My 1975 Kohno Model 10 classical guitar and all of the other Kohno's I have seen have finish applied on the inside of the soundbox. I have heard that there are a few other luthiers who finish the inside. I am curious to know the reason Mr. Kohno finished the inside.
Mr. Kevin Hall, Canadian Luthier/Guitar Repairman posted on the Builders Newsgroup that "In the late 70s Yamaha built a number of very high-end classical guitars for Canadian classical 'star' Lionna Boyd. Some of those were varnished in and out, but Ms. Boyd disliked them to the point where she demanded that the firm pull the backs off and scrape out the finish within."
What are the advantages and disadvantages of finishing the insides?
I believe that Masaru Kohno, who died in December, 1998, was a very serious and capable luthier and I am sure he had good reasons for finishing the insides. I would just like to know what they were.
Finishing the inside is thought by it's practitioners to reduce the incidence of cracking due to humidity changes. I have not seen any proof of this, although, to be sure, it would a tough one to prove either way.
Usually any inside finish is quite thin, and that would minimize the useful effect. Any amount of finish is generally thought to be detrimental to the guitar's sound, particularly on the top, since it adds weight and (often) damping. Doubling the weight by finishing the inside would have to be worse for the sound if that's true.
Certainly any buildup of finish on the inside that sufficed to protect the wood would make later repairs difficult. Glue does not stick well to finished surfaces, and it would be difficult to scrape away finish if one wanted to put studs across a crack. For that reason alone I'd rate it as a bad idea.
> Finishing the inside is thought by it's practitioners to reduce the > incidence of cracking due to humidity changes. I have not seen any > proof of this, although, to be sure, it would a tough one to prove > either way.
> Usually any inside finish is quite thin, and that would minimize the > useful effect. Any amount of finish is generally thought to be > detrimental to the guitar's sound, particularly on the top, since it > adds weight and (often) damping. Doubling the weight by finishing the > inside would have to be worse for the sound if that's true.
> Certainly any buildup of finish on the inside that sufficed to protect > the wood would make later repairs difficult. Glue does not stick well > to finished surfaces, and it would be difficult to scrape away finish > if one wanted to put studs across a crack. For that reason alone I'd > rate it as a bad idea.
> Alan Carruth / Luthier
Then there's the old woodworkers' point of view that what ever you do to one side of a wooden panel should be done to the other side in order to minimize warping, cracking etc.
I've also heard the argument that finishing the inside creates a more reflective surface to reduce any damping effect of raw wood. Just goes to show that for every theory there may well be an equal and opposite theory. ;-)
Obviously from a repairmans' standpoint the last thing we want is finish inside as well as out to make future repairs more difficult. I'd rather rely on well seasoned wood and careful assembly at a controlled relative humidity level to keep things stable as opposed to hoping another layer of finish will keep moisture in and out, but several excellent luthiers do finish the interior for reasons of their own.
alcarruth <alcarr...@aol.com> wrote: > Finishing the inside is thought by it's practitioners to reduce the > incidence of cracking due to humidity changes. I have not seen any > proof of this, although, to be sure, it would a tough one to prove > either way.
> Usually any inside finish is quite thin, and that would minimize the > useful effect. Any amount of finish is generally thought to be > detrimental to the guitar's sound, particularly on the top, since it > adds weight and (often) damping. Doubling the weight by finishing the > inside would have to be worse for the sound if that's true.
> Certainly any buildup of finish on the inside that sufficed to protect > the wood would make later repairs difficult. Glue does not stick well > to finished surfaces, and it would be difficult to scrape away finish > if one wanted to put studs across a crack. For that reason alone I'd > rate it as a bad idea.
> Alan Carruth / Luthier
Although it doesn't sound good, I've heard that some guitar manufacturers finish the entire soundoard before gluing on the bridge. So, I wonder if cleats couldn't effectively be glued to a finished soundbox interior.
>> Finishing the inside is thought by it's practitioners to reduce the >> incidence of cracking due to humidity changes. I have not seen any >> proof of this, although, to be sure, it would a tough one to prove >> either way.
>> Usually any inside finish is quite thin, and that would minimize the >> useful effect. Any amount of finish is generally thought to be >> detrimental to the guitar's sound, particularly on the top, since it >> adds weight and (often) damping. Doubling the weight by finishing the >> inside would have to be worse for the sound if that's true.
>> Certainly any buildup of finish on the inside that sufficed to protect >> the wood would make later repairs difficult. Glue does not stick well >> to finished surfaces, and it would be difficult to scrape away finish >> if one wanted to put studs across a crack. For that reason alone I'd >> rate it as a bad idea.
>> Alan Carruth / Luthier
> Although it doesn't sound good, I've heard that some guitar manufacturers > finish the entire soundoard before gluing on the bridge. So, I wonder if > cleats couldn't effectively be glued to a finished soundbox interior.
> Regards, > John E. Golden
I know Titebond sticks well to Shellac. I would expect HHG to also. But I haven't tried it.
I've tried it and the bridge popped off when the customer put higher tension string on the guitar. As I recall, this was using the LMI white glue. On the positive side, it came off fairly cleanly with only a small amount of tear out which was easily repaired. A simple repair, but one I'd rather not have to do.
I used to scrape all the finish off the bridge area for every guitar, but now I use masking tape and only scrape/sand it minimally to assure good wood to wood contact.
> > Although it doesn't sound good, I've heard that some guitar manufacturers > > finish the entire soundoard before gluing on the bridge. So, I wonder if > > cleats couldn't effectively be glued to a finished soundbox interior. > te > > Regards, > > John E. Golden
> I know Titebond sticks well to Shellac. I would expect HHG to also. But I > haven't tried it.
