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#1
07-19-2015, 08:58 AM
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On applying finish inside an acoustic guitar
Have always wondered what affect there would be if a finish was applied to the inside as part of a new build---not for aesthetics, but only to seal the interior wood. This would be in an effort mainly to reduce movement by absorption and evaporation of moisture. How would it affect the structure, the longevity, and the voice of the instrument. Am especially interested in substantiated opinions but conjecture is welcome. Thanks for your responses.
Skip (@ sealevel) 
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#2
07-19-2015, 03:16 PM
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It is rarely done, but sometimes discussed. Perhaps the best reason I can see as to avoid it is it would make future crack repairs (cleating) more problematic.
That said, it probably will slow the transfer of humidity into and out of the wood, but whether this is an advantage or not is likely debatable and also dependent upon a guitar owner's usage of his guitar. If you are taking it into a steam sauna for 15 minutes at a time, sure, finish on the inside is likely a good thing... But any humidity that gets INTO the wood will take longer to get OUT as well... That said, some classical guitar makers include this feature. Can't name any off my head, but I know I've seen hand made classical guitars finished on the inside (sides & back - don't know about the top).
__________________
---- Ned Milburn NSDCC Master Artisan Dartmouth, Nova Scotia
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#3
07-19-2015, 04:44 PM
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Hello all. First post here, but I have been building archtop guitars and mandolins since 1999. Many archtop guitars are sealed on the inside as it is recommended by Bob Benedetto in his fine book on archtop guitar construction. I have always sealed the inside of my archtops and my mandolins with shellac and I have had no problems. The reason for sealing is given as helping to prevent the sudden loss of moisture during climate change.
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#4
07-19-2015, 04:46 PM
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Quote:
__________________
---- Ned Milburn NSDCC Master Artisan Dartmouth, Nova Scotia
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#5
07-19-2015, 05:13 PM
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You're right. I was going on memory. The actual quote from the book is, "The sealer is needed to help prevent the sudden absorption or loss of moisture during climate change. If the top or back plates absorb too much moisture the wood may swell and buckle. The more hazardous condition is sudden loss of moisture which may cause the wood to shrink and possibly crack."
Matt
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#6
07-19-2015, 07:03 PM
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I think Tim McKnight seals the inside of his guitars. As said, repairs might be an issue further on but the other school of thought says you would need less repairs. I guess if you were to coat it with anything shellac would be the easiest to remove if you needed to do any repairs.
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#7
07-20-2015, 11:14 PM
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Quote:
"Lastly the top (interior surface) is sealed with a thin wash coat of shellac. This adds stiffness and also retards the exchange of moisture from the wood. This allows the guitar to handle humidity changes in a more even and controlled manner." Source: http://www.mcknightguitars.com/process.html Man, I love Mcknight's transparency when it comes to his own build methods and philosophies. EDIT: Also, I just read through this thread and it had some good info (but maybe you already read this one?). Anyways, here it is: http://www.acousticguitarforum.com/f...d.php?t=202066 Last edited by Sam VanLaningham; 07-20-2015 at 11:24 PM.
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#8
07-22-2015, 11:00 AM
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regarding repairs and shellac, how hard can this really be?. a catastrophic failure of an order of magnitude? a critical disaster? it's just shellac. dissolve/remove it off the repair area and move on -and use better glue.
i would not worry about repair problems with a interior brushed in a wash coat of shellac or glair. if you're doing proper wiring of your cleats it is the least of your concerns. if you're repairing kerfing or bracing, you're clamping. now if a builder is applying a thick coat of poly or lacquer to the inside.. they know their punishment. Last edited by arie; 07-22-2015 at 11:13 AM.
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