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Hmm the buyer of my first sold guitar askt me over for a coffee, I went there, and saw my beauty BUT I also saw something he had not seen, a crack from the lower bout to the bridge ! . The thing is - I had told him the as he ordered the guitar, and everytime we spoke on the photo etc that he really needed to get himself a humidifier as the top on the guitar is real thin and will not stand a humidity of 30-35 over the winter. So he knew this. still he never bought a humidifier and had the guitar standing freely in the room. So it really is not anything that has to do with construction or something I could help prevent. He is totally ok with this. So he even ordered me the tools I need to fix this with from Stewmac. The guitar is french polished.

The only question I do have is - As the crack seem to end right by the bridge, do I have to take the bridge of, or should I simple fix it without taking of the bridge ?
here are the tools I bought with On the photos you can see exactly how the crack looks ! allthough It dontseem to go under the bridge.
[url]http://www.stewmac.com/shop/Tools/Knives/PowerKnife.html?tab=Pictures#details/url]

In a way I am happy it happened. Now I get some repair training to !!!

this below is the gitt that got the crack .

Lars

When I sell a guitar I make it very clear that Humidity issues are nothing I can control , so the buyer needs to control that part . Most cracks on the top are from Humidity. Martin no longer will repair humidity issue problems . It is not easy to tell but my money is that this time of the year it is humidity , ask your client if he used a humidifier , and also feel the top before you ask. If the top feels like corduroy it was most likely humidity.
These kind of cracks can be repaired with re hydrating the guitar , letting the crack close and working h h g into the crack .

_________________
John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

If one day I would sell one, this would be my nightmare.

Not to completely hijack the thread...but just out of curiosity, how thick is the top? I've heard over and over that top thickness doesn't have anything to do with cracks appearing in the top...but I can't quite believe it. My personal theory is that humidity fluctuations result in dimensional changes in the back and sides and that these changes effective push or pull on the top, which can cause cracking.

Just to illustrate the forces at work here - the ancient Egyptians used to use wood dowels to harvest stone in rock quarries. They would drill a hole, pound the wood in, and then just add water. The pressure from the growth of the wood would literally split the stone from the mountain...!

Best,
Trev

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http://www.PeakeGuitars.com

As John describes you probably do not need the SM tool. If you rehumidify the guitar for a few days you should see the crack close and it can then be glued back together with HHG or TB1. You may need to glue a couple of cleats underneath.
If you need to splint it's better to take the bridge off, and make the splint go under the bridge as it has more chances to be invisible that way. Even then the SM tool is probably not needed.

_________________
Laurent Brondel
West Paris, Maine - USA
http://www.laurentbrondel.com/

Also Lars bro let the client know that the guitar needs to be in a case with a case humidifier if it's not in his hands and he is not humidifying his room or home to the level that guitars (and Hesh.... ) prefer.

Trev I watched that too about how they quarried rock with wet wood -fascinating!!!!

Actually, the same day I saw the crack he ordered a humidifer. He has a small apartment so I think he will can make it with this humidifier, he also ordered a good Humid...meter from Stewmac. So, hot hide glue or titebond1. Sounds great to hear I probably dont have to use this little chisel thingy, instead just squeese in some glue in the crack. the humidity we had this morning was around 33. so its really dry here.
John He was told by me to get a humidifier lots of times before I had finished the guitar. I told him this was a must for the guitar ! ( he is a friends of mine and there are absolutely no hard feeling) infact It went like this- Hey Tommy have you seen the crack on the top, - WHAT - Yup ! _ hmm crap, well thats the way it is, you want some more coffee. always. and that I told him I´ll have it fixt for him for free as Its good practice for me. and he´s my friend since 15 years back. ( my guitarteacher once).
Hesh I just remember, got him to also order on of those bags you hang on the strings in the case for humidifying. so now he is fully armed for the next time.

I will post a shot of the top before and after. so you all can tell me what a crappy job I did .

Lars.

It kinda makes me wonder if a person is building a guitar to live in a part of the world where the humidity gets very low one might want to bake the top to dry it out as much as possible? I guess I'm lucky living on the Wet Coast. We don't seem to get the drastic humidity changes.

Way to make lemonade out of lemons Lars!

Good Luck,
Danny

Lars-33% Relative Humidity is not that dry! In houses without humidifiers in the 'cold' parts of Canada (and Sweden??) the RH can be in the 'single digits'. It's tough to get the RH above 20% or so in winter in many homes without very good (triple-glazed) windows- there will be water running down the walls!
Moral- We're lucky to be living near (unfrozen) water. (Like Danny, I live on the Pacific coast- RH is about 40-50% all year long).
Moral #2: Be careful selling guitars to folks who live in deserts or cold climates.


That's a beautiful guitar, BTW. That little crack repair will just give it a bit of the 'vintage' look.

Cheers
John

An RH of 33% doesn't seem terribly low to me either. A question for the experts: Is there something else that might cause a crack like this to open up?

