Martin mahogany back separation- dried out.

[christopher smith]

Greetings all- the new guy here- just discovered this forum and have tons of stuff to discuss. OK- first off, got a mahogany bodied Martin D that dried out resulting in a split back. The center seam is tight at the very top and very bottom- but in the center, there is a spread of maybe a mil or so. How do I repair this without making it worse? And yes, the back is loose from the inside back bracing about 2 inches on each side of the split- there's a small amount of movement on either side of the back braces when pressed from the inside. I suppose my big question is if wetting it for a while doesn't close the gap, what would be the best filler to fill the crack with?

[Roger Häggström]

This is a major repair if you want to do it the right way. The bottom off and some serious gluing of the bottom braces and possible a filler strip between the two bottom halves.

But you can always do a working simple repair, it's in the back and the tone and playability of the guitar don't depend on a really good repair. Some hide glue for the braces and a putty of hide glue and mahogany dust to fill the crack will work just fine. The putty will be darker, but it's on the back... it can be a temporary 20 year fix. Using hide glue the next real repair will not be a problem (not so with modern glues) :-)

[christopher smith]

Thanks Roger- I considered a filler strip like you mentioned but the thought of removing the back scares the stuffings out of me. I appreciate your reply and will certainly ponder your advice.

[Paul Breen]

Pulling a back off for something like this is WAY a last option.

You need to first try re-hydrating the guitar and see if the crack will close. Do you have an instrument humidifier, like a Damp-it or similar? It's OK if you don't don't, you can use a sponge in a perforated plastic soap container or perforated plastic bag, just not dripping wet. Anyway, put a humidifier in the guitar, put the guitar body in a plastic bag large enough to fit it, no need for the neck to be in there. Put all of that in it's case and leave it for several days. If the humidifier dries out before the crack closes, re-wet it. It will absorb the moisture at it's own rate and you should know after 3 or 4 days if the crack will close on it's own. I have left them up to a week and a half like this. I have also forced the issue on a few occasions and literally painted the cracked part with water. Use a paint brush and do the entire back evenly. You don't want puddles of water but I work fairly wet when I do this.

If the crack closes up, your job just got easier. Glue up the back crack first and do the braces last. Install cleats for extra insurance, do this before the brace work as well. I won't use anything but hot hide glue for crack repair but lots of repair folks are happy enough with the results from original Titebond too. Hot hide will actually pull a joint tighter when it dries, glue joints are minimized visually and the clean up is a snap. Whatever you end up using, the challenge is to get the crack lined up, held in place and clamped. Work out your clamping strategy before you apply glue.

I posted this guitar a while back, that also had a stem to stern back crack, and few others. All the back braces loose, which made gluing the crack a bit easier to manipulate. This was just bagged with a humidifier inside and left to sit for a week. The cracks where so nicely closed, I did not need to clamp across the back to pull them tight. Your guitar may respond in this way.

http://fretsnet.ning.com/forum/topics/trojan-horse-guild-12-string

You'll see from the pictures that I use magnets for hard to reach braces. If the brace ends are solid, you may be able to clamp lightly from the outside enough get the job done. I don't know what your skills are or what tools you may have but this is how I generally go about it.

[Roger Häggström]

What happens after the guitar is humidified, the crack is closed and glued as you describe? Can it be dried out again without having new cracks appearing? Or does it need to be kept in humid conditions at all time?

I guess the glued crack will hold and if it was a weak spot the guitar will stay crack free. Maybe the water that left the wood and made it shrink to a crack can be refilled to the same state as before the drying out. Some structures in the wood may not be as easy to refill though.

[christopher smith]

Thanks Paul, we're thinking along the same lines here. It should be not such a traumatic operation to repair this split and it's not like it's a crooked break or anything. My biggest problem is patience- I get in such a rush to see things happening that I fix one and break two. thanks again man.

[Greg Mirken]

It may take a couple weeks, but I bet it closes up fine. I wouldn't use hide glue on a joint previously glued with aliphatic resin glue.

[Paul Breen]

If it is a center joint failure, Greg makes a good point and you should use Titebend. If the split is adjacent to the center seam and fresh split wood, use either choice.

