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This is my first build and I have hit my first issue. I am building a D35 style dread. I noticed that my 3 peice back is starting to seperate where I have not yet glued on the mahogany support strip. It is winter here in the northeast and I have a wood burning stove and an oil burning forced air furnace. I have done my best to keep the temperature constant in my builing room. I may need to get a humidifier? The question is, can this be salvaged or will I need to replace the back and braces? My thought was to soak this area to get it to expand, then glue the strip on to hold everything in place. My concern is that it will discolor the wood. Any advise will be appreciated as i am very discouarged from this set back.

Troy

Troy,
It sounds trite, but the problems we encounter really are opportunities to learn. Keep that in mind whenever you get discouraged. I am not an expert, so read everything below with a degree of skepticism...

First off, I would not do anything drastic just yet and to "soak the area" seems kind of drastic to me. Temperature is important in your workshop, but RH is at least its equal. Get that under control and you may see the split close up again. If so, you could then wick some thinned glue into the cracks, keep the two plates pressed together somehow and let it dry. Then you could add your remaining support strips and hope for the best.

If RH is not your problem or raising it doesn't close the split, all is not lost. In that case, I would probably glue the support strips in place, then carefully remove the damaged backstrip and inlay a new section. It won't match perfectly, but if that was the biggest wart on my first guitar I'd call it a huge success. :-)

Lastly, in my opinion, no matter how this gets resolved, the most important thing to take away is knowledge as to why the split occurred in the first place. Was it an RH issue? Was the backstrip flawed in some way? Had you sanded that area too thin? What if you had not waited to add the last two sections of support strips? Figure this out and you will be better prepared to avoid facing the same issue in the future.

As I wrote above, I'm not a pro. Hopefully someone with greater experience will add their thoughts and help you sort this out.

Good luck and have fun,

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George :-)

Those look like pretty wide cracks for humidity issues. Maybe there was some stress when you glued up the back??
I wouldn't soak it...that might cause other warping issues. Just re-humidify gradually and see if the cracks close up. A box with a damp sponge will make a descent humidor for it. It might take a week or two.

Thanks for the advise guys, much appreciated. I will try the wet sponge trick and let you know what the results are. What Relative Humidity do you try to keep your shop at? Before I started this build I have researched for well over a year. To the point where the information I read started to conflict. This forum has been a wealth of knowlege but I didn't see this one coming! I should have said "frustrated" or "heartbroken" rather than discouraged. I only consider this a minor set back since it wasn't joined to the rim.

Troy

Hi Troy,

In answer to your question on ideal RH, most opinion sides on 45%. The more important issue though is that the humidity now may be very different than the humidity when the braces were put on the back and, from what I've read, (as I am a relative newbie like you, just finishing my first and starting my second) that kind of drastic swing in RH is what can possibly cause this kind of problem.

If I were you, I'd get in contact with our fellow Keystone stater, John Hall at Blues Creek. Email him pictures and ask for his advice. He's a great guy and will always help. He's saved my bacon through many issues with my first, including a 3 foot drop to a concrete floor that cracked the top in 3 places (long story!). Today, you'd never know and all looks great. I'm pretty sure he can help you.

Mike

Thanks Mike. I have been on his website many times and have read all of the tutorials. I will send him a message to get his thoughts.

You ain't gettin no professional advise from me either but I remember on my second build I made the top and carved all the braces before I made the rims. After about a week of the top sitting in a non humidified room it turned into a potato chip looking thing. Someone suggested I put it in the bathroom and hang wet towels here and there, which wasn't really a problem doing that since my cloths and towels are all over the place anyway. Yeah, I live like a viking. So.....I learnt to make the rims first and glue the top and back on as soon as possible.

