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View Full Version : Shellacking the Inside of the Ukulele



sequoia
02-02-2018, 06:59 PM
I've been thinking that shellacking and finishing out the inside of the ukulele body is a good idea. Many of the high end luthiers on this forum do it so what the hell. I think this might be good idea for three reasons: 1) It provides extra protection against humidity changes in the environment in the back and sides, 2), it might give some extra acoustic volume and projection (maybe) and 3), it just looks better if you look inside the sound hole which nobody ever really does other than us builders and luthiers.

Below are some pictures of my shellacked finished insides. Next time I actually might sand. Such a concept. Also included are pictures of my "ridiculously over engineered neck block" (to quote Pete) which I'm starting to think might be a waste of effort.

106427

106428

jcalkin
02-03-2018, 03:18 AM
Reason #4: A saturating finish on the inside prevents wood varieties like big leaf maple from transfering stains to the inside of the body.

bsfloyd
02-03-2018, 03:46 AM
I'm not a luthier or builder, but I always look around the inside of my instruments. I appreciate to see the detail the builder has done, also see just how sloppy some factory builds can be. I've always wondered why the insides aren't finished. As mentioned above, it can aid for climate concerns. I am also a drummer and the higher $$ drum shells are finished inside. This also aids in sound projection, so I think the same could apply for stringed instruments.

Yours is looking fantastic!!

HogTime
02-03-2018, 06:01 AM
A very classy looking interior and neck block! :)

Michael N.
02-04-2018, 03:00 AM
I'm not convinced. Finishing the inside won't stop the instrument being subject to variations in humidity. It might slow transfer down a little but it won't stop it. There's also a downside for any possible future repairs, it just makes things more difficult.
As for the volume/projection? Pure speculation or unfounded optimism.

Beau Hannam Ukuleles
02-04-2018, 07:31 AM
Any barrier over wood will slow down the effect changes in humidity to the wood, which is beneficial in every way. This on going benefit far out ways any possible future repair needed. Besides, just sand a small area and cleat it- pretty easy.
Also, it is common work practice in furniture making (so ive read) to seal each side of, say, a table top to stabilize it.

weerpool
02-04-2018, 11:51 AM
bob taylor wasn't convinced , neither am i


I'm not convinced. Finishing the inside won't stop the instrument being subject to variations in humidity. It might slow transfer down a little but it won't stop it. There's also a downside for any possible future repairs, it just makes things more difficult.
As for the volume/projection? Pure speculation or unfounded optimism.

BlackBearUkes
02-04-2018, 06:14 PM
Repairing instruments with finish on the inside (there are very few) is not as easy as you make it sound. When I do get a guitar in for repair and I do need to go inside, many times the inside shellac finish is sticky and has collected a lot of dirt and dust. Also, I have a shop next to a guy who repairs wooden furniture, old and new and rarely are the undersides of tables finished. I personally don't see much benefit of a finish on the inside of any instrument and thankfully I don't come across it too much. Just my experience.


Any barrier over wood will slow down the effect changes in humidity to the wood, which is beneficial in every way. This on going benefit far out ways any possible future repair needed. Besides, just sand a small area and cleat it- pretty easy.
Also, it is common work practice in furniture making (so ive read) to seal each side of, say, a table top to stabilize it.

Beau Hannam Ukuleles
02-05-2018, 10:09 AM
Also, I have a shop next to a guy who repairs wooden furniture, old and new and rarely are the undersides of tables finished.

Interesting!- ill have to ask around

DPO
02-05-2018, 10:26 AM
Interesting!- ill have to ask around

I worked in a cabinet making shop in the eighties,,we rutinely sealed the underside of table tops.

Allen
02-05-2018, 10:35 AM
I've repaired and restored an aweful lot of antique furniture made from solid timber over the years. Frrom tables to wardrobes. It was almost always sealed on both sides.

I continue to do this because the old fellows that instructed me in woodworking drummed into me that what you do to one side you do to the other.

sequoia
02-05-2018, 06:18 PM
Also, I have a shop next to a guy who repairs wooden furniture, old and new and rarely are the undersides of tables finished.

I'm not a master carpenter, but when I was younger I did pass myself off as a finish carpenter because really, it ain't that hard and it is a hell of lot easter than framing on the body. The one thing I learned is that finishes are expensive and take time so the rule was, "it it don't show, it don't get finished". Makes sense. As for furniture, nobody really looks at the underside of the table, so why finish it? Perhaps this comes more from the frugality of the furniture maker than any conceived notions of how the wood is going to react to the environment?

Now as to giving the instrument a "sonic boost" (my words), I agree that this is entirely speculative, unproven and maybe even pure hooey, but my intuition (and that is all there is) says that yes, it is going to make the inside of the box more reflective and thus will have an effect. What that effect is, I don't really know. My theory is that it might make things a little brighter and quicker which may or may not be a good thing. We shall see.

BlackBearUkes
02-05-2018, 08:30 PM
I would say that about 98% of all the wooden string instruments that I have worked on over the years, that includes guitars, violins, mandolins, etc., both plucked and bowed, none have finish or sealer on the inside. Belief systems are amazing things, but they're only beliefs.

Michael N.
02-06-2018, 02:46 AM
In the late 70's there was a bit of a fashion for finishing the inside of classical guitars. I say a bit of a fashion because it really was just a few makers who were doing it - the belief being that it helped volume/projection. I think if you were to do a poll of expensive handmade classical guitars today over 95% of them would not be finished internally and classical guitar makers are a bit obsessive in respect of volume/projection. It's quite possible that a huge swathe of them have overlooked it or it doesn't do what some claim. In fact there's almost certainly much better ways of increasing volume, that is to have mass and stiffness in the back/sides - which is partly what the Smallman concept is.

