Martin back separation on new HPL model

[Brian Hart]

I'm not at my shop at the moment, but I just thought I should get an opinion or two.  I have a Martin of recent production that has the lower bout back separating from a suspected fall.  Its the HPL (laminate flooring for guitars) back.  I was going to Titebond it and apply some spool clamps.  Should this hold?  It closes nicely with little pressure.  I've had trouble with this HPL finish on the top before (simulated koa) when I had to glue a bridge back on.  It ended up needing epoxy.  

[Frank Ford]

I reach for medium viscosity CA.  Excess can be hosed off with acetone, or sanded on the corner to match the 45 degree "lack-of-binding" at the edge.

[Paul Breen]

Titebond is appropriate for gluing the backside (inside) of the plastic laminate to wood lining or braces and would be a good choice for the back to rib separation you describe. Spool clamps are fine for this. Titebond will not stick to the the front or melamine (color) side of the laminate, only the textured rear side, so don't count on it working on the outside of the instrument for anything. Super glue would be my first choice for things like bridge attachment.

Even though the high pressure laminate guitar body is essentially plastic, it does expand and contract some from swings in humidity. Also, the laminated wood necks have little or no finish on them and they have a plastic fingerboard. This can create a moisture imbalance in the neck and play havoc on your relief settings. I have been working on one of these guitars more frequently than I would care to see it that had both of these problems. The relief would not stay where I left it, even after letting it settle in a few days to be sure it had time to reach it's equilibrium of string tension vs. truss rod resistance. It would go away and 3 months latter, it had changed. The top shrunk during the winter months this year and dished in front of the bridge bringing the action down. You would think a plastic guitar would be a set it and forget it guitar but I have seen just the opposite with this one. Good luck with yours.

[Justin]

Hello Brian,

Recently I had to glue the entire back back on a Martin with the HPL.. 

Here's a link to my blog about it http://musicvillageusa.com/blogs/guitar-and-string-instrument-repai....

I contacted Martin and asked what they would use. They advised me to use original tightbond and it worked very well. I had to have a lot of open working time and tightbond allows for it. I did however have to touch up the "binding" or lack of binding as Frank says... I used CA to do this portion and it went really well.

Good luck and I hope the job turns out well.

[Brian Hart]

Thanks Justin, great blog.  Mine was dropped, yours looks like it was in a bar fight!

[Russell Vance]

Thanks for the advice and photo essay Justin, it's quality additions to our knowledge base like this which makes life easy and our repairs more professional.  Good one.

Rusty.

[Justin]

That's funny you would say that. This guitar was kind of in a bar fight. The customer admitted that he had been drinking and fell into a table while he was playing it!

[Paul Breen]

Here is an inside pic of the Martin 000CXE I was whining about. Unlike the Martin in Justin's blog, this one has a plastic laminate top as well. The Black material seen inside, butted right up to the X-brace, is another layer of the same laminate used on the outside of the instrument. How about that for a jumbo bridge plate? This one had a loose leg on one of the X-braces and it was difficult to get glue under the brace with the laminate triangles butted up tight to them. Surprisingly, the laminate top really dried out this winter and looked about the same as the dried up wood topped Martin pictured in Justin's blog. I wouldn't have guessed this could happen and told it's owner to start using a Dampit for the rest of the heating season.

[Ned Knepp]

The laminate is actually made up of resins and craft paper ( grocery bags). I would think that soaking the paper in resin then compressing it under a lot of pressure and high heat would petty much make the whole thing water proof but I've seen some odd problems with this material on cabinets over the last few decades. It seem to me that it can be affected by moisture exposure at the edges. I've never seen it fall apart even if it is submerged but I have seen many examples that appear to have swelled somewhat at the edges due to moisture. 

BTW, the craft paper/ resin build is probably why wood glue seems to work. I can tell you from experience that wood glue doesn't work so well on large areas such as a counter top.

[Brian Hart]

Update, all done.  Used titebond under heavy spool clamping, followed by lots of scraping then buffing to hide the crack and put the 45 degree edge back in the "not binding."  The mobile home countertop lives again.