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Old 01-25-2021, 01:26 PM
raybklyn raybklyn is offline
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Default Bridge and Belly Starting to Lift / Rotate ...Soundhole sinking

From what I have read and heard these are symptoms of lack of hydration at some time in guitar's lifespan.

The guitar I am speaking of has a saddle that has been filed down to compensate so the action / intonation is 100% spot on. So the problem is not impacting play today.

The longer term prognosis from local luthier is neck reset is imminent. Short term they recommend taking the strings off of tension and hydrating to try and cure the belly bulge and soundhole drop.

Does this make sense to everyone? I am a new owner of quality guitars so when one needs some TLC means I would like to confirm plan of action from several sources.


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Old 01-25-2021, 01:52 PM
PaulVA PaulVA is offline
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Usually over-dryness results in the top flattening both in front of the bridge toward the soundhole and also behind the bridge, it does not normally cause belly bulge behind the bridge. Making sure the guitar is properly humidified is a good next step, and if it hasn't been done already, I'd have your luthier check inside for a possible cracked top brace, that is another reason the top can deform.
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Old 01-25-2021, 01:54 PM
SkipII SkipII is offline
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Default Symotoms of humidity variances

A dry guitar—generally—will have:
- a caved-in area on the top between the fretboard end and the saddle;
- the bridge will appear rolled forward, lowering the action;
- sometimes a hump where the fretboard meets the guitar body;
- visible grain of the wood where the finish is sinking, or even micro-cracks at seams; and
- fret ends protruding from the side of the fretboard.

An over-humidified guitar will have a pronounced swell on the belly behind the bridge.

It is not typical to have the caved-top/rolled bridge condition and a swelled lower bout. If so, the failure may be in the bracing itself.

Yes, a good first step is to get the humidity stable (several days at least) and then see what the condition is.
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Last edited by SkipII; 01-25-2021 at 01:59 PM.
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Old 01-25-2021, 02:00 PM
warfrat73 warfrat73 is offline
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Belly bulge is generally a symptom of over-hydration, rather than under-hydration.

Though some deflection, and even fairly pronounced bellies are not terribly uncommon even on otherwise well hydrated guitars.

You can have a belly on a guitar because of normal deflection/typically bellying but have the guitar also be dehydrated.
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Old 01-25-2021, 02:06 PM
charles Tauber charles Tauber is offline
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Originally Posted by raybklyn View Post
From what I have read and heard these are symptoms of lack of hydration at some time in guitar's lifespan.
They aren't.

Prolonged forces by strings on a wooden structure causes the wood to permanently deform, a process known as cold creep. On a guitar, the area between the bridge and sound hole sinks and the area between the bridge and butt rise, creating an "S" curve from butt to sound hole.

The string forces attempt to "fold the guitar in half" causing the upper bout to rotate "into the sound hole": this causes the change in geometry that is compensated for by having a neck reset.

A completely different phenomenon is that wood expands and contracts as it absorbs and desorbs moisture in response to changes in its environment. With fixed edges, as a guitar top expands in width, it bulges/domes to accommodate the increase in size. (Most guitars are made with some arch already in the top: higher humidity increases that arch.) As the guitar top shrinks, it flattens, reducing any arch/dome that is in the top.

As the top expands and contracts, it takes the bridge with it, raising and lowering the string height. Generally, changes in geometry caused by changes in humidity are not permanent and will continue to respond to changes in humidity.

Don't randomly humidify or dehumidify a guitar. Instead, obtain an inexpensive hygrometer to measure the actual relative humidity of the immediate environment in which your guitar resides. Ideal relative humidity is in the 40 to 50% range. Once you know what the actual relative humidity is, you can then humidify or dehumidify as necessary.

Last edited by charles Tauber; 01-25-2021 at 02:22 PM.
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Old 01-25-2021, 02:24 PM
Wild Bill Jones Wild Bill Jones is offline
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Many years ago my Rockbridge had all the same symptoms you describe. Randall and Brian at Rockbridge explained my guitar was very dry (in humid NJ...go figure). They humidified it for a month in a plastic bag and all was well again. I have carefully kept the humidity under observation and control on all my instruments ever since. Hope this helps.
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