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George :-)

This top had been air dried for several years. and I had it in my shop for several months before workin on it. So I am almost positiv the reason for the crack is humidity. I have my humidity set for 45% that at times goes up to 50 % . So as the guitar came to my friend with a humidity of 30-35 % and stayed like this for a month I cant think of anything else than humidity as the reason for the crack ? my other guitars with tops from the same tree are all ok. (2) .

As a side-bar to this discussion, I've always heard that it's best to leave the guitar in the case unless playing - to minimize these types of problems. Is this true?

BTW, I saw a guitar in Guitar Center that had an identical crack to what you described. A Martin. They had it deeply discounted, and I almost bought it.

Humidity of 30-35% is high for winter time in heated space unless you are running a humidifier....

It may be 30-35% humidity OUTSIDE when it is -5C and you have snow on the ground -- You could easily end up with humidity in the single digits (5-9%) indoors when you are heating... unless you run a humidifier.

My guess is that the fellow was running his heater in the apartment.... Cold weather is upon us.... and heating up that extra-cold air made the apartment extremely dry. Does your friend have trouble with chapped lips, bloody noses, cracked hands in the winter?

Personally... The guitars I like to play stay out of the case... They get touched more this way.... BUT the case does serve an important function... It keeps the guitar from getting massive damage when my wife knocks it over...

Thanks

John

How thick was the top Lars? Thin tops are more prone to cracking as they can't take the stress of low humidity changes as well as thick one can. I try to keep my tops as thick as i can. Usually thicker than .110

Adding the humidty might just close it up completely with very little or no visual issue. Depends on the size of the split.

I'm not really a luthier...but what I have found is that some wood cracks and some don't. Humidity plays a factor...but when you have braces with grain in one direction and top and back grains going in another direction, even when they are assembled at a desired humidity range, Sooner or later...something is going to give. It's just a matter of time. Grain will expand and contract much more in width than in length. So, the 2 don't really go together without stress. Keeping humidity, heat and cold fluctuation changes to a minimum is crucial to a mixed grain directional wood item of any kind. I suppose a top thickness could be a factor as the directional stresses are in play. The weakest point is what gives. Also, certain woods have different expansion rates. Some more open grain woods expand and contract very quickly and can't handle quick environmental changes. Others do better.
Cracking will always be a issue with instrument makers and anyone who creates in wood. It's just a matter of when it's gong to happen. The better the care...the longer you can hold it off.

That is a beauty guitar. All OLF the suggestions should make for a clean and reasonable simple fix.

Kent

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EXCELLENCE IN SCULPTURE, CARVING, LUTHIER, ARCHITECTURAL MILLWORK AND DESIGN

http://www.kabart.com

Lars as others have said the thickness was not an issue. I have guitars living all over West Texas So places the average RH is 20-30% and it is common t have dipps in to the single digets during the winter If humidity was the issue I would expect to see srinkage at the purfling and binding joint on the top before I saw the top crack. This is not always the case but most of the time is.

Will examine the guitar beginning next week. and then I will see it more clearly.

lars

Hey Lars, you really need to calibrate your humidifier!!! My digital hygrometer starts reading at 6%, and if I dont have the humidifier running it drops to --. Thats less than 6%. With the humidifier on i can hit the low 30s.

Sorry to hear bout the crack bro. As other have said, humidify the guitar until the crack is really tight, then glue.

-The other Lars

Hi Michael, could you explain a bit more about your philosophy on this? I have heard this same line of thought from other accomplished builders but I can't quite accept it due to the idea that if all kiln dried tops were made 1.00" thick, then they would never crack. So, thickness must have an effect on the crack resistance of the top. I also suspect that if we studied crack propagation in wood we would find that as with other materials, there always exists some number of "micro defects" within any one piece and that these small defects are where the cracks propagate from (this is in line with my understanding of crack propagation in composite materials). If the thickness goes below a certain value then the integrity of the part as a whole would seem to be compromised.

Best,
Trevor

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http://www.PeakeGuitars.com

A guitar top should withstand 30-35% humidity without cracking. Either this guitar was subjected to much lower humidity levels than that for a significant time or somebody dropped it. I'm anxious to hear your conclusions once you get a look at it.

I think wood "seasoning" is a big factor. If a top was cut in the last few years, it could be unstable even if the humidity of the wood was less than 6% when used. Something like the wood baking box Todd showed in another thread could be very helpful if you are using tops where the tree to guitar time is low. It would be interesting to have your friend measure the humidity in his house when he gets his hygrometer. I bet it was a lot lower than 33%.
TJK

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It's not what you don't know that hurts you, it's what you do know that's wrong.

I did not say that a thin top would not crack. I said I would expect to se signs of cross grain shrinkage if humidity was the issue.

Lars, Like alot of has said, thickness could very well be an issue.You still haven't told how thick is is.

I would say its about 0.090" But its built with a lattice bracing pattern beneath the main X.
The guitar before this one is built the same way 0.090" , with a top from the same log of wood, air dried for several years and is in still in perfect condition.

Lars

Wow Lattice bracing and it cracked behind the bridge????? How many Xs' in the lattice Also .09 is not that thin of a top. roughly 2.3mm