Humidity and back bow

[Photojeep]

Just this past Thursday night, I inadvertently left my Martin DCPA4 Siris out all night sitting on a guitar stand. Normally, however long I play/practice during the day, I always put that guitar back into its case so it's properly protected and humidified over night. It is not uncommon for my guitars to sit in their cases for several days at a time as I'm playing a different one.

Anyway, when I woke up Friday morning, and as I walked past my office/guitar room I saw the guitar still sitting on the stand. I gave her a quick strum with my thumb as she sat there and didn't see or hear anything amiss so I just left her out so I could play more without when I got the urge.

All was fine until later that day I placed a capo on the first fret to practice some of the music I play at my church and ran into some strange sounds when picking single notes for a different song. My first thought was my hand was tired or slightly out of position and I wasn't fretting cleanly, but upon closer inspection found the neck no longer had the slight up-bow she normally has and had developed a very slight back bow.

Once I realized what had happened I immediately put her back into the case with all the humidipaks in place and closed it up. All told, the guitar was out on the stand for a little over 24 hours.

I live in Las Vegas so we have very little, if any, humidity during the summer and of course run air conditioning 24 hours a day which dries out the inside air quite a bit. Currently our house humidity is around 18% (outdoors it can go down to single digits during the summer months)

I know many of you have whole-house or room humidification, something I do not have nor have really had any need for. I rely on the humidipak system of case-humidification. I have been, and still am, very satisfied with the paks.
I've lived almost 40 years here and have become accustomed to the dryness and really don't find it personally uncomfortable. Yes, we drink a LOT of water so maybe that helps.

This afternoon, Sunday, I checked her and the neck was much straighter and a slight truss rod adjustment brought it back where it belongs so there seems to be no long term issues.

My question is this:

Is it "normal" for a neck to develop a back bow (as opposed to an up bow) as it begins to dry out? I have no knowledge of what wood will do in very dry or very wet conditions so I'm curious. By the way, there were no fret ends beginning to "sprout" or any other symptoms of a dry guitar neck.

I was very surprised to have it happen in so short a time and the only thing I can imagine is that it was closer to this to begin with and then dried out enough to beginning bowing backwards.

Any way, I'm very interested to hear from those of you with more experience in these matters.

Thank you in advance,
PJ

[Brucebubs]

I'll be interested to read opinions on this thread.

I thought it was the thinner soundboard tops that would be more likely to react to humidity changes than a much thicker neck .. with truss rod?

Don't over humidified (wet) tops swell & belly and action goes high and under humidified (dry) tops shrink & dip and action goes low & buzzy?

[zhunter]

In general

Dry = more relief
Wet = less relief

hunter

[Photojeep]

Originally Posted by zhunter

In general

Dry = more relief
Wet = less relief

hunter

So if I'm understanding the terms above correctly, I just recently experienced the opposite.

Hmmm
PJ

[Russ C]

Originally Posted by zhunter

In general

Dry = more relief
Wet = less relief

hunter

That makes sense to me as an unsealed fretboard could absorb more moisture than the neck and swell to cause a back bow .. whether that happens along the grain is another thing - some timbers only swell laterally I think.
Where I live (Melbourne) the humidity doesn't vary all that much so I can't comment from much experience - I've just tweaked things as needed and never dwelt on why.

[Russ C]

Originally Posted by Photojeep

So if I'm understanding the terms above correctly, I just recently experienced the opposite.

Hmmm
PJ

And it's hard to ignore that isn't it. I look forward to learning about this.

[JayBee1404]

I find it hard to believe that one day out of its case affected the neck-relief and, as pointed out by zhunter, a dry neck tends to have increased relief, not less relief.

I think it’s far more likely that the top had sunk a little - possibly over a prolonged period - which caused the low action.

A few questions:-

1) You say that, “upon closer inspection” you found that, “the neck no longer had the slight up-bow she normally has, and had developed a very slight back-bow”. How did you determine this? By a straight-edge along the frets, by the ‘E-string depressed at the 1st and 14th fret” method, by sighting down the board, some other method?

2) Did you slack the strings off when checking the neck?

3) Have you noticed the fret-ends feeling ‘sharp’ recently? This is often an early sign, along with a sinking soundboard, of a dry guitar.

4) Did you check the soundboard-belly, by laying a straight-edge across the bottom bout directly behind the bridge, and noting the gap at edges of the guitar? If so, do you recall what the measurements were?

5) Is there a humidifier in the case permanently, or did you only put the Humidipaks in when you noticed the apparent problem with the guitar?

6) If you do keep the Humidipaks in there permanently, do you have an in-case hygrometer and monitor the RH in the case regularly? If ‘yes’, what would you say is the average RH reading in the case?

Apologies for the Spanish Inquisition (“Nobody expects the Spanish Inquisition!” ), but your story has me intrigued, and I’m just trying to flesh out the bones a little.

[Photojeep]

Originally Posted by JayBee1404

I find it hard to believe that one day out of its case affected the neck-relief and, as pointed out by zhunter, a dry neck tends to have increased relief, not less relief.

I think it’s far more likely that the top had sunk a little - possibly over a prolonged period - which caused the low action.

