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What are your thoughts on the effect on ageing when putting sealer inside of the box? I would think it would slow it down.How much, i couldn't say.With this said,I leave mine bare wood inside so the pores stay open for maximum ageing speed.What's your thoughts on this?

I am a firm believer in natural selection when it comes to building techniques. I have seen this done a few times and to be honest the guitars that were finished inside were less the stellar in sound. I do not see any real advantage to this practice. It will add mass to something we don't want to add mass to. This will also make future internal repairs difficult . Had this been a good thing I am sure you would have seem more of it done . Just my 2 cents.

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John Hall
blues creek guitars
Authorized CF Martin Repair
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I don't build a finish on the inside of my guitars but I do seal the inside with a coat of shellac. I left my first few bare but I have no plans to go back. The main advantage (at least for me) is that the guitar moves less with sudden changes in humidity, etc. (or at least MUCH more slowly). The difference is very noticeable: if I take one of my guitars that is unfinished inside out of the humidity-controlled area of my house I invariable have to retune at least the G string. With the inside sealed, doesn't seem to be an issue. In my book be ing less vulnerable to the elements is a good thing. As for tone, a wash coat of shellac makes absolutely no difference as far as I can tell. Just for the record I'm building classicals here but I would assume the same would be true for steel-strings.
As far as aging goes, If the guitar is being played regularly the top should loosen up a bit and the instrument should open up regardless of whether the inside is sealed or not.
-William

Sometimes I do, sometimes I don't - depends on how I'm feeling that day. A few wash coats of shellac is all I would ever put on. I agree with William that it mitigates some of the wood movement caused by changes in humidity. When I worked at Ervin's shop, all the guitars had a couple of wash coats of shellac on the inside...

Good enough for Ervin, good enough for me...

-Mark

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I have no personal opinion, but my Khono has some kind of interior finish on the back and sides.

I did notice that Ervin does it, in his book. I was, somewhat, surprised, given the view, relative to repairs being more difficult.

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I'd have to say that repairs are only moderately more difficult - the small amount of shellac that is applied is easily removed, with a little scraping and some alcohol...

-Mark

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John I'm not sure I agree with the idea that if a practice is a good thing to do that we would have seen more of it done. Are you speaking of fa*tory guitars? If so the process engineering when mass producing goods often has considerations that may conflict with doing all that can be done to make the best product possible.... Instead profitability and reducing labor intensive steps not to mention avoiding warranty claims are going to weigh heavy when considering mass produced guitars.

I was just in this discussion/argument yesterday with two other builders. My position, the minority point of view...., was that adding a shellac coat to the inside of the box added no value and I also believed that it would make repairs more complex. The other builders won the argument and in the end I was convinced that adding a seal coat to the inside of the box is not a bad idea.

Certainly Ervin has his reasons and as mentioned by Mark it really does not make repairs much more difficult at all when you consider how easily shellac can be removed AND we all remember that anything that needs to be re-glued anyway needs to have it's mating surfaces cleaned up prior to re-gluing.

What sold me is the notion that William is offering and that is that anything that does not impact tone but does slow the ravages of rapid RH changes is a good thing. It's 20F here in Michigan right now and I just returned from a buddy's house with a Heshtone in a case..... I'm always very nervous subjecting guitars, any guitars to rapid temp and RH changes so any help that we can get here is a good thing. Even though I have never used shellac before on the inside of my boxes this old dog is about to learn a new trick.

I can tell you that of the big name builders I know , they don't see and advantage to it . I know I won't do it or buy a guitar with it done. It is a personal choice and I choose not to do it. I see no advantage to it at all, No one that argues the point had any good points from an engineering point of view that can convince me it .

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John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

I tried but couldn't fit my spray gun inside the guitar


Seriously, I don't think a little shellac would hurt anything, but I don't do it.

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What about just a little bit of tung oil, just to protect from humidity?

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Francis Richer, Montréal
Les Guitares F&M Guitars

As others have said, it does slow down water exchange. A coat of shellac adds very little weight. Would you worry about 1 extra coat of sealer on the outside? There are zero issues with making repairs more difficult. Wouldn't you sand before putting in a cleat anyway?



I wouldn't put oil inside the box. That really would make repairs more difficult.

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I don't do it. A well cared for instrument is just fine without finish inside.
Tung oil? Ah, no...

Benedetto seals the inside of his archtops as well. I like it just because it makes curly maple look cool in the interior

Oil is not effective at slowing moisture exchange. Shellac is effective.

