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How much are carved topped arch tops affected by humidity (or lack thereof). I am very aware of the effects of humidity on flat topped acoustics, I see quite a few during the winter with flat tops and even cracked tops. One of the first things I do when a flat top hits my bench is to lay a straightedge across the top behind the bridge and look to see how much of a dome I have. If there isn't what I expect as normal I put the guitar away with a hydration system to try to bring it back.
But I can't use that test on a carved archtop since I don't know how much arching the builder built in to it. I have a lovely little Anderson right now that has low action and buzzy all over the fretboard. Rather than just crank the action up until it stops I'm wondering if I should force some moisture into it first (I currently have a very nice HD28 is the shop with a big damp sponge in a baggie inside the sound box, should I do the same with the Anderson?) And since someone will ask, the Anderson currently has 0.005 inch of relief, twelfth fret action is between 40 and 60 thousands, and very slight fret sprout which I will dress after its become stable. The finish is kind of wavy following the grain on the top.
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03-19-2026 02:05 PM
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why not just keep it at the correct humidity for a few weeks and go from there?
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This kind of a surprising question-if you're running a guitar shop or any shop dealing w wood you should be keeping the humidity around 40-50 % no matter what kind of guitar you're working on, this is sop. Archtops are prone to cracking in low humidity just like flattops and if you have a solid body you want to prevent fret sprout.
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Thank you all for your advice, I think there is a miss understanding. I am an amateur builder and I do a few repairs. I am very cognizant of the effects of low humidity, I keep my shop and my wood storage and my music room 40 or 45 percent year around. I keep my guitars in cases with humidifiers. Local musicians bring guitars to me for setups and some work.
I know the symptoms of a dry ("flat top") guitar (flat or sunken top, sharp frets, wonky finishing, low action). I see that a lot, tell the owner that I can't do anything until the guitar is back stable with respect to humidity. I fix the occasional cracked top. I know how to do this stuff.
My question was very simple, are carved archtops as sensitive as a "flat top" to humidity swings? I had one brought to me yesterday with very low action and the other symptoms, rather than just screw the bridge up until it stopped buzzing I sent the owner away with a couple of sponge/baggie humidifiers and told him to com back in a month.
I assume a carved archtop would be sensitive, I wanted to confirm that. I know how to test a Martin for proper hydration, how do I test a carved top? He may bring the guitar back tomorrow, I want to know what to look for.
Thank you
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since you typically can't put a hygrometer in an archtop like you would a flattop you can put it in the case w/the lid closed, behind the headstock or under the neck if there's room
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Originally Posted by wintermoon
Actually I plan to put a couple of those sponge-snake things that were popular some years back, one in each f-hole. Then a standard sponge-baggie in the headstock compartment and let it set for a few weeks. I'm going to raise the action in the meantime to make it playable and lower it back when/if it comes back to normal. And give the owner a little lecture
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if it's thicker than a flattop, like an archtop's top and back typically is it might be slightly less prone to developing cracks, though the sides of both would be about the same. but wood is wood, you don't want to tempt fate. Originally Posted by Freeman Keller
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Repaired by Gibson under warranty.
Danny W.
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I've only owned laminated-top archtops and can't speak to carved vs flat tops' relative susceptibility to cracking. But my experience has been that archtops that have fingerboard extensions extended above the top (as opposed to the way flattop fingerboards are glued to the top) can have bigger changes in action and relief than flattops as temperature and humidity changes. An in-case humidifier and/or regularly adjusting relief and bridge height come with the territory. Originally Posted by Freeman Keller
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Also, despite the fact that some people are comfortable putting wet things in their guitars like you suggest here...
"Actually I plan to put a couple of those sponge-snake things that were popular some years back, one in each f-hole."
I would never put something wet in any guitar I own, sponge, humidifier, etc. I realize that not everyone has a place that they can control the humidity, but these types of things I don't trust.
Like I said, some do.
I have a small room that I can control with a room humidifier that is very effective.
Only once did I try an in-case device. It was a bad decision, which I still regret.
That's my story.
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It depends on how the top is carved and braced. I have found my archtops to be similar to my acoustics with humidity. Action and sound change if humidity changes too much. Took me a few years to get organized, but thankfully there are no extremes where i live so no damage occured. Now i keep everything in cases/bags in a humidity controlled room.
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As a fellow repairman(full time), I am frequently presented with customer's instruments(during the winter heating season here in the NE) that show various degrees of dryness, or lack of proper humidification. I immediately ask the owner if they have been properly humidifying the instrument: invariably, one way or another, they have not. After many years, it's become a slight annoyance: how many times do I have to tell owners to properly humidify their instruments?!
IME, solid wood archtops respond to humidity like flattops, and show similar changes. Low action, high bridges, buzzing...and fret sprout. If there is fret sprout on an older guitar, during the winter, it's from lack of humidification.
When I get a seriously dried instrument in for repair, I first put it into a 'hydration chamber': a framework box, covered in plastic, in which I hang the guitar, with a pan of warm water at the bottom. Over the course of a week(or however long it takes), the instrument resumes most(not always all) of its previous setup and dimensions. After that, I make any needed repairs.
It's happened repeatedly this winter!
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That almost looks like a split in the center seam, where the two halves are glued together. Originally Posted by Danny W.
Repaired by Gibson under warranty.
Danny W.
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I have become born-again about proper humidification, after suffering one catastrophe, and some near misses. I have a good-sized room that serves as my "guitar humidor" where the room itself is kept in the mid-to-high forties, and each guitar is kept humid in its case, with hygrometer, etc. I find the higher-end composite cases (Calton, Hoffee) are easy to keep regulated.
I worry much less about plate cracking than I do about the effect of humidification on the neck. Here in Colorado, necks try mightily to backbow. Once you run out of lefty-loosy, you're in serious trouble. When evaluating an instrument, that is by far my biggest concern. For example, I had to pass on a very high-end DAQ with a completely loose trussrod. The neck was straight, albeit with no relief to speak of, and played fine--but I knew that if I brought it from NYC to Colorado, it would be like living with a time-bomb.
So for awhile now, all my guitars, flat-top and archtop, are dialed-in, and optimized. The price of properly humidified, healthy guitars is eternal vigilance!
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I had that experience w/ an L-7, and my luthier's explanation began with : " You're out of threads. "........So yes, the tr can be operable, but even so, won't correct every issue the guitar may have. And this luthier's most oft-used first step was placing the instruments in his basement for a good week, and letting them re-hydrate. Then he'd get at the repairs they'd need. Originally Posted by Rico59
I have become born-again about proper humidification, after suffering one catastrophe, and some near misses. I have a good-sized room that serves as my "guitar humidor" where the room itself is kept in the mid-to-high forties, and each guitar is kept humid in its case, with hygrometer, etc. I find the higher-end composite cases (Calton, Hoffee) are easy to keep regulated.
I worry much less about plate cracking than I do about the effect of humidification on the neck. Here in Colorado, necks try mightily to backbow.
Once you run out of lefty-loosy, you're in serious trouble.
When evaluating an instrument, that is by far my biggest concern. For example, I had to pass on a very high-end DAQ with a completely loose trussrod. The neck was straight, albeit with no relief to speak of, and played fine--but I knew that if I brought it from NYC to Colorado, it would be like living with a time-bomb.
So for awhile now, all my guitars, flat-top and archtop, are dialed-in, and optimized. The price of properly humidified, healthy guitars is eternal vigilance!
I agree -- made a hydration believer out of me.
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