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PostPosted: Sat May 28, 2016 8:56 am 
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Joined: Sun Mar 09, 2014 8:13 pm
Posts: 1309
I'm going to post this in a couple of sections of the forum, because it illustrates the importance of humidity control.

We often talk about the lack of humidity which results in the wood drying out, causing damage, but we rarely talk about what happens when there is TOO MUCH humidity.

This custom OM-45, comes from southern Georgia, where there is a lot of humidity year around. Forced heat and air conditioning, act as dehumidification, but in this area, neither is used much, except for the dog days of August. This guitar was kept in ~ 77% RH in a residence. The owner sent the guitar to me. Since it's under warranty, I brought the guitar to John Hall, since he is certified for Martin Warranty repair.

The guitar had a very high action and the binding had started coming off in a couple of areas. When a ruler was placed over the area below the bridge, it was obvious that the guitar was very swollen from excessive humidity, causing the neck relief to change and popping the binding off. We're lucky we caught it; guitars can eventually come completely apart when the wood swells to this extent. The owner said that the guitar never sounded very good. He even had Martin replace the entire top with a nice Adi.

He placed the guitar in his basement to "dry out". The next day, the difference was startling. The belly bulge had decreased substantially and the neck started to straighten out. The binding will be reglued after the guitar completely dries out, which takes about two weeks.

I discussed the problem with the owner and found that he was having trouble with most of his guitars. He has since gotten a good dehumidifier for his guitar room. He told me that his guitars were much happier.

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PostPosted: Sat May 28, 2016 10:22 am 
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Joined: Fri Mar 03, 2006 7:09 pm
Posts: 5419
Location: Hegins, Pa
very good point Dianne.
RH control in building and storing guitars if often not though of until it is too late. I have a serious investment in guitars. I have a climate controlled area. I have a humidifier set to turn on at 40% and a dehumidifier set at 50%.

Let me help you understand what happens.

In uncontrolled climates the RH can rise and fall often in high amounts in a short period of time. While it seems to be catastrophic a few hours or even a few days won't harm the instrument but may make it noticeably different. Once the RH returns to normal all is fine.
the older the guitar often the more stable, the issues arise from the top and back plates being held by cross grained braces. As the top expands and contracts it will push and pull against the braces making them rise and fall. When allowed to remain in the extremes for long periods of time the plates will change and the braces will slip or loosen. Sometimes the tops especially will contact to the point that they pull themselves apart and form a crack.
Too dry the tops sink and the plates go into tension and this is what pulls them apart.
too high the tops expand , and since the bindings are set to a specific length , the circumference of the shape changes. This will pull bindings off the body or separate at the joints.
A little care will solve so many issues.
WARNING SIGNS OF DRY
fret ends appear sharp
as the fretboard shrinks the fret ends become exposed and you notice them

Grain becomes more pronounced
you will notice the top grain more corduroy like.

Top will start to sink and action will become lower. Buzzing may also appear.

a crack on the top often at the fret board extension will often form from the difference of woods contraction. Ebony will not move as much as sitka and the crack often forms along the side.


TOO MUCH HUMIDITY
top will belly and action rises.

Again the top may crack along the fretboard extension from the differences in the woods expansion properties

binding glue joints will become visible as a finish sink.

A noticeable change in the guitars tone

these are just a few of the issues

_________________
John Hall
Blues Creek Guitars Inc
Authorized CF Martin Repair Center
Board of Directors of Association of Stringed Instrument Artisans
http://www.bluescreekguitars.com


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PostPosted: Sat May 28, 2016 11:47 am 
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Joined: Wed Nov 26, 2014 7:52 pm
Posts: 296
Location: Saint Paul, MN
Excellent info. Thanks for sharing that.

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Learning every day.


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