Martin DXM after a car trunk heating

[Bob Witte]

I have been challenged to repair a Martin DXM (HPL top back and sides) after exposure to some excessive heat while under tension.  Imagine what would happen and you'll have a good mental picture of the result!

The bridge is lifting and requires removal and reattachment, but the big problem is the newly created shape of the HPL top plate.  Depressed or caved in at the sound hole and gently rising at a 10-15 degree angle beneath the bridge nicely curving through a maximum and falling to the tail thus creating a very nice belly below the bridge.

Any thoughts or experience on how to reshape an HPL top after undergoing such an event?  I should also note there are no tone bars in the lower bout and a quick look revealed a rectangular stiffening plate attached to the underside of the misshapen top, presumably in place of tone bars.  

Any experience on a repair process or knowledge of the adhesives used by Martin to attach the bridge and the stiffening plate is welcome.

Alternatively, a confirmation of flower pot or wall art status would also be welcomed.

Thanks in advance for any assistance or recommendations.

[Kerry Krishna]

 Bob, this site is actually really good for advice from the Big Boys Who Know. I have learned so much over the last 4 years here. There have been several times every decade that I refuse projects. I have learned the hard way what to never work on. Sometimes it just comes with experience.

[Bob Witte]

I sat on this one for a while and since the guitar was valueless as it was, no hurry from the owner, I figured I could try something with nothing to lose. I used a technique when returning a curled up pickguard to proper flatness. For the pick guard, I constructed a sandwhich with the guard between two half inch pieces of finished particle board and screwed them tightly together. Placed the sandwhich in the oven for a couple of hours at about 200 F. Turned off the oven and let it come to room. Result was a perfectly flat guard that held it's shape. I figured a similar approach might work on the Martin HPL guitar. After knocking off the now barely attached bridge, I cut some particle board up to fit inside around the bracing - there is only x-bracing on these things with no bridge plate, only a stifffener - and used the pin holes to screw the top particle board to the board inside resulting in a Martin HPL sandwich. I then applied a couple of clothes irons (cheap ones that I use for veneers and had characterized for temp) side by side to the top board, turned them up to high, and left them on until everything was nice an hot. I let it room cool and disassemled my rig. Everything was nice and flat in the bridge area and beyond where the heat was applied. I used acetone to easily clean off the Martin Adhesive (they must use CA 'cause acetone works great) without damage to the HPL. Removed ashesive from the bridge and sanded it flat. I had two CA attempts using two different viscosities without success. The bridge would pop from the tail end when tuning to pitch. I then figured I'd try epoxy and roughed up the area under the bridge with 100 grit, roughed and scored the bridge bottom and attached with Gorilla Glue 42001 2-part 5 min work time epoxy. Cleaned up squeeze-out with acetone right after clamping. Two days later, put some strings on, tuned it up, and no problems. So, don't bother with the CA, just go to a two part super strong epoxy. Loctite make some dandy stuff, as well. So, there's my story. Knowing the process means that this is a relatively easy fix, so long as you don't waste time experimenting with the glues and have a couple of cheap clothes irons laying around.

[Jelle van Tilburg]

Hello Bob, 

Are there any pictures you could share with us? As I would like to see the end result (beeing curious if the heat has done anything to the finish/hpl, and what the bridge area looks like before/after, and the end result with the CA/epoxy gluing)

[Ned Knepp]

I'm curious too, Bob.  I haven't worked on one of these and don't intend to but I've spent a LOT of time working with counter top plastic laminates and learned by experience that it can delaminate under high heat. In fact it can bubble and explode if a hot pot is left on it for very long although I must say that the glue may have contributed to that..  

[Bob Witte]

Hi Jelle -
I have before and after photos I will post in a couple days when I have access to my photos. I'm mobile at the moment. The heat did nothing to the hpl, although I know that Formica countertops will blister if you get the too hot.

[Bob Witte]

Hi Jelle - 

I've added some photos.  Last one shows the top of the guitar and I have before and after shots of the bridge area.  Let me know if you have any further questions. 

[Bob Gaddis]

I think I would try a "Bridge Doctor" on it. If it works, great, if not, take it out and buy a length of electrical cord, a light socket, lamp shade and some fittings and turn it into a lamp.

[Bob Witte]

Hi Bob - I agree that a Bridge Dr was certainly a likely fix for this - thanks for you response. This actually have already affected a repair and opened this thread up again documenting the process to share with others should they encounter such a rare problem.  

[Bob Witte]

As received - sans strings.

[Bob Witte]

The cheap-two-iron-cranked-all-the-way-up heating apparatus (seriously, about $10 each)

[Bob Witte]

AAfter Bridge with epoxy attach.

[Bob Witte]

Under tension to standard tuning and setup.