Finishing Both Sides

[ToneMonkey]

I was thinking the other day, I could tell it was thinking as I started feeling dizzy.

When acoustics are finished, why is the finish only applied to the outside. Does the wood want to be completetly sealed, or is it right to have one half of the wood (the inside) open to the elements?

It would also give a smoother finish on the inside, and could possibly increase the reflected sound waves inside the guitar (although the trade off would be less resonance of the wood itself due to the finish)

Anyway, just a thought. What do you guys think?

[Daniel Sorbera]

Lots of custom builders spray on a quick coat of shellac on the inside to seal things.

[jammy]

This has recently been discussed over on the OLF

http://www.luthiersforum.com/forum/viewtop...t=finish+inside

[ToddW]

Good discussion over there. What they don't mention, is that of all the common finishes, shellac is one of the best water vapor seals. Flexner's finishing book is great for details like that. So shellac will slow down the woods adjustment to humidity changes better than most other finishes at a given thickness, even though it isn't the most water resistant.

When I finally get around to building an acoustic, I plan to finish the inside with shellac. I even shellac'd the inside of the sound chambers on the solid body I'm working on now. I put too much time into these things to ever want to see them split/warp/crack because I figured humidity protection wasn't worth it. Course I'm also in NC, so the humidity difference between inside with AC and outside can get pretty huge, and winters get pretty dry despite a home humidifier. My piano has its own humidifier/dehumidifier system so I don't have to worry about it, but my guitars don't.

Todd

[fryovanni]

I have added a quick coat of shellac to the interior and I have done it without. Really there is little difference from what I can tell. That would be expected though, because the only thing a finish is going to do as far as the effects of humidity changes is slow the process a bit. If you don't subject a guitar to radical changes in humidity it will never make much difference. If keep your acoustic in its case then go out and play for a few hours(potentially outdoor events or what have you), then it may slow unwanted changes over than short haul. If there is an advantage I suspect that would be it.

It is more work. Some customers would view it as "not traditional", although few would consider unfinshed as such. For those reasons there is little advantage to a builder to finish the inside of a guitar. Functionally the potential to do harm seems slight(a light coat of shellac has little effect on the shape of the surface, weight or stiffness). The potential for benifit will occur only under conditions that are extream, and short in duration(something we try to limit from happening, so this benifit may not be seen by most users).

That is my take on the subject, FWIW.

Rich

[MiKro]

Todd,

Funny that you say your Piano has a dehumidifier. My Grandparents lived in Greensboro NC, they bought a wonderful Steinway baby grand in 1959. I became the owner of same in 1983. when I went to bring it home the soundboard was cracked. Why, because of the humidity changes in NC ( it had a humidifier installed by the Steinway company they purchased it from). I was told that moving it to Texas would be very BAD!! (by the Steinway Dealer). I sold it back to the Steinway dealer in Greensboro. I wish now I hadn't done that, but what would it have cost me to fix it? Who knows? Lesson learned, even the dehumidifiers and whatever are not all they're cracked up to be. Be your own judge, WATCH and LEARN from the WOOD. It will tell you what it needs, if you look and listen.

Just some peaceful advice and wisdom for what it's worth!

Mike

Edited May 1, 2008 by MiKro