Official Luthiers Forum!

Can someone help in answering this non talked about subject of french polishing or epoxing the inside tops and backs of acoustic guitars, if this proceedure is used by any of the pro luthiers, what are the advantages and disadvantages and effects on sound ect ? hope Im not the only member intrerested in this subject.

Rookie

First, welcome to the forum. It's a great place. As for your question, if you search on "finishing inside," you'll find this comes up often. There are pictures of guitars whose insides are better looking than the outsides of mine. Some builders do it, but I think you'll find most do not. Looks really cool though.

Mike

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Mike Lindstrom

As my guitars got very light I started applying a coat of shellac in them, but I don't any more.

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Brock Poling
Columbus, Ohio
http://www.polingguitars.com

Not a pro, but I'll share what I've heard here and in other places (Ervin Somogyi puts a coat on the inside of his guitars)

It's my understanding that it's mostly an issue of cosmetics - "wow. look at the shiny insides of that guitar", although some believe that a coat of shellac can slow the impact of changes in humidity on an acoustic guitar, which makes some sense to me.

But that's "a coat" of shellac, not french polishing, which could take days, if not weeks.

I've put a coat on the inside of a couple of guitars, and I think it looks cool, but be careful of rosewoods and some other woods - the alcohol can act as a solvent for the pigments in the wood and cause them to bleed, which doesn't look so cool

As Corky stated the only real advantage is in humidity protection. Most that add shellac to the inside do not french polish. most will brush or lightly pad. To French polish the inside is a pain but more than doable. I have done so on a few but only by request.

Not really relating to finishing, but some builders (Larrivee and others) believe that having the inside of the guitar 'too smooth' is detrimental to the sound. So getting the guitar interior 'ready' for finish may have an effect by itself.
Just another idea in the mix.

John

There is a Scottish guy who does a few lessons on Youtube who does a "perfect" French Polish finish on the inside (by perfect I mean as good as the outside of his guitars). His reason was that as a former furniture maker, the thought of leaving wood unfinished was awful to him.

i am no expert by any means but i would tend to think the exact opposite. the smoother and more solid a surface is the better reflection or reverberation of sound. thats why sound proof rooms are built with foam padding as the last layer. a very non dense, porous, and uneven surfaces catches sound almost and lets it dissipate into itself, instead of taking that sound wave and pushing it right back out the sound hole. all that being said im sure there's a certain break point where someone may not like the sound coming from a ready for finish guitar. i have seen many Gibson and older guitars that are completely rough sawn braces and not very finished inner surfaces and people have been loving these guitars for decades.

I have "sealed" the interior of about the last 90 guitars I have built and will continue to do so. It retards moisture exchange and it also changes the stiffness of the wood that it is applied to.

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tim...
http://www.mcknightguitars.com

I seal the inside of all of mine.

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Allen R. McFarlen
Barron River Guitars & Ukuleles
Facebook
Cairns, Australia

Yea I have seen the youtube posting on his work. Great job but a lot of work that is really just for apperance. other than the added moisture control. I think there was a post on it here not too long ago.

Thin coating for protection?- sure. Hard glassy finish? -not for me. You'll most likely have sound waves reflecting all around in possibly unfavorable ways.

I merely put enough on to seal the inside, and that's not even a finishing Shellac, it's a brushable sealing Shellac which dries to a satin, I brush a coat on and while its still wet, wipe off the excess. The words of Bob Benedetto ring in my ears, "Do to the inside what you do to the outside, why seal only one side of a board if you expect it to stay flat?" (not the exact phrase but words to the same effect ) It's merely for, as others have stated, moisture control of the wood in my instance.

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Nick Oliver

http://www.oliver-guitars.com

On a related note if you do repair and restoration work as I do you will appreciate a guitar with some shellac inside of it when it is brought to you for repair and someone some time ago has barfed in the guitar...... The chunks are much easier to remove when the inside is finished....

Oh yeah and sorry for the temporary high-jack here but doing repair and restoration work is absolutely wonderful work, a very worthy endeavor, and a fantastic way to learn much more about guitars, their realities, and what construction methods work and don't work.

I apprentice in a busy college town guitar shop and I work with a Master Luthier - the real deal. I don't get paid money nor would I really want to but I do get what I consider priceless knowledge and experience and as such I love doing this.

Yesterday I started a project where I am bringing back to life two approximately 1930's era archtops that are currently not functional. I actually get excited about working on these wonderful old instruments.

I think that the point that I really want to make here is that I am willing to do what it takes to learn. The opportunity to apprentice is often not available to old dudes like me since we may not live long enough to be able to repay the Luthier with productivity. So I am honored, humbled, focused, and fortunate to have this opportunity chunks or not.

When you finish the inside - do you also finish the inside of the soundboard before putting it on ?

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It's this new idea from recent decades that everyone gets a participation award. - MUX

John,

Yes you finish the inside of the soundboard too. Just be sure you leave the area which will be glued to the linings etc. raw so glue will stick. I'm sure you figured that out but just thought I'd mention it.

Steve

Great to hear Filippo and are you apprenticing in guitar repair at a shop with a Luthier - you didn't say what your apprenticeship was in and I am curious?

For me this endeavor started because of Rick Turner who advocated that we all learn as much as we can about guitar repair. As you may know Rick has a heavy repair background.

I've learned that repair is invaluable for builders because it gives us a glimpse of why and how guitars fail and what we as builders may do to contribute to or prevent these failures.

I'm laughing too because in my case one of the things that I had to learn was that "it's just a guitar..." What I mean by this was that I was rightly so accused of being way to careful around other people's instruments and that the ordinary care standard would require me to loosen up and chill out a bit.... Once I got over being scared to death that I would damage something it's great to just go into the shop, have a bagel and OJ while talking with David and then dive into a fret job or two. Right now I am doing two fret jobs at the same time since they both will require the same operations.

I now do repairs in my own shop too and enjoy this as much as building. One of the things that I actually enjoy more about repair than building is that the defined beginning and end usually don't have 120 -150 hours in between them..... Or in other words it is far quicker to repair most anything on a guitar, most of the time..., than to build a new one. If one looses attention easily, and I do...., this can be a welcomed thing.

I think that every builder should explore the possibility of apprenticing in repair with a real-deal Luthier. These opportunities may be hard to find but they will pay off for you big time in increasing your knowledge and confidence.

I don't do finish on inside. I guess because shops worked in didn't do it and no one talked much about it.

What Hesh said about apprenticeships is right on. I have worked for 2 shops for a total of about 3 years. Working with Bill Moll, now there is going to college. I didn't get paid in money and tell truth could never pay him enough for what have been taught. In repair, building, client relationship, working and talking with other top notch builders etc. We may be the lucky ones in we didn't need the pay and had someone who is willing to take us in and work with us. Bill is my mentor, teacher, friend and can never express how grateful to be his friend. For me working in 1 man shop is better than production shop. Learned a bunch in both, but Bill gives a lot of one on one.

I buy "project" guitars on occasion and fix whatever is wrong and have apply what have learned. Suggest a good way to go. You don't mess up a good instrument and can do things over. Re tops, neck fixes, setup/s whatever. Might see how that one sounds in good repair and then apply finish to inside and make up your own mind. Do that to several and log it. Repair is very fun and personally at times like doing that more than build. Get a whole bunch of idea's in building. Mainly what and how to fix things goof up in build. Bill's saying mess it up fix it and make money. Break it and throw it away, throwing money away, not a great way to make income, and learn nothing. He at times not real diplomatic, but that is fine, one gets the idea fast