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]

One other thing with rare earth magnets that is good to know is that they can leave round black stains on wood if they are wet (from hide glue for example). Always have something between the guitar and the magnet.

[Paul Breen]

Steve, after the crack is closed, you work glue into it. I just reach my hand inside and push up and release repeatedly below the crack after having slathered the split with glue. I check before applying glue to see where I can reach the crack from inside. Places I can't reach, I'll use a bit of dowel rod or make a "V" shaped plywood lever that pivots off of the back and pushes up on the top.

When combined with Infra Red lamps to keep things heated up, you will have plenty of open time with hide glue. Mix it a bit thin, apply it liberally and work that in as mentioned. Wipe off  the excess with a damp paper towel and repeat this until you see glue coming through on the inside. Unless you have some very elaborate clamping strategy, you will have plenty of time to get things buttoned up. Too elaborate of a clamping strategy would also be a problem for Titebond, so keep simplicity in mind when figuring out how to get the crack clamped. With hide glue, you don't have to worry about glue clean up to get clamped up. Wipe off the excess with a damp paper towel, clamp and let dry. Whatever glue residue is left is easily cleaned up later using a soft rag, wrung out with hot water. 

White paper reflects the Infra Red and those places will not heat up.

I have clamped up many cracks with out the need for magnets just using light clamping pressure as shown here. (There are some images of magnets used for alignment in the link I posted earlier in this thread.) If the braces inside are completely loose, this may or may not get the job done. As already mentioned, work up a clamping strategy before you glue!

I like plexiglass because you can see through it and monitor the alignment and the glue won't stick.

This is usually an effective way to go with archtops.

If you need to clamp across, from bout to bout, it may look something like this.

My most frequent use of magnets is for brace repairs. I use 1" X 1/8" magnets and stack them to get more or less clamping power. I bought them on Ebay for less than the on-line supply houses. Here is an image showing how I apply them inside and outside of this same Washburn archtop. The finish outside is protected with scraps of leather, cut up for this purpose.