Email Newsletter icon, E-mail Newsletter icon, Email List icon, E-mail List icon Sign up for Finger Lakes Guitar Repair Newsletter


Show List of All Posts

Pick up and
Drop off Hours

Mon-Sat 9-5: By Appointment

Splint Martin Top Crack

May 7, 2013

This article was featured in the Finger Lakes Guitar Repair Newsletter.  Sign-up for the free Newsletter today!  Just type in your email and press Go in the left hand sidebar.


Martin Guitar Spruce Top Martin Guitar Top Crack
1. This Martin Guitar got pretty dried out.  The spruce top has developed a long and wide crack that extends from the belly of the bridge all the way to the tail-block.  This open crack won’t stay closed, even after the guitar’s moisture content has acclimated to a relative humidity of 50% at 70 degrees. 2. A Simple Repair consisting of working some glue into the crack and cleating it won’t hold up in the long run.  Instead, I’ll inlay a thin piece of spruce, or “splint” into the crack and reinforce the repair with some cleats.  As far as Martins go, this is a cheap one so I’ll have to do a stable and good looking repair fast.
Even Crack Width with Razor Blade  Rough Shape Cross patches
3. Preparing the Crack.  I’m dragging a razor blade through the crack to dislodge any loose wood-fibers or gunk and ensure that the crack is a consistent width and taper throughout its length 4. Cleats, also called cross-