Beau Hannam Ukuleles
02-06-2018, 04:26 AM
There is no benefit to mentioning the possible benefits of extra vol/projection in sealing the inside of an instrument. It just gives people fodder to dis you. Same goes with the use of Tonerites to break in an instrument.

As for why furniture makers finished (and by finished I mean simply sealed, not full on french polished) the underside of table tops when no one could see it. It wasn't a cosmetic consideration, it was a engineering principle to help minimize stop buckling, bowing caused by such a large area of wood absorbing/dissipating moisture at a fast rate.

If you don't believe in the benefits of doing this, I don't really care, but I do it because it makes logical sense.

As a test, after you put a rosette in a top, seal one side of it and watch it buckle .

Allen
02-06-2018, 09:44 AM
Exactly what Beua just said.

BlackBearUkes
02-06-2018, 11:00 AM
I do not see any possible benefits of added volume by sealing the inside of a uke or guitar. If you have some proof, I would be happy to consider the data and may even change my mind. To say, there may be possible volume increase, and use that as a selling point, is like saying "I believe this to be true, so prove it doesn't". If you can't prove it, why try to sell it.

There was some discussion years ago by a builder of classical guitars that after he was done building, he would wet his finger, add salt to it and then rub the inside top bracing to help voice the top. He swears it worked wonders. Needless to say, the discussion about this method got very heated with the lutherie community.



There is no benefit to mentioning the possible benefits of extra vol/projection in sealing the inside of an instrument. It just gives people fodder to dis you. Same goes with the use of Tonerites to break in an instrument.

As for why furniture makers finished (and by finished I mean simply sealed, not full on french polished) the underside of table tops when no one could see it. It wasn't a cosmetic consideration, it was a engineering principle to help minimize stop buckling, bowing caused by such a large area of wood absorbing/dissipating moisture at a fast rate.

If you don't believe in the benefits of doing this, I don't really care, but I do it because it makes logical sense.

As a test, after you put a rosette in a top, seal one side of it and watch it buckle .

Beau Hannam Ukuleles
02-06-2018, 12:42 PM
I never claimed it added volume or anything other than climate control.

I do think it logical to say that an inside that has small pores (or no pores like maple) and is smooth reflects better than an inside of a wood with large pores and sanded to 80 grit.

I don't go the extra step of grain filling the inside before shellacing it but it would seem logical to assume it would add something (perhaps only a computer would be able to hear it, i dont know...but the principle is a logical one)

sequoia
02-06-2018, 08:20 PM
I do not see any possible benefits of added volume by sealing the inside of a uke or guitar. If you have some proof, I would be happy to consider the data and may even change my mind. To say, there may be possible volume increase, and use that as a selling point, is like saying "I believe this to be true, so prove it doesn't". If you can't prove it, why try to sell it.

There was some discussion years ago by a builder of classical guitars that after he was done building, he would wet his finger, add salt to it and then rub the inside top bracing to help voice the top. He swears it worked wonders. Needless to say, the discussion about this method got very heated with the lutherie community.

OK. I hear you. But by saying the old luthiers didn't do it doesn't really answer the question. I do not assert that it adds moisture protection (unproven), increased volume or sustain (unproven) or aesthetics to the instrument, however, what are the downsides? In other words, it might not help, but it certainly don't hurt neither. And just because that nobody did it before is not an argument. What is your experience Doug? Have you tried it?

Beau Hannam Ukuleles
02-07-2018, 06:26 AM
I do not assert that it adds moisture protection (unproven),

Actually, that's proven. Shellac isn't a great barrier (as good as say poly, etc) but is a barrier, which mitigates moisture to and fro, however small.

BlackBearUkes
02-07-2018, 10:32 AM
There are two issues that are most problematic to me. First, is the shellac sealer gets too warm or moist from its environment, it will collect dust and dirt and hold on to it, I've seen this a couple of times on some repair work. Second, if a crack develops that needs to be repaired from the inside, often times trying to sand finish away from that area is very difficult if not impossible.


OK. I hear you. But by saying the old luthiers didn't do it doesn't really answer the question. I do not assert that it adds moisture protection (unproven), increased volume or sustain (unproven) or aesthetics to the instrument, however, what are the downsides? In other words, it might not help, but it certainly don't hurt neither. And just because that nobody did it before is not an argument. What is your experience Doug? Have you tried it?

sequoia
02-07-2018, 06:18 PM
There are two issues that are most problematic to me. First, is the shellac sealer gets too warm or moist from its environment, it will collect dust and dirt and hold on to it, I've seen this a couple of times on some repair work. Second, if a crack develops that needs to be repaired from the inside, often times trying to sand finish away from that area is very difficult if not impossible.

Good fresh shellac should not get gummy at anytime regardless of moisture and heat. What I think you might have seen was expired shellac which does not cure correctly and indeed you would see gummy shellac that attracts dust and dirt. Here is what might have happened: The luthier has some old shellac and he thinks, hey I'll use this old stuff on the inside cause it won't show.... I think your second point is more valid. Yes for sure repair work will be more difficult while trying to glue cleats, etc. or whatever to shellaced wood. Someone pointed out that you can always scrap the shellac away before gluing but this could be problematic due to the awkwardness of the repair site and shellac penetrates deep into the wood making scraping possibly ineffective. In such situation I would consider using the nuclear option: Cyanoacrylate. But good luck trying to repair the repair.

In my opinion the positives outweigh the negatives in this case.