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Todd Rose
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Mark, I haven't used any finish in mine. Guess I don't really have a reason other than I think they look fine raw. Personally, I believe the end grain is where the most concern should be. If the end grain is sealed, I would think the surface area wouldn't absorb moisture particularly fast even if unfinished. Could be wrong, but based on my experience, makes sense.

Ken

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there is no benefit to putting a finish to the inside. You are adding mass where you don't want it . Also at some point you may need to do a repair on the guitar , and finish on the inside will need to be removed in some cases to to the repair.
Of the few guitars that I did see with finish on the inside they sounded dead. If you want to put finish on the inside , go ahead , there is no reason to. You would do more good for the guitar to keep it in the case when you are not playing it and keep it from RH and temp shock.

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John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

I don't put it on the inside because i feel it's a tone killer as all finishes are.And because it's not needed to protect the guitar which the outside finish is there for. It would just slow down the ageing process which i find desireable for tone.

Greetings, to put in my thoughts i think that bluescreek has been misled in his thinking that a guitar that is built very light is a guitar that will sound good. the only part of a guitar that really generates sound is the top, the back and sides have little effect. when you pluck a string on a guitar the vibrations are taken from the string into the guitar via the bridge, then they are reverberated around the body of the guitar in different physical shapes depending on the note, then amplified by the top. if you make your back and sides light then the vibrations from the string will be soaked up into them and because you are normally holding the guitar in your lap, the vibrations are killed. if your back and sides are built as solid as you can make them they will not pick up the vibrations from the strings as easily and rebound the vibration back into the room making the guitar louder for the audience.

therefor a bit of shellac, i think would only benefit the guitar. but i do not put it on the top on the inside as that would kill sound only on the back and sides.

Gypsy Bear Guitars.

My experience is with classicals so I can't really speak about steel string guitars in this respect and I don't have as much experience as some members of the forum (playing/examining guitars for 15+ years and building at a slow pace for about 6yrs) but of the MANY high end classical guitars that I've examined I'd say about half have had at least a wash coat inside, including guitars by guys that even you steel string guys out there would recognize like Fleta. Some even build a finish inside (though I'm not a proponent of that).

The weight of a wash coat of shellac is basically negligible and has, as I stated before, a negligible effect on tone (or maybe my ears aren't sensitive enough).
As for avoiding RH shock...well, that's really not being very realistic-at least in most parts of the country: Many (if not most) folks aren't only playing at home and most places aren't humidity controlled. You have to take your guitar out of the case to play it and if your playing for a couple hours in 20% humidity (which is not unrealistic when it's below freezing outside and the heat is cranked up inside-in your buddy's house or the venue your playing).
True enough, a well-cared-for guitar may not experience long-term negative effects from these short exposures to humidity extremes but my view is, "why take a chance."
Also retuning in these conditions is a bit of an annoyance. If, for example, I take my 40 year old Martin 00-28 nylon string (my first guitar-lucky me) up to the top floor of my house right now, which isn't humidity controlled and play for an hour I'd have to retune about three times to compensate for the guitar's movement from the current extremly low humidity. Roughly the same is true for the other guitars I have with no sealer inside. This is not at all true for my guitars that have a wash coat inside.

As for repairability, as mentioned, the glue surface has to be prepared anyway. Very little effect on ease of repairs.

As for "aging," again as I mentioned before, from what I've seen for a guitar that is played regularly, the top will loosen and the instrument will open up just as fast with the inside sealed. The only way I can see it "slowing down aging" is if by "aging" you mean you haven't used properly dried and seasoned wood in which case you may have some other problems.

I do build guitars professionally and have over 100 built. I am not a hack . Building a heavy guitar is not a good thing , and building a feather isn't ether , you need balance. You think that by adding a coat of shellac on the inside will eliminate humidity issue? it won't shellac is hygroscopic and will take on water.
From an engineering stand point you are adding a small amount of weight but you also are locking the wood from breathing and allow the wood to find a natural balance of humidity. If this were such a good thing to do , there would be many more builders doing it , and what I am saying , is that there is NO real benifit from doing this , but if you thing it is the thing to do , do it . Your clientele will either accept it or not.
I am a trained luthier , I didn't teach myself but regardless of the ideology this is a moot point , those of you that think this a good , what training do you have and how many guitars have you built . You asked a question for which I gave an answer . You may not like my answer and that is fine , but not one of you have given are real credence to what the benefits are . You gave opinions but there are not facts .
Have any of you actually played one ? Have any of you worked on one ? How many of you built one ? This topic comes up often at symposiums and not many of the experienced builders use this technique . A few tried it and stopped as it didn't really do anything. The best thing is for those of you that believe it to be a good thing , build 2 guitars and do a blind study .
When working on a inside finish ,you make the repair more difficult , yes a little wash coat won't hurt but try and get a good glue joint but it is more difficult than if the wood was raw. I don't intend to upset anyone but to get some rational as to what the experience level is . Like I said ,if you think this is good , do it . I am telling you that from the experts that I speak to and from my own experience there is no advantage .