Hutch

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"After forty-nine years of violin building, I have decided that the search for a varnish is similar to the fox hunt. The fun is in the hunt."
Jack Batts Maker and Repairer of Fine Violins

Hi, Troy. Man, that is discouraging. My hunch is that the back pieces shrank as they dried, thus putting a slight curve in your joined edges. If that is correct, then your edges naturally wanted to curve away from each other--however slightly. The glue you used to join the back strip to either side (and the wood itself) was stronger than your back strip, so the back strip is the part that failed. That's a wordier way of saying I agree that it's probably a stress issue--related to the wood drying out. Did you glue those edges when the shop was real damp? If so, re-humidifying the back might fix the problem. It's also possible that your jointed edges weren't absolutely straight. If your clamps forced the joint shut and then stress opened it again, it could look just like that. There's another potential fix for this, but it's more drastic: Remove the cross braces, saw out the back strips and get new ones. Let them rest in your shop for a couple of weeks to get them acclimated. Then, while the furnace is keeping your shop dry, re-joint your edges and glue the whole thing up again. And make sure the jointed edges are really perfect, with no light showing through before you glue them. I'm sure you can fix this one way or another. We have all had frustrating problems in our work. Good luck with it.

Hutch,
That is great advise about having the rim prepared before adding the bracing. I will add that to my "next time" list.

CP,
This back was actualy a factory joined back from Martin. It was from a Johny Cash style D 35. It was rejected due to a blemish along the edge which will be trimmed off after joining to the rim. The Perfling is actualy what shrunk. I can visably see the distortion of the small block pattern where the perfling seperated from itself. It is lined with a thin black strip of wood which is still joined to the edge of the rosewood.

I spoke to John Hall from Blues Creek this morning. He suggested I pop the braces off by heating it with an iron from the outside. Then pull everything back together to glue it. Well....when I hit it with the iron, it created a bit of condensation and instantly the perfling swelled back to its original form. YEAH!!!! I didn't even have to take the braces off. I need to get some fresh CA or Super glue to wick into the Perfling but I think I am back in buisness..

Thanks for all of the support. I hope that someday I will learn enough to pay it back to the new begginers.

I was confident John would get you going in the right direction! Glad it worked.

One thing to note is that this guitar will always need to be properly humidified to help fight off the reappearance of these cracks (wouldn't have been as big an issue if you had rebraced the back at the lower RH level and closed the box soon thereafter). Whatever RH level the back was braced at will be this back's "normal." When exposed to dry whether, the back will want to shrink and crack again. Glue the reinforcement strip in as soon as possible and then get it glued to the rims as quickly as you can. Once the box is closed, the back will become more stable, but just know humidity will always need to be monitored on this guitar to lessen the chance of cracking down the road. As mentioned, 45% RH is a good average for a shop. Many decrease the number to 35-40% RH when bracing to further reduce the likelihood of cracks from shrinkage. The reason stated is that there is more room for expansion of backs and tops (i.e., the back or top can increase its dome) than there is for shrinkage (there is nowhere to go except horizontally when the back shrinks to flat).

I am no expert either, but that's my 2 pennies. Good luck with the remainder of the build.

Aaron Craig

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Aaron Craig

Wow, I'm totally surprised that those strips were glued in like that. I would have bet that they would have been inlayed/routed into the back after the box was closed. Live and learn.

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Hutch

Get the heck off the couch and go build a guitar!!!!

me too! thats definitely a case of "form over function"....

You can inlay them into the back and it is a stronger way to do it. A little harder maybe. You don't do it after the box is closed. If you did that you would be routing on a curved surface. You do it after the back is glued up and not yet glued to the braces so it is flat and easy to work on.
L.

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Cut to size.....Beat to fit.....Paint to match.

The reason for having a three piece back is that they can use smaller peices of Rosewood. Martin starting doing this when the Brazilian Rosewood was getting harder to source. That is how the D 35 was born. I have been on the Martin tour three times and the story changes depending on the tour guide but that is the long and short of it.
I did end up replacing the back. As it turns out, the one piece of rosewood had an arch to the end grain. When clamped into place the arch was flattened but the stress was too much for the perfling. It would pull apart.

Troy