Finishing with varnish.

I did wood work in highschool (last year) and finished furniture so varnish/lacquering wood isn't really all that new to me. But since musical instruments aren't furniture, I'll ask here, how many coats of varnish would start to dampen the sound?

I'm currently mixing an estimate of 50% varnish and 50% methylated spirits so each coat should be relatively thin - I'm on my second coat now. The reason that I'm doing this is so that I can seal the pores, making it into those full gloss instruments.

Are you using instrument lacquer? I'm not sure what is in it that is different from regular lacquer, but I believe it's less likely to crack.

Unfortunately, no, I'm not, I'm using 'british paint' branded varnish. If you're referring to cracking due to extreme temperatures, Australia's temperature is pretty alright (both temperature and humidity wise) so I don't think that will be a problem...Unless I leave it out in the sun.

be sure it is not a 'spar' type varnish, as they are meant to stay soft (...read, 'sound damping') to remain flexible in extreme changing weather. How you brush it will affect the thickness of the film. My background is in finishing. I finished my first instrument in lacquer, too thickly. It looked great... After a month or so of playing, and suspecting that the finish was too thick, because the sound was too 'closed up', and constrained, I unstrung it and carefully cut back the finish starting with 1000 grit, front and back, cutting, polishing, re-evaluating, cutting some more. Then I polished it back up to gloss. The change in sound was immediate, my teacher recognized it too. Now the finish on that instrument is fully cured, it has 'opened up' even more. I suspect that part of the 'playing in' of a new instrument, is the finish curing, in addition to the changes in wood, and the 'settling together' of all parts, and aspects of it. Now my attitude is to get the wood as smooth as possible prior to finishing, and put on the minimum finish to protect the wood. At this point in the game, I will err on the side of not enough finish, and watch for failures. The intention of the instrument is to make beautiful sound, not to last forever...



You did not mention what you are doing for grain filling? that will affect what you need for the finish thickness. Also, the viscosity of the finish before thinning. At 100% thinning, (50/50 as you say) 3 coats might be enough, maybe 4. With varnish applied that way, I would be wetsanding with at least 400, carefully wiping off ALL residue after. For an instrument, I would probably wait at least a day between coats.

Not exactly sure about whether it's a 'spar' type or not.

I'm not 100% with the wood work jargon but you mean grain filling as in filling the pores, right? Sorry, my teacher didn't really go indepth with the jargon and stuff. Anyway, I researched about it (before I started varnishing it) and it said thinned out lacquer (around 50 - 60% mineral spirits) would be able to fill/seal the pores so I'm just going with that.

My second coat was applied with a piece of cloth rather than a brush this time, just to test out whether the cloth would be better. Has anyone ever tried this? The second coat seems to be pretty thin from using the cloth which should be a good thing, shouldnt it?

Thank you for the help by the way!

Bao said:

Not exactly sure about whether it's a 'spar' type or not.

I'm not 100% with the wood work jargon but you mean grain filling as in filling the pores, right? Sorry, my teacher didn't really go indepth with the jargon and stuff. Anyway, I researched about it (before I started varnishing it) and it said thinned out lacquer (around 50 - 60% mineral spirits) would be able to fill/seal the pores so I'm just going with that.

My second coat was applied with a piece of cloth rather than a brush this time, just to test out whether the cloth would be better. Has anyone ever tried this? The second coat seems to be pretty thin from using the cloth which should be a good thing, shouldnt it?

Thank you for the help by the way!

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Read the label of the varnish. Is it oil based varnish, resin based or acrylic based?

Traditionally, the term "varnish" is fairly specific, though it covers a wide range of exact formulas. "Varnish" is made from a drying oil, typically linseed, tung, or spike (lavender), with one or more resins which can dissolve in an oil compatible thinner...usually mineral spirits or turpentine. suspended in the oil. In other words, drying oil + resin(s) = varnish. So all varnishes are oil based with resins. The most common resins are alkyd and phenolic.

Except when you're talking about "spirit varnishes"...which are shellac + resin(s) which will dissolve in alcohol. Behlen's violin varnish is a spirit varnish.