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John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

Certainly on classicals I've played, you deaden the sound if you hug the back. So the back is involved with more than shape.

I wonder if a light finish inside reduces dust adhesion, and maybe reduces the need for frequent interior cleaning?

Filippo Morelli got it right . I do understand the importance of the guitar and its weight . The top is the major contributor for tone. For the record I don't want to upset anyone , but I do understand the science behind the guitar . The back and sides do infer a bit on the guitar but it is the top and the air cavity that will do most of the work.
this is my last post on this subject . I agree that we are allowed to disagree , lets not get disagreeable . If anyone took any offense , that was not my intent , but in all forums when we are dealing with different theories and ideas we will at time not see things eye to eye . No true discovery was made by status quo thinking , and it is the dreamers that often make the discovery , still , not all ideas are good ideas .

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John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

Hi John - please don't take any offense if it seems as if anyone here is questioning you - questioning posts and information shared is the basic purpose of forums, discussion forums.

Personally I could care less if anyone uses shellac on the inside of their boxes. As stated previously I have not yet done this but I do see that there is some potential benefit in certain situations. For example one of my customers came over yesterday afternoon and his Heshtone went from 30ish RH in his house to 20ish RH outside where it sat in the back of a Ford Expedition while my client had a few... and then to the 45ish RH of my shop where we jammed and my client had a few more... I actually started wondering if it would be easier for this guy to use beer inside his Planet Waves humidifier.... But I digress....

I worry about guitars in this climate and even though I take great care to hammer the points of good RH management home to my clients people are going to be people and perhaps not use the cases with humidifiers, keep the guitar in the case, or use the Planet Wave humidifiers that I supply with my guitars. BTW as you mentioned keeping the guitar in the case in the winter is a great practice to do - highly recommended!

As far as engineering data to support that sealing the inside of the box has a benefit I would bounce the question back and ask for data that supports that sealing the inside of the box does not slow the potential harm of rapid RH changes.

I have played two guitars that were sealed on the inside with shellac and both guitars were 2 of the very best sounding guitars that I have ever played. Both were Somogyi's. I don't know John if Somogyi has built as many guitars as you, over 100 as you said and say frequently..., but I suspect that Somogyi is a competent builder.

Regarding mass being added by shellac and shellac being hygroscopic: My impression is that if one tested to determine how much mass is added by shellac they would find it to be, well... mouse nuts.... The alcohol in shellac will in time flash off and leave only the shellac in it's very thin layered form. The one entire guitar that I french polished had just under 2 ounces added to the entire guitar by the process of Z-Poxy pore filling and many, many coats of french polish. This leads me to believe that sealing the inside of a box with a coat or two of shellac is going to add grams and not ounces.... and again the weight of the alcohol will flash off. My impression is also that it is the alcohol that is water absorbent not the shellac or that shellac is minimally hygroscopic.

BTW I want to take this opportunity to wish everyone Happy Holidays!!!!!!

Bogdanovich does not seal the inside of the guitar, not in his book anyway. He shellaces (let's make it a verb…) the back braces and centre graft only, the back is left finely sanded or scraped, but raw. He does finish the inside of the sides, though.

I wonder if it's not more of a visual thing, like let's make the inside shinny, nice and tidy. I do not believe in the moisture exchange being slowed down by a washcoat on the inside.

I definitely do not shellac the inside of my guitars, and have no plan to. And I do not notice problems in keeping the guitars in tune in spite of the wide RH changes we have here in northern N-E. I keep my personal guitar in the house, outside of the case, wherever I fancy playing it, and do not pay attention about the RH, heat, cold or anything. Well, I do not keep it too close to the woodstove… It's meant to be played, it's a tool, and it seems to be doing just fine.

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Laurent Brondel
West Paris, Maine - USA
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