Mandolin back and sides?

[Willie Poole]

I am wondering if having the back and sides on the inside of a mandolin unfinished will absorb and kill some of the loudness of the instrument? Do any of you builders put a coat of varnish or lacquer on the backs and/or sides in side of the instrument? Many years ago I had an Aria that seemed to have the inside of the back sprayed with lacquer and it was a good sounding mandolin....I know that banjo players usually have the inside of the resonator sprayed with some kind of usually hard finish, I assume to get the sound to "bounce' outward...

Willie

[Bob Clark]

The late Walt Kuhlman of Gypsy's Music used to finish the insides of his instruments. Might be more accurate to say he sealed them. I don't know how it impacted the sound, but the mandolin I had from him was pretty nice.

[NRMiller1958]

I seal the inside of my instruments, mostly to moderate changes in humidity. I want both the inside and outside to adsorb humidity at a similar rate.

[MikeEdgerton]

Yamaha back in the 60's was finishing both the inside and outside of their guitars, I have one. They stopped doing it before I bought my last Yamaha in the 90's. I'm going to go out on a limb here and say there's a reason that Martin, Gibson, and most of the other manufacturers and builders don't finish the inside of their instruments.

[Tom Haywood]

Yamaha back in the 60's was finishing both the inside and outside of their guitars, I have one. They stopped doing it before I bought my last Yamaha in the 90's. I'm going to go out on a limb here and say there's a reason that Martin, Gibson, and most of the other manufacturers and builders don't finish the inside of their instruments.

I just picked up a Yamaha red label guitar, approx. 1969. The inside back and sides are sealed in a thick coat of what appears to be shellac, with a thin very thin coat inside the top. These tend to be pretty good and loud guitars.

Considering that the early 20th century mandolins were not sealed inside and so many of them are still in good shape, I don't see a need for that kind of protection. More sealant will likely take some flexibility out of the wood. No telling what changes that might make to any given instrument.

[HoGo]

Sound is not like tennis ball it doesn't bounce around the inside. It is the changes of air pressure inside or at the outside surface of instrument.
Sealing inside may help seasonal stability but no finish is perfectly waterproof so it only slows down humidity transfer. Finish adds weigth and that kills tone, so anything thick will not be good and it won't (contrary to popular belief) add any strength.
The wors thing is that it may be more costly to repair such instrument when cleating is necessary...
There's nothing wrong with bare wood inside... If it ain't broke...

[multidon]

When Walt Kuhlman was still with us I discussed at length with him his building philosophies while pursuing a possible octave mandolin build. So this is straight from the horse’s mouth, so to speak. When I brought up his technique of sealing the inside surfaces of the instrument with shellac, he told me this was a “Old World” technique he learned from European Luthiers, and its purpose was to help stabilize the instrument against humidity changes. That was it. Nothing about enhancing tone or anything like that.

[j. condino]

You basically have two components to the conversation:

1- sealing the wood to stabilize humidity variations

2- dealing with how much it sucks to do simple repairs because nothing will stick to the finished inside surface...

I used to seal the insides of my guitars about 25 years ago. Then I had to do some repair work on one of them in an area where I could not reach it. After a LOT of cussing and a very long frustrating repair that I had to do several times because nothing would adhere to that inside finish, that was the last one I ever finished on the inside.

[Mark Gunter]

Speaking strictly as a curious thinker, not as a luthier or scientist, my imagination says that any worry about the top plate, back or ribs of an instrument "absorbing or killing sound" would be misplaced worry. Since these elements are supposed to vibrate in order to produce sound, exciting these elements (via "absorption" of sound waves) would only enhance the vibratory function, it would seem to me. But, I think it's unlikely that in most cases it would make a very big difference, especially if you're just sealing the inner surface with a light seal coat.

As a wood finisher and repair tech, I tend to agree that sealing the surface could make repairs more difficult if a cleat is needed in there.

Maybe someone who knows the science could educate me on the other matter, "absorption of the loudness" - till then I can only go with my imagination, that's worrying about the wrong thing. Species of wood, stiffness of wood, dimensions of the carved top (esp. recurve) would be way more important than an interior seal coat, I'd wager.