Oil varnishes are roughly divided up into "long oil" varnishes which have a higher percentage of oil (think Waterlox...which, of course and confusingly is sold as an oil finish) and "short oil" varnishes which have a higher resin content and lower oil content.

And then we find that some "oils" are actually varnishes, and now with the use of urethane resins, it gets really confusing.

Spar varnishes tend to be long oil and are thus more flexible. They also have a fair amount of UV inhibitors in them to protect yacht brightwork from sun.

And now there are acrylic varnishes, water borne varnishes...you name it. Varnish has become a very generic term pretty much covering anything that is a clear thin finish.

So...if you're talking here about "varnish"...well, what is it? Unfortunately, you can't just say "varnish" and have it mean much

And look into Epifanes products; they have excellent oil varnishes some of which have been used very successfully on instruments.

One other point: by proper definition, TruOil cannot be considered a "varnish" because, at least according to the listed ingredients, there are no dissolved or suspended resins in the formula.

Personally I wouldn't try using shellac or any other kind of finish as a pore filler. I'd use a product specifically designed for filling pores; there are plenty of them out there, some better than others. As a "sticker" coat however, or a finish by itself, shellac can be wonderful.
And I'll also be contrary in stating that for me building a good sounding instrument is only one (out of a handful) of my objectives in building. It also has to last a good long time (although perhaps not forever.) The most beautiful sounding instruments often don't last long.

That's the dilemma Chuck isn't it? Form over function and stuff....

Pete Howlett said:

That's the dilemma Chuck isn't it? Form over function and stuff....

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Form, function, longevity, playability, price...... it's all a balancing act.

In my 25+ years of professional finishing, I have always aimed to leave a finish that is as durable as possible, and as beautiful as possible for the given situation, finding that balance. Finishing an instrument adds a new twist, at least one.... I have confirmed that too much finish will kill the sound. As I am not yet selling my ukes, I am willing to learn what is 'enough' finish, I am willing to see a little failure. There is enough work involved with making one that I want them to last, but I also want to explore how to build and finish them well. As a consumer, I would want an instrument that is not going to wear through immediately, or fail prematurely for whatever reason, especially with a top notch boutique one. For my own instruments, I will build them, and ride them hard to see what does not work, and what does.

When I start selling ukes, I do not want to see returns, so the finish will be 'enough' and maybe slightly more, will have to see..

Chris_H said:

be sure it is not a 'spar' type varnish, as they are meant to stay soft (...read, 'sound damping') to remain flexible in extreme changing weather. .

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People use KTM-SV to finish instruments.

In Cali, lots of restrictions to using Nitro, maybe that's why many use Poly finish or out source. I think some of the individual luthiers use nitro but don't know if they follow all the govt guidelines.

Oohh, it's oil based.
I've never seen the word 'spar' used while I was researhing, maybe i didn't do enough LOL

The "restrictions" on nitro are highly over-stated here in California. It depends on which air pollution control area you're in and how much a day you intend to spray. We can and do shoot nitro here and so does Santa Cruz Guitars...to the tune of about 60 guitars month over at Richard's shop. There are probably twenty nitro instruments going through my booth (being done by Addam Stark) a month plus my twenty or so in poly.

Hey everyone, I've finished applying the varnish and am now just waiting for it to fully cure. All 3 of my coats have been thinned out individually before I applied each. I've got 2 questions before I can start rubbing out the finish.
1. How long would it take to cure until we can polish up the uke? I assume it will be a little quicker than usual since all 3 coats were thinned out.
2. If I were to reinstall the strings, would playing the instrument disturb the curing process (due to heat and all that)?

Thank you in advance!

3 coats? Probably should be more like 6 or 7 if you thinned properly...

I wouldn't say it's proper, it was mainly estimations of the mineral spirits added in, ranging from 30% to 50%. I should but I'm worried about dampening the sound. If I accidentally rub through the finish on the uke, I've got plenty of time to add more coats since I'm on my holidays still.

If this is your first time finishing an instrument, the probability is very high that you will sand or polish through the finish. Listen to Rick and apply at least three more coats before curing for at least a week.

mzuch said:

If this is your first time finishing an instrument, the probability is very high that you will sand or polish through the finish. Listen to Rick and apply at least three more coats before curing for at least a week.

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What he said. I found that to be an easy mistake to make