Manufacturers who slap bridges down on the finish generally do so using a cyanoacrylate adhesive ( Super Glue). They're relying on the adhesion of their finish ( usually UV cured poly) to hold things together, and it's a crappy idea. When such joints let go they often bring sections of the finish with them, turning a normally simple bridge re-glue into a major touchup headache.
>> Finishing the inside is thought by it's practitioners to reduce the >> incidence of cracking due to humidity changes. I have not seen any >> proof of this, although, to be sure, it would a tough one to prove >> either way.
>> Usually any inside finish is quite thin, and that would minimize the >> useful effect. Any amount of finish is generally thought to be >> detrimental to the guitar's sound, particularly on the top, since it >> adds weight and (often) damping. Doubling the weight by finishing the >> inside would have to be worse for the sound if that's true.
>> Certainly any buildup of finish on the inside that sufficed to protect >> the wood would make later repairs difficult. Glue does not stick well >> to finished surfaces, and it would be difficult to scrape away finish >> if one wanted to put studs across a crack. For that reason alone I'd >> rate it as a bad idea.
>> Alan Carruth / Luthier
> Although it doesn't sound good, I've heard that some guitar manufacturers > finish the entire soundoard before gluing on the bridge. So, I wonder if > cleats couldn't effectively be glued to a finished soundbox interior.
On Sun, 14 Aug 2011 16:26:44 -0700 (PDT), alcarruth
<alcarr...@aol.com> wrote:
>Finishing the inside is thought by it's practitioners to reduce the
>incidence of cracking due to humidity changes. I have not seen any
>proof of this, although, to be sure, it would a tough one to prove
>either way.
I did that to one of my instruments for exactly this reason. Many,
many years ago, I had a custom order from a musician who lived in
Brunei and we decided that the instrument was more likely to survive
the extremes in temperature and humidity and potential infestations if
it were completely sealed.
>Usually any inside finish is quite thin, and that would minimize the
>useful effect. Any amount of finish is generally thought to be
>detrimental to the guitar's sound, particularly on the top, since it
>adds weight and (often) damping. Doubling the weight by finishing the
>inside would have to be worse for the sound if that's true.
This wasn't thin, this was thorough. Unfortunately (1) this instrument
was non-standard in a lot of ways (he was a tiny, thin man with tiny
hands and the instrument was built to suit him) so it was hard to tell
what the effects were. Unfortunately (2) I never heard from him again
after he went back to Brunei so I have no data on what happened to the
instrument or whether it is still being played
>Certainly any buildup of finish on the inside that sufficed to protect
>the wood would make later repairs difficult. Glue does not stick well
>to finished surfaces, and it would be difficult to scrape away finish
>if one wanted to put studs across a crack. For that reason alone I'd
>rate it as a bad idea.
The Catch 22 as I see it is that if the sealing works, you shouldn't
have cracks and splits in need of repair.
This has been a fairly pointless contribution to the thread but it
seemed like a good way of letting you know that my recent silence is
not because I'm lying dead and undiscovered on my workshop floor - or
worse that I've abandoned USENET for Facebook - but because I've been
away from the UK visiting one of Her Majesty's former penal colonies
in the southern hemisphere.
On Aug 23, 8:10 pm, "Kevin Hall" <timberl...@webhart.net> wrote:
> Manufacturers who slap bridges down on the finish generally do so using a > cyanoacrylate adhesive ( Super Glue). They're relying on the adhesion of > their finish ( usually UV cured poly) to hold things together, and it's a > crappy idea. When such joints let go they often bring sections of the > finish with them, turning a normally simple bridge re-glue into a major > touchup headache.
CA is the most useful stuff since duct tape, but isn't it brittle and liable to fail under a sharp impact?
> Manufacturers who slap bridges down on the finish generally do so using a
> cyanoacrylate adhesive ( Super Glue). They're relying on the adhesion of
> their finish ( usually UV cured poly) to hold things together, and it's a
> crappy idea. When such joints let go they often bring sections of the
> finish with them, turning a normally simple bridge re-glue into a major
> touchup headache.
CA is the most useful stuff since duct tape, but isn't it brittle
and liable to fail under a sharp impact?
++++++++++
Yes. And sometimes that is used for temporary assy situations. But it can be pretty strong too. The problem is that with wood, it soaks in (unless thickened) leaving a dry joint. It also attacks some finishes (all finishes?).
I've used it as a filler for both spray can and catalysed poly, and it will make a completely seamless bond, at least where I have used it. I repaired some small dings in my Martin D-16 top (polished catalysed poly) with it, and literally couldn't find them after a few weeks when the grain had come back up again after sanding.
Almost OT - Differences in hardness between the finish and the repair can be an issue, so I remove as much of the filler as possible before sanding. I use a very sharp 1" chisel, with a bit of masking tape at over the edge at each end so that the centre of the blade is just above the working surface. I've also used a Stanley knife blade with tape at each end as a scraper, you can bend it by pushing in the middle of it with your thumbs to get it lower if need be.
> It also attacks some finishes (all
> finishes?).
> Dave
> ***************
> I've used it as a filler for both spray can and catalysed poly, and it > will make a completely seamless bond, at least where I have used it. I > repaired some small dings in my Martin D-16 top (polished catalysed poly) > with it, and literally couldn't find them after a few weeks when the grain > had come back up again after sanding.
> Almost OT - Differences in hardness between the finish and the repair can > be an issue, so I remove as much of the filler as possible before sanding. > I use a very sharp 1" chisel, with a bit of masking tape at over the edge > at each end so that the centre of the blade is just above the working > surface. I've also used a Stanley knife blade with tape at each end as a > scraper, you can bend it by pushing in the middle of it with your thumbs > to get it lower if need be.