[Ivan Kelsall]

Hi Willie - The insides of banjo resonators 'come as they are' from any single builder. The resonator on my Stelling is finished in some type of lacquer,but the wood itself hasn't been sanded perfectly smooth. I suspect that the finish has more to do with protection from dirt & moisture than anything,
Ivan

[HoGo]

Hi Willie - The insides of banjo resonators 'come as they are' from any single builder. The resonator on my Stelling is finished in some type of lacquer,but the wood itself hasn't been sanded perfectly smooth. I suspect that the finish has more to do with protection from dirt & moisture than anything,
Ivan

So they can double as salad bowls...

[Jess L.]

I seal the inside of my instruments, mostly to moderate changes in humidity. I want both the inside and outside to adsorb humidity at a similar rate.

Seems sensible.

[Jess L.]

Yamaha back in the 60's was finishing both the inside and outside of their guitars, I have one. They stopped doing it before I bought my last Yamaha in the 90's. I'm going to go out on a limb here and say there's a reason that Martin, Gibson, and most of the other manufacturers and builders don't finish the inside of their instruments.

Planned obsolescence, maybe? Martin, Gibson etc might not want instruments to last too many decades without acquiring cracks/etc (drying out too fast due to unsealed inside???) that might prompt an owner to say "the heck with it" and just run out and buy a new one, thus helping to keep the factory in business...

Edited to add: Oops, I hadn't read all the posts before replying. See below.

[Jess L.]

... dealing with how much it sucks to do simple repairs because nothing will stick to the finished inside surface...

I used to seal the insides of my guitars about 25 years ago. Then I had to do some repair work on one of them in an area where I could not reach it. After a LOT of cussing and a very long frustrating repair that I had to do several times because nothing would adhere to that inside finish, that was the last one I ever finished on the inside.

Ah. Now that's an interesting angle, and it sounds like a serious concern. I hadn't thought of that...

[John Kelly]

Interesting discussion. I have at the moment a coupe of fiddles I am working on, both over 100 years old and no sealant/finish anywhere inside them. Nor have any of the other fiddles I have seen with their backs or soundboards off. Usually there is some varnish run around the insides of the f-holes, but nothing else. When I opened up those two they both had years of accumulated debris and muck and one had a couple of the "dust bunnies" mentioned recently in another thread here in this forum. If instruments as lightly built as fiddles can survive without internal sealants/finishes then I imagine that the luthiers did not see any heed to apply any internal finish. The fiddle also seems never to lack in volume, though a lot of this is due to its construction with carved top and only one tone bar.

[William Smith]

Well with that we could go into why Martin sprayed finish over the guitar with the pickguard already on them, hence the guard shrinking-the dreaded B-string top crack that are on so many old Martin's.

[j. condino]

Martin attached the pickguard using acetone to melt the plastic directly on to the raw wood, so they had to spray finish after. That is why you get the B string crack, not because of finish over the top of the pickguard. I'll still take that over the current dot matrix looking printed pickguards that are taped on....

[Willie Poole]

Some interesting points ...The reason why I asked this question is that I always figured the reason for a coated/sealed resonator on a banjo was to make the sound "bounce" back to the front of the instrument, if the wood was bare I figured it would absorb some of the sound ....

Many, many years ago I owned a `40`s Gibson A-50 mandolin and if you folks remember the floor polishing product called "Future", it was sort of liquid plastic, any way I coated the back of that A-50 with it and for a week or so the mandolin sounded dead but soon after it all dried 100% it really seemed to get louder and louder and it sounded so good that a fellow offered me a small bass boat with a small motor in trade and I already had another mandolin so I made the trade but never followed up on what happened to that mandolin, I do know that the fellow moved to Alabama and I never heard from him after that...

Thanks for all of the interesting comments....

Willie

[printer2]

If anyone was to finish the inside shellac would be the best thing as it is easily removed with alcohol in case you ever need an instrument repaired. On the downside, any finish thin enough is not going to stop humidity from being absorbed in the wood. Also the thickness of the wood is thin enough that the moisture quickly migrates through the wood.

[MikeEdgerton]

... I'll still take that over the current dot matrix looking printed pickguards that are taped on....

Amen.