A few questions:-

1) You say that, “upon closer inspection” you found that, “the neck no longer had the slight up-bow she normally has, and had developed a very slight back-bow”. How did you determine this? By a straight-edge along the frets, by the ‘E-string depressed at the 1st and 14th fret” method, by sighting down the board, some other method?

2) Did you slack the strings off when checking the neck?

3) Have you noticed the fret-ends feeling ‘sharp’ recently? This is often an early sign, along with a sinking soundboard, of a dry guitar.

4) Did you check the soundboard-belly, by laying a straight-edge across the bottom bout directly behind the bridge, and noting the gap at edges of the guitar? If so, do you recall what the measurements were?

5) Is there a humidifier in the case permanently, or did you only put the Humidipaks in when you noticed the apparent problem with the guitar?

6) If you do keep the Humidipaks in there permanently, do you have an in-case hygrometer and monitor the RH in the case regularly? If ‘yes’, what would you say is the average RH reading in the case?

Apologies for the Spanish Inquisition (“Nobody expects the Spanish Inquisition!” ), but your story has me intrigued, and I’m just trying to flesh out the bones a little.

No worries about the inquisition! Here goes:
1) I determined this by sighting down the neck (from both ends) and using the strings as a straight edge. Doing so showed the neck had bowed backwards. And of course, when fretting a string at the first fret the string was in direct contact with the second fret.

2) Nope, see #1 above.

3) No fret sprout anywhere along the neck (I mentioned this in my original post.)

4) I did not check the body for any bellying or anything else so I'll have to check that out.

5) I have used the Humidipaks continuously for years. I always have paks in the case and replace them when they get crunchy.

6) I have Oasis hygrometers in all my guitar cases and even used the "calibration" from Boveda to determine if they were giving me accurate readings. As a result of doing this procedure, I have written if I should add or subtract from the reading on the hygrometer. This particular guitar/case combination has consistently been between 38 and 43% RH for the past 2 years.

One thing I failed to mention in my earlier post is that the fretboard on this guitar is Richlite. I don't know if that would make a difference but wanted to clear up my omission.

Best,
PJ

[jseth]

Yep... with either my Angus 6 or 12 string, or my Goodall Grand Concert, the results are the similar...

High humidity = increased forward set, varying depending upon "how high the rh%" is and how long it stays there...

Low humidity = backset with all three, although I will say that my Angus 12 string (1983) has possibly the most stable top/neck of ANY guitar I've played; she's a little overbuilt (Mark Angus' first and only 12 string after all...), but that neck just want s to stay perfect. Takes long time for that one to move at all.

If your guitar was already even close to borderline rh%? A full day would do that in a hurry... no need to adjust it; I'd bet with a little moisture added back, the neck will come right back.

Tough to manage humidity and acoustic guitars in the desert...

[Photojeep]

...Tough to manage humidity and acoustic guitars in the desert...

Tell me about it!

And yes, it is entirely possible the guitar was close to dead flat before my "incident"

Best,
PJ

[CaptRedbeard]

Like others, I am curious why one day out of the case would have such a dramatic effect. I live in the high desert of Northern Nevada and today the humidity was 11% outside the last time I checked. I keep the house humidity, using a large size unit, at between 35 and 40% and have never had that happen to me when I leave a guitar out overnight. If you over-humidify your instruments then an abrupt change may cause a problem. Put a small humidity reader in your guitar case when you put one of those individual sponge units in the case. Check the next morning and read what the humidity is. Would be interested to read what the results are.

[cleveguitar]

in my experience, very dried out guitars will have a sunken top and probably a big hump in the fretboard extension. This will cause major buzzing issues and pretty quick too, idk about overnight though. After the top is collapsed like that, I haven't found a very good way to repair it other than a partial refret and just adjusting the whole set-up to the new shape of the guitar. If you play your guitar a lot and you are in Las Vegas in mid August then your guitar is as dry as a toothpick, case humidifier or not.

[Photojeep]

...and you are in Las Vegas in mid August then your guitar is as dry as a toothpick, case humidifier or not.

So where in Las Vegas do you live? And when have you seen/played my guitars that you know so much about them? Surely I would have seen you in my house. I know I’m getting up there in years but I’m certain I would have noticed you...

I appreciate you contributing to the thread but not your characterization of the condition of my guitars.

Respectfully,
PJ

[AndrewG]

Originally Posted by cleveguitar

in my experience, very dried out guitars will have a sunken top and probably a big hump in the fretboard extension. This will cause major buzzing issues and pretty quick too, idk about overnight though. After the top is collapsed like that, I haven't found a very good way to repair it other than a partial refret and just adjusting the whole set-up to the new shape of the guitar. If you play your guitar a lot and you are in Las Vegas in mid August then your guitar is as dry as a toothpick, case humidifier or not.

Yes, this was the case with a very dry CEO-5 I bought, slightly used. A noticeable dip in front of the bridge was cured by leaving a small bowl of water next to the guitar, sitting on a stand. A week or so later and the top popped right back up. The thin tone also became much more robust with increased humidity. The neck was stable though and there was no fret sprout.