I've been rebuilding an old Favilla F5. I pulled the top. Cleaned out several bad crack repair attempts, flattened the top and splined/ glued everything back together. I  made new bracing and put the body back together. The work went very well and I have been working on refinishing the body for the last few days. 

Now the "experience".

I don't work in a climate controlled environment and last night we started having fairly severe Santa Ana conditions in our area. For those of you that don't know that that means, think of hot, dry winds from the desert sometimes gusting up to 50, 60,70 MPH. 

I keep my guitars in cases. I don't keep the instruments I working on in cases. About a hour ago, I heard the Favilla "pop". Now I have two new 4 in long cracks in the body of the guitar I just finished repairing. 

Relative humidity last week ( when I put it all together): Around 55%

Relative Humidity tonight: 12%-15%

Stupid factor: 100%

You'd think I never heard of a humidifier.

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Very sad, but thanks for sharing the lesson!  A new build of mine went concave on me in a recent dry spell, because I had not paid enough attention to the excessively high humidity at the time when I did the bracing and closed the box.  It is not like I have never heard of this issue - I just didn't think it would happen to me. 


Sorry for you Ned!

Ned, You must be a SoCaler like me. The Santa Ana's really suck the moisture out of everything, and fast. Always a danger, but don't be too hard on yourself as you're not alone in suffering the results you did. I've got a Brazilian rosewood mini-jumbo on the shelf that I started years ago but have not completed due to a hairline shrinkage crack in the top thanks to those darn Santa Ana's.

Time is the best teacher, unfortunately it kills all its students.

  Thanks for the sympathy, guys. It could be worse but I noticed this morning that one original epoxy repairs that I didn't clean out and spline is also loose now. It's a set back but I will get it done... after I get it humidified. 

  Yes, Eric, I live in Orange County.  I tend to forget just how quickly the humidity level can change. I've never had a problem like this before but then I'm not exactly "high volume" in output. I make it a point to leave things alone if the humidity is high but I never thought about how fast things can dry out here. Stupidly, if the guitar was complete, I would have protected it but since the neck is still not attached I obviously don't think of it as a guitar. It's amazing how often I walk around with my brain switched off.

Ventura County for me. I too build slowly, just finished one started in '02. For the most part my shop sits at 35-40% on the humidity scale but can go into the single digits when the winds kick up. I try to keep the house closed up during those times but you really have to watch the NOAA site to stay on top of the weather. Wish I had a humidifier at times as well. 

I notice that the Favilla I'm working on is really prone to this too - let it dry a bit, and that thick mahogany just rips itself to shreds. They did select for wood, but they seem to have left it really vulnerable.

(And why don't we finish the wood on the inside of the guitar as well as the outside, eh?)

My top has been thinned down some, Mark.

 The main reason that I decided to completely refinish the guitar is that whoever worked on this before really hosed things. Besides attempting to fill the gaps in the cracks with epoxy and not aligning the cracks around the sound hole, they also did a terrible job of sanding the top and refinishing it. I'm betting they used an orbital sander but were inexperienced with it because they left high and low area all over it. It was a washboard with pits. I flatted the board by removing the original braces and damping it then clamping it down to a half inch sheet of plate glass I have. That got rid of the washboard but I had to sand it down again because of the pits. There are still a few low spots but they are small, aren't obvious to the eye and I just don't want to thin it anymore. 

My top and back are not book matched but were cut from total width boards that were not very well quartered. I don't know if that contributes to the cracking but I noticed that most of the cracks on the top were just a bit cupped on the edges like I would expect in a slab sawn piece.  Actually, for as much as I need to do to this, the rebuild has been fairly straight forward. 

One of my brothers had an instructor in college that used to tell them; "The good Lord looks out for fools and children... and none of you look like children to me".  I passed "children" a long time ago.

My sympathies too, Ned.  RH issues can certainly bite us and when they do it seems as if it's at the worst of times too, i.e. on a deadline, etc.

When I started building I had the advantage of reading on a forum that I participated with back then a story that another builder posted.  He had built his masterpiece without any RH control in his shop and all had gone very well, until one evening at approx. 3:00 AM when he heard a very loud crack from the basement below his bedroom.  And if you guessed that his brand new guitar with the first of the lacquer coats on it cracked you guessed correctly....

