The Finishing book reads that some sealers often used to lock in stain/filler from bleeding into can also be used to seal off the woods oil - vinyl sealer, shellac, and glue size specifically. My question is: If it can lock a woods own oil in, won't it prevent the applied oil from penetrating in as well? Basically, for this situation, I need any advice on applying an oil finish on highly resinous woods.

3. And finally, I need a way to get a super smooth finish with an oil finish. The Finishing book suggest using 600 grit to wet-sand the second coat into the wood, creating a slurry of oil and sanding dust that will make the surface smoother by helping to fill the pores. I don't was to use filler on the necks (I don't care about a perfectly leveled surface on them) nor do I want to fill the bodies with an actual pore filler. I want the look of the pores to remain intact so I intend to fill those mostly with clear lacquer and of course vinyl sealer will inevitably fill up some of the pore. Anyway, I was going to use the books method and call it a done deal until I came across a much more developed technique (titled as wet-burnishing) during my search for elusive oil finishing information. It goes something like this:

- Sand the wood to 600-800 grit, keep the last-used piece of sandpaper on hand and leave the extra-fine sanding dust in it
- Apply the oil to wood's surface (didn't mention anything about thinning, but I would still have done so)
- Once it has had a couple of minutes to soak in, use the dust-filled sandpaper to burnish the oil into the wood
- Replenish dry spots as they appear (no mention of wiping off excess at any point, but I would still have done so)
- Let the wood dry before adding successive coats
- Continue sanding the surface with 1200 grit in two or three sanding/oil combinations

Now, let me say that I suspect this process to be 1 of 2 things. Either relating to a specific application of any oil finish in general, or (and I happen to think so) being the writer's method of applying a product known as Organoil. The reason I don't know for sure is because it happens to be the only method described for application amongst all the information about oil finishes including organoil. Another thing that makes me think that the writer may use this technique for all oil finishing is that, upon looking up the homepage of this "Organoil" I noticed that their directions for applying organoil had differences, some being explictly disobeyed in the writer's "rendition".

Being that the above method doesn't deviate radically from Jeff Jewitt's method for applying pure tung oil, I am still highly inclined to use the wet-burnishing method (perhaps slightly modified based on the results I obtain), unless you can provide your way for obtaining a super-smooth finish or if you find any of the above-mentioned methods unacceptable for any reason.

Allow me to excuse myself for taking up the better part of your day with such a lengthy post, and whatever amount of time it takes to compile all the information that I've requested, but I won't remain ignorant about something important to me when such a great source of undisputed information presents itself, and I think it's rather unnecessary to learn by trial-and-error when there are those who have the experience and generosity to pass on what works. I'm not just trying to flatter you, for I've seen how everytime someone was in doubt about oil finishing you came through with the answers. So, any advice that you could provide me would be thoroughly appreciated. In truth, I only made an account on this forum to get in contact with you (I don't have an interest in replacement parts). That being said, please send your reply to my email at xxxxxx@xxx and once again, thank you for your time.

My 2c

1.  On the stain, spraying is usually not best, and wiping, rubbing and more wiping usually is.

2.  You wont "need" tung oil under lacquer to make stained wood "stand out".  Perhaps a better choice as a barrier between stain and lacquer is shellac.

3.  To get a super smooth finish - with any finish - preparation is the key.  Fill the grain, sand it smooth, make sure its completely filled, and you'll get a smooth finish.

I hope some other folks add their own responses to this as well.

Nice thing you did there CB  :icon_thumright: Really nice seeing all the experienced builders here sharing their knowledge with people who want to learn.
I think he was hoping to evoke some other responses on finishing to the thread.  Unfortunately I have nothing to add to this topic as my experience with Tung Oil pales in comparison some of the others on the board.  I also got a lot out of this post though.  :icon_biggrin:
Apologies if I wasted thread space, in terms of advice, I would just reiterate that preparation is key. A clean well ventilated area with a stable temperature is a must. Good spraying equipment although initially expensive is well worth it down the road, etc. In fact, tonar on the message boards here does many step by step finishes and provides a lot of good information. I would follow his advice quite closely as his finishes are spectacular.