Roger, it is a matter of stewardship. Swings in temperature and humidity can do bad things to wood. The worst times are warm moist winter days where the temperature suddenly plummets, fast change. That is why repair people see up swings in crack repairs mostly in the winter. It is up to the owner to pay attention to the humidity swings and take an active role in protecting their investment. It is simple, just keep a Dampit or the like in it when the furnace season starts, check it every few days and refill it when it's almost dried out. A humidity gauge is a good idea if you don't have whole house humidification or travel a lot from humid areas to arid regions.

Bob Taylor generously shares his knowledge in a few videos about the effects of humidity on guitars. The first one here:

https://www.youtube.com/watch?v=tB8tELj43RE

Christopher, good luck with the repair, this is not a beginner fix. Don't be shy about taking it to someone that has experience with this type of work, if you have doubts about your ability or lack the proper tools and repair chops.

[Roger Häggström]

Thanks.

Yes, dry winters can kill a guitar. I use humidifiers in my apartment and in the shop in the winter (and a dehumidifier in the shop in the summer). Spend a couple of hours yesterday looking up the method, I have already seen the Bob Taylor videos :-) Nice to learn a new thing. If I ever get a modern cracked dried up guitar on my bench I will try it out for sure!

My only concern with the method is that the guitar may be a humidifier junky after the perfect repair. With new wood in the crack or a reglue of everything in dry conditions it will cope with dry winters without having to bother with humidifiers and cases. With a domed top and bottom and gluing the guitar in dry conditions, dry winters will be less of a problem. But that's something you can do only when the guitar is made.

I do have a patience problem, I admit that. I'm slowly learning that some things can't be corrected right away...

[Steve Denvir]

So this may be a stupid question, but if you rehumidify the guitar and close the crack, how do you glue the crack? Beyond cleating the inside, I mean.

[Hesh Breakstone]

Hey Steve. It's edge glued and we use rare earth magnets, big, honking ones in shop-made teflon flattened fixtures to keep things level and to prevent our magnets from being glued to the work piece. Our 3/4" rare earth magnets exceed 40 pound of pull each. These things can also hurt you if not careful or if wearing metal belt buckles.........

If a crack has been wide open for too long they generally won't close all the way and/or won't stay closed. I don't want to be redundant with what Paul said because I agree with all that Paul shared.

What I did want to mention though is we rehumidify at around 75% for up to three days and can force most cracks closed but then we let it hang at 45% for a couple days to see if it opens back up before proceeding.

Reason being we can force a crack closed, usually, but we also don't want to glue and cleat and create stresses that will crack somewhere else the next time the instrument is abused in the low RH sense.

When this is the case it's better to fill a crack than force it closed and create stresses elsewhere.

We repair many, many cracks this time of year in our Michigan shop because our furnaces are on and our clients don't always understand that wooden musical instruments need to be kept humidified.

Don't know it this has been mentioned so I will. Martin has a wonderful warranty for their clients but they don't, understandably cover abuse and issues from letting the instrument dry out. This is one of those....

Lastly good ole Titebond or Titebond "Extend" which still sounds like a marital aid to me... work great for this kind of crack and no one has to jump through hoops with short open time.

Lastly if a crack is open too long it can and often does result in permanent dimensional instability in the structure. This is again when filling and not creating more stresses may be prudent.

[Christopher Parker]

Hesh, where can I get some of those big magnets? And the supplies for the teflon fixtures?

[Hesh Breakstone]

Hi Christopher you can find rare earth magnets on-line and we use the 3/4" and 1/2" ones.  You will know you have the right 3/4" ones if they have pull of around 40 lbs.  They are pricey too.

The teflon came from a local Steel producer who has a retail store in A2 (Ann Arbor) and they sell cut offs of other materials as well as metals.  They are unreliable for always having something because of the nature of cut offs and how they are produced but you can find teflon on line I am sure too.

The teflon is not required by any means.  I also use waxed paper first, to contact the glue and clear plexiglass after that to flatten the seam followed by the magnets.

Do be careful with the magnets they are rather dangerous.  They jump if you are not used to using them and they also are known to chip.

Where magnets excel for our purposes are for things such as a back seam where clamps can't be used or for applications that are out of reach.  For out of reach things we often can connect two magnets where we can reach and then on a bed of plexiglass and waxed paper slide them into the place we can't reach.  Be sure to cover the inside magnet with waxed paper so it does not get glued inside the instrument....  Don't ask me how I know about this...;)  With waxed paper on the inner magnet you can slide them back out and into reach again..... usually...... ;)