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A guitar that I built in 2011 for a friend has recently experienced a separation of the soundboard's center seam. This happened as the result of low humidity. The top her other guitar, a Martin 000-28 Eric Clapton, also cracked during the same week, although not at the seam. That guitar will go back to Martin, but I've promised to fix this one myself.

My repair experience is limited, so I was hoping to receive advice on how to re-glue the center seam. I originally used TiteBond, and the finish is Ace Hardware oil varnish. The separation extends from the tail block to the bridge.

Thanks in advance,
Chris

sounds like she allowed them to get too dry,. that is owner abuse and you need to educate here about RH control.

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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

Here's one way to go about fixing your guitar.

First remove the strings from the bridge and wrap them all around the head stock.

Next hang the guitar by the head stock on a hanger and get a large, quality garbage bag such as a Hefty trash bag. Place a large car-wash type sponge in the bottom of the bag, wet. You want the sponge really wet so I typically will pour some water in the bag too so that I have roughly 8 ounces of water in the bag and in the sponge. Pull the bag over the guitar from the bottom and tie the bag tightly shut around the neck just above the neck block. This will rehumidify the guitar and let the crack swell shut over time. If the crack has not been open for very long, a few months or less it will likely close this way. For cracks that may have been open for years they don't and won't always close with this method. This will bring the RH in the bag to about 75%.

Leave the guitar hanging for about a week.

Remove from bag and wash your hands. We wash our hands when fixing cracks because we want to manipulate the crack to get glue in there. Dirty fingers make dirty, visible glue joints with crack fixes.

Examine the crack closely, you want it closed it's entire length. If it's not closed yet rebag the guitar and wait several more days and repeat the process of checking the crack.

Once the crack is closed use those clean fingers and a bead of Titebond Original (TO) and work glue into the crack while manipulating the crack from the underside with your arm in the sound hole. Pressing upwards will open the crack a bit and developing a bit of a pumping action while pressing will help work glue into the crack. The goal is to get glue into the crack and be able to see little tiny beads of TO on the underside of the top letting you know that you have used enough glue AND have it where you want it.

Once there is enough glue in the crack you need some 3/4" rare earth magnets. For a typical center seam crack on an OM or dread sized guitar 4 magnets, two sets, should work nicely. These are the rare earth magnets that provide about 40 pounds of clamping pressure per square inch.

Be careful with the magnets, they can jump and hurt you or dent the guitar. Practice makes perfect...

Have some plastic sheet available and I like stuff that is about 1/8" thick with the edges rounded and safe to not scratch the finish. Have some waxed paper handy too. Make the plastic sheet about 6" X 2".

Once you have glue in the crack place the waxed paper over the crack and then the plastic sheet. This is on the outside only.....

Carefully position the first set of magnets between the two braces transversing the center seam crack. Slide them into place from the top side using the top magnet. These magnets are used to force the crack reglue level. Repeat with the second set of magnets between the upper center brace and the bridge plate. Try to keep the two sets of magnets at least 3" apart from each other. Hang it and wait a day.

Remove the magnets (carefully, they do like to jump....) and clean up the crack repair from the out side with hot water on a soft paper towel. You want to use enough water to clean up the TO but not so much that you are getting it into the repaired crack.

Make a couple cleats, small spruce diamonds about 3/4" long, 1/2" wide with beveled edges and the grain running at 90 degrees to the top grain.

Install the cleats where the magnets were using the magnets once again to clamp the cleats across the crack.

Wait a day.

Remove magnets. Much of the time if the finish was not damaged around the crack AND if no one with dirty hands was playing with the crack the repair will not show or will require very close inspection to see it.

Notes: If the top separated from the braces spanning the crack use a syringe with TO in it to get glue under the braces on the inside when you are getting glue into the crack. Automotive feeler gauges can be useful for pushing glue under a brace if a syringe is not available to you with a large needle.

Hope this helps!

Last step get a guitar humidifier!

Here are some IPhone pics of two Martins that I am repairing cracks on this AM.

One pic, with the larger magnets, shows a center seam reglue. Note the waxed paper under the plastic caul. The plastic is also thick enough to have some rigidity aiding in leveling both sides of the crack under clamping. The plastic is also thin enough to keep the magnets close to each other but still be flexible enough to span a slight dome.

The second pic, and I am not sure what order they will appear and I can't edit photos here at work..., shows smaller magnets clamping the cleats that I glued on the inside of the box. You won't see waxed paper in that pic since there is no glue used on the outside of the instrument.

Hope this helps!

Thanks for all the advice, Hesh. I'll start humidifying the guitar when I get home tonight. I was considering to pull the bridge and sand off the varnish from the top. (Then refinish the top.) Will that help? I know it's an awful lot of extra work.

John Hall: Don't worry; I gave her an earful about watching and controlling the humidity. It's been a crazy winter, though.

The only thing I can add is this
I also have a shop full of cracked guitars. I take about 2 weeks to dehumidify them or more. If you get them wet too fast the moisture doesn't get into the lower cells.
You will know if it has stabilized if you remove the dish and let it set over night. if it reopens continue adding moisture.

_________________
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

Excellent tutorial Hesh. I'm going to save a copy for further reference. Thanks

_________________
Joe Beaver
Maker of Sawdust

I guess this illustrates the need to place a cleat or two under the top when bracing the top initially...

_________________
Steve Sollod (pronounced sorta like "Solid")
www.swiftcreekguitars.com

Any time guys - happy to help - always!

PS: Even those of us who do this every day benefit from explaining the processes to others. When we have to get our thoughts together enough to make sense to others we also have to rethink our processes AND hold them up against ideas such as could someone hurt themselves, the instrument, others, etc?

So the point is that when folks help others here the folks doing the helping are getting helped too - I most certainly am! So thanks to you guys too!!!

Steve not sure here that cleats are needed provided that one uses seasoned wood, prevents the instrument from drying out, and other box components will not suffer dimensional instability (sounds like a mental illness....).

Notice too where conventional bracing on a steel string crosses the center seam. Same idea as a cleat.

Hesh,
I don't use TB, so maybe I'm wrong, but I thought it wouldn't stick to itself? I know that is one advantage of using protein glues, is that they will stick to themselves, and you don't need to clean a glued surface to reglue it,
Mike

Great question Mike!

Yep glues such as HHG do stick to themselves and can be reactivated too and Titebond does best in a well prepared wood-to-wood joint.

But this center seam came apart when stressed by dimensional instability perhaps from the guitar drying out over the winter. Anyway it's possible and even likely that some of that seam did not get enough glue in it. There's your wood-to-wood contact and with cleats too the joint itself is no longer doing the heavy lifting on it's own.

The alternative is to clean out the crack and start new. So how does one go about this without making it worse...... ruining the finish and having to refinish the top?

In the real world Titebond is used to reglue Titebond joints all of the time.

By the way I asked that exact question long ago and got the same answer that I just gave you. Now with likely hundreds of cracks fixed as described I have yet to have one come back open. Now they just crack elsewhere.... dang things.....

You could use HHG here too but the advantages of HHG for this one in my mind do not out weigh the issues associated with not getting clamps in place in 20 seconds or so. Working the glue into the crack takes a while, may be several minutes which is too long for HHG before also getting clamps in place.

There is also the issue that we want this crack to be glued back level. HHG can jell prior to the time we take to get the magnets, waxed paper, and cauls in place. This can result in an uneven crack repair.

I usually use HHG for cracks but not when the difficulty of the fix requires more time than HHG provides as open time.