I finished a 12-string acoustic for a customer some four months back, the same type I've made several times. Last week, I got the email every luthier dreads. The guitar split both front and back about an inch right of the soundhole. These aren't cracks, mind you, but 1/6" gaps in some places.

Some info: The back is sipo, the front is sitka spruce from Stew-Mac. No damage at all to the sides. The customer swears the guitar was not subject to any dramatic temperature changes, but of course, I can't confirm this. We had some very cold weather here the week I received his email. I'm redoing the guitar free of charge, but I would very much like some ideas as to what could have caused this. I do not want to relive this again. One footnote: I made a twin of the guitar, using the same woods for another customer (in Mississippi). His is fine for now. 

Views: 402

Reply to This

Replies to This Discussion

RH control?

Most builders, including f*ctories... maintain strict humidity control through the building process typically in a range of 40ish% to 50ish%.  This combined with only using well seasoned (3 to 5 years) wood is the ticket to building instruments that can withstand to a greater degree, not totally, the dryness that comes in winters where forced air heating systems dry out our homes.

This strict range is also monitored by a "reliable" calibrated hygrometer and not the cheap-arse digitals that are inherently inaccurate.  A wet-bulb solution is the most reliable although not the most convenient way to monitor what the RH really is in our shops.

I would be interested in also hearing if the action on the instrument has changed and more specifically if the top's dome has caved in lowering the strings closer to the frets?  If so the instrument dried out for a lack of humidity control in the clients hand and/or was not built with appropriate RH (relative humidity) control during the building process.  Combine these things with materials that have not been properly seasoned and this is what we see.

There are other possible reasons as well but these are the common ones and this drying out is very typical of this time of year especially about a month or so ago when it was colder.

People who ask me about getting started with building always get the same answer from be in terms of what step one is - figure out and implement what one has to do to obtain and maintain strict RH control in the shop.  I also won't build with materials that I don't know for sure have been seasoned well.  How do we know how old the wood is that we source from vendors?  Ask them and then take that with a grain of salt...

if the finish is lacquer, exposure to extreme cold will usually be evidenced  by checking/crazing of the finish.

do you provide care instructions with your instuments and condition your warrantee based on them.


liability for the repair of an instrument damaged by cold, rain, flood, etc. is no different than a repair of damage caused by falling off a stand or the roof of a car or drunken fans.. its not the builders obligqtion to wear it.

Up here in Winnipeg it's extremely dry in the winters the 40 to 50% rule doesn't work. Customer brings their guitar in for a set up to a shop with ice covered windows, picks it up a week later, brings it home to the 20% environment it normally lives in and things start to go wrong. When I had a store we tried to keep the humidity around 30%. Some of the local builders keep their shop a little on the dry side and some don't.

This is why I don't always subscribe to the idea of rehumidifying a guitar by putting it in a plastic bag for a few days. If the customer is a touring musician and can't keep the guitar in a controlled environment then it's better to open the crack up and spine them then it is to try and close them up.

It sounds to me like the guitar went through an extreme humidity change.

I agree with you John.....I almost always do by the way.

I would not jump at taking the blame for this Guitar going bad. The customer knows what likely happend to  it and my guess is he left it out in the car on the coldest night in Febuary....But you will still have to fix it my friend. That's just the way it is .I have built guitars almost anywere including under the awning of my Trailer down in F.L from start to finish as well as the finish every year for 5 years and never had any problems with any of them. So you figger it out.  I no it would be nice to have all the modern convenances of a shop that has every thing but we all can't have it . There have been a lot of Insturments built in less that perfect  R.H   a very good number are still around yet. And I also know that  all Hell is going to brake out when some of you read this. But I still have broad sholders and I can take it. My way of thinking is the Insturment is going to be in less than perfecr R.H most of it's life and it has to be abale to stand up to what ever R.H it incounters with in reazon.  And  40 belowe is not one of them  Bill..........

I have always been careful to build dry when bracing tops and backs and when gluing plates to rims.

On one early guitar build I forgot to do this when gluing on the back.(mahogany top and back)

It was the only one of the guitars in my studio to crack, and only the back, when we got a sudden dry wind which dropped the RH to 15 for half a day,

If you are confident of your RH control during building, then the guitar is telling you it has been exposed to overly dry conditions.

Otherwise, it is telling you to upgrade your humidity control.

I meant spline btw. We've just had several days of -20c at 7am and +5c at noon fortunately the humidity is not fluctuating to the same degree.

I have read that Martin used to hang tops above the wood stove to dry them out before installing braces.  (Did they have the wood stove running all summer??)  I am just starting a Nick Lucas copy and spring and the wet season are upon us.  What would happen if I put the top in the oven at 110°-120° or so before gluing braces??  Would this help prevent this type of problem?

Ed lots of builders "bake" our tops prior to bracing but it's not done for reasons of maintaining RH control in the shop or a substitute for same.

Instead baking tops is believed by some to cause changes in the wood at the molecular level which may... help the top resist RH swings to a greater degree in the future.  Other possible benefits are that baking our tops also serves to dry up pitch making it more visible to the human eye prior to building.  The wood feels slightly different as well after baking.  

I bake, my wood that is...., for one hour at 200 degrees F weighted to avoid warping and curling.  I wait approx. two weeks after baking a top prior to bracing.  There are lots of ways to bake wood though.

But at the end of the day there is no substitute for maintaining decent RH control in the shop during the entire building process and especially when bracing our thin plates.  Letting your wood acclimate to a RH controlled envirnment prior to building is also important.  And of course only using well seasoned woods in the first place is also key to the longevity of the resulting instruments.

There are no shortcuts here and I tend to take these issues when advising others as serious as a heart attack...  When one considers that many builders will toil for perhaps a couple hundred hours to produce that first instrument AND be very deservingly proud of the accomplishment as well I'm always going to emphasize that one cannot rush the seasoning of wood for musical instruments AND strict RH control is in my view a must.

If you want to make fine wine - it takes time....  Working with wood is also something where time plays a very important role.

Maybe they were simply cold in the Martin f*ctory.... ;)


Thanks for the information and encouragement

Ed Minch

You are very welcome Ed!


© 2023   Created by Frank Ford.   Powered by

Badges  |  Report an Issue  |  Terms of Service