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Another request for help.  I have been playing in a band locally. Last night a kid (mid 20s) came up and started talking. He wanted to jam a bit after the gig. He had just returned from a tour in Afghanistan. Anyway, he had a Martin Model:000CXEBLACK I believe. About 5+yrs old, bought it 2nd hand 2-3 yrs ago. I first noticed 2 steel 5/16 bolt heads in the bridge, then when I looked closer the bridge was lifting so much you could see the bridge pins. The area around the back of the bridge in the soundboard was warped upward as the bridge lifter, before it separated. This guitar is made of what some quick research shows as Martin's HPL material.

The kid deserves a break, he's quite the musician and is trying to fit back in, get a job after his service for us. I want to fix this guitar for him...he's in love with it. I don't have a picture...yet.

The guitar needs a bridge plate and a new bridge. BUT, How can I flatten the 'hump' ....compression under heat? And what glue, epoxy? There didn't seem to be any sign of glue under the lifted bridge....but what is this black composite material?

Jerry

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For what I've seen until now, if you sand the area to glue to remove any shiny appearance, wood glue sticks really well to that material. I've never tried to flatten this material, maybe some water and heat. I don't think it can hurt...

 Well Jerry I don't no anything about that kind of material but the way I fix the hump I will put a hot wet rage on the inside just back of the bridge plate for about an hour then I take a piece of 3/4'' plywood about 2" wide or so and what ever length you can get between the x braceing and a larger one for the top. I then take my old iron and I get the two pieces good and hot put a piece of tinfoil on the top under the plywood and clamp it for a day When i get the hump out I go to work on the bridge plate likely add a piece behind the OR. plate and do an overlay over the entire B. plate .You will likely find the B. plate  is to small and that was the problem or to thin. P.S. I am sure that someone will have a better plan Good  luck Bill............

This HPL is weird stuff. As I research it the HPL is compared to Formica! This Kid bought the name 'Martin' sad to say...only the neck was worth the name. But the dang thing made it thru a year in Afghanistan with 2 bolts holding it together!

Would you add heat (I have a bridge plate heater made of 1" alum I usually heat up with a clothes iron) inside and use a flat plate on top, clamping the 2 together? Or heat outside with support inside?

Jerry

Jerry, I haven't worked on any of the guitars made with this material but I spent a LOT of time applying it to cabinet tops. I wouldn't add  much in the way of heat to the hpl. It is, at it's most basic, many layers of a paper product, impregnated with a resin, compressed under very high pressure and heat into a very thin sheet. That is covered with a thin layer that contains the "look" of the sheet with a thin clear layer over it for protection. In short, Formica/ wilsonart/ plastic laminate. It is the same material that's been in use on kitchen counter tops for decades. It is NOT heat resistant and isn't particularly good at conducting heat so it is possible to de-laminate it with enough heat, say a hot pot setting directly on the counter top. I have see blisters and even an explosive rupture once that directly resulted from this.

The stiffness of HPL, from tail block to head block, is nothing like what you would expect in spruce or even cedar.  If the top is pulling, I'm guessing that the uinderlying bracing is to blame. It's completely possible that the glue in the bracing has been affected by the heat of his living environment so I think you should take a good look at the glue joints between the braces and the top. The HPL should be very easy to press/pull back into shape. In some ways this may have been a very good choice for him to take to the Afghanistan. A wood guitar may have suffered much more than this one. 

Neither heat nor moisture will have any effect on the hump; don't bother. There is a large reinforced area that helps resist the torque of string tension, but it may be loose or broken. I don't think there's much you can do about that.

The bridge should be glued with thick CA; this is what Martin uses and is the only thing that will stick to the HPL surface. If you want to replace the bridge you will have to get one through an authorized Martin repair center.

Just heard a good recommendation for a specific medium viscosity CA that Martin uses to paste the bridge back on - SCOTCHWELD PR600 from 3M.  It's a slightly flexible version that supposedly resists cracking off as easily as the regular stuff.  Depending on cosmetics, I'd reuse those bolts or replace them.  And, for structural stability y, I'd consider a solid reinforcement below, too.

HPL although obviously impervious to  moisture,  certainly does react to heat, and can be made malleable by the application of heat.

How do you think they roll postformed edges onto HPL countertop laminates ?

 

It's true that they apply heat to the plastic when they roll the edges and back splashes on countertops. It should also be pointed out that the laminate used for this process is approximately half the thickness of the regular countertop laminate. I don't know how this stacks up to the HPL used by Martin in their guitars but I think that Martin is using a heavier  HPL in their construction. 

Heat can be applied to almost anything and it will help it bend but is it called for in this instance? My personal opinion is that it is not needed. The heat that is used on a rolled counter top is used to help make the top material a bit more plastic to relieve the stresses caused because of the degree of deformation needed. In the case of a bulging top, you just don't need to move the material all that much so rather than helping, the heat could do more damage to the glue joints between the top material and the braces.  

Ned, the laminate used on postformed countertops is not vertical grade laminate, it is regular full thickness countertop laminate.

 With the application of heat, the edge  gets rolled in 2 meter 3 meter or 4 meter lengths, to a 20mm radius (for a 40mm thick countertop, or 15mm for a 30mm top which is uncommon these days), and is then glued (with normal white PVA glue ), to the particle board substrate which has a corresponding radius machined on the edge..

 

I am of course talking about European style tops here ...when I worked in cabinet  shops in the States, I was introduced to the rolled backsplash, which quite frankly, nobody in Europe would entertain, because it means that you can only mitre the countertop with a 45 degree miter which is unsightly in the extreme. With a flat postformed countertop, you can use a mason's mitre which looks far more elegant.

 

But I digress ...

Ok.

 When I was in the business it wasn't like that here. The HPL that was used on rolled edge counter tops was very thin. Contact cement was the order of the day.  I tried to lay a counter top by hand once using some of the HPL meant for rolled edges. It was VERY flimsy.

Maybe it's different now but that is how it was when I was doing it. All I can continue to say it that I've never seen any HPL was so stiff that a bulging guitar top would require heat to get it back into place. 

Frank, any suggested plan B med CA? The pr600 sells for $21 per 2 oz bottle....not bad but suppliers sell a min. qty of 10 bottles!

Jerry

I have re-glued four or five bridges on Martins with the HPL tops. I contacted Martin to ask what type of adhesive should be used, they did tell me to use a medium viscosity CA. All of them have held up very well and none of them have let go yet. As far as the "bellying" of the top, I'm assuming it is like some of the others I have worked on, where there is a HUGE I guess you would call a bridge plate on the interior, but much less bracing then normal.. I have never tried to repair that problem on one of these, but I would think about doing some sort of overlay to the existing bridge plate. Maybe maple, or rosewood? With a little larger footprint than usual. My thoughts are once you get the bridge off, if you do an overlay and clamp it flat, that might help to flatten the top out some what........

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