I took this to heart and invested in digital hygrometers which I quickly found basically sucked and if you did by chance find a digital that is accurate in the range that we like to build in (40 - 50%RH for me with bracing being done at the lower of the scale) they were not accurate in other ranges such as above 50%.

So I searched for a better solution and the Abbeon Cal hygrometers were getting great reviews so I bought one at Elderly and took it home.  As if this was not enough.... I soon learned that these things need to be calibrated every so often and you can send it to the west coast for this calibration if you wish.  Instead, or after sending it away for a couple of years I learned that a "wet-bulb" and learning how to use one is perhaps the closest that I can get to getting an actual reading of RH that is pretty accurate.  So I used the wet-bulb technique and a shop made set-up to calibrate my Abbeon for the next couple of years.  I also found that my Abbeon would drift up to 4-5% in 6 months time.....

Here is one of my wet-bulb set-ups:

This was pretty useful for my purposes of calibrating my Abbeon a couple of times a year.

David Collins turned me on to the idea of a Psychro-dyne which are available as surplus lab equipment from time to time on ebay.  The psychro-dyne is just another implementation of wet-bulb technique but without the need for an external source to draw the air over the thermometers.

So as complicated as this all sounds it does not have to be at all.  My learning curve was pretty steep but this tends to be more related to being me.... then it needed to be....;)

These days my Abbeon is mounted on an inside wall in my climate/RH controlled shop and readings are available at a glance.  I endeavor to calibrate the thing (it takes maybe 15 minutes to get out the Psycro-dyne and fire it up) twice a year and as such sleep better at night.

If this was not enough when I was looking to build a new shop and moving I selected a basement.... with a house on top where the basement is built in sand.  Kind of like a giant kitty litter box....  Anyway the sump pump has never turned on unless I manually trigger it because no matter how hard it snows of rains without any dehumidification or humidification my RH never goes out of the range of 38 - 58%.  Now combine this with a small humidifier with a digital readout and hygrometer built-in to the thing and a small dehumidifier and I am able to keep my shop at a comfy 40 - 50% year round with very little effort.  I also installed vapor barriers in the interior walls when I built my shop and I suspect that this adds to the stability.

Anyway, long story short lots of new builders contact me because of the tutorials on my site and when I am asked what Job 1 is in learning to build guitars my answer, even if it is not always initially appreciated, is gain an understanding of both wood and RH and how wood reacts to changes in RH.  Job 2 is to actually do something about it to gain a stable building environment where ever folks are attempting to build their instruments.

By the way I have personally tested at least 10 different digital hygrometers that are currently on the market and they ALL suck....  Some are as off as 15% in our desired range.  I had one that I tested that always read 45% no matter if it was 20% or not....  Maybe that one should run for political office since it tends to tell folks what they want to hear....

Lastly, for now, when we purchase that very first ever gutiar kit from Martin or Stew-Mac no one tells us in advance that we need $2,000 in special tools AND to develop a space in our homes and shops with pretty rigid RH control.... 

Thanks Hesh.  What you wrote is very informative. I've been thinking for some time that I need to find a way to better control the environment in my work area because there are a lot of days that I don't think it's safe to do much. I suppose I've been lucky since I haven't had any problems until now but I also don't really build from scratch much. Most of what I do is repair so I thought I was safer. Now I know I'm not, so I guess it's about time to get more serious about a better controlled space, at least for assembly work and finishing.

Your journey to accurate humidity monitoring/control will be a help. Besides getting a handle on my work space, I also need to build a humidity controlled cabinet for some of my instruments. I keep most in cases but I would like to have a few more readily available than that and I don't want to just leave them on stands. My wife would probably appreciate it if I gathering all the little misic instrument paraphernalia bits and pieces into a single place too.   


Whenever I read one of your replies, I feel as if I'm getting graduate level instruction for free.

I thank you sir (-:

And I sincerely thank YOU Paul - I can't tell you how many times your very valued posts have helped me out in a big way!!!

PS:  Sorry if I tend to be a bit long winded.... ;)  I'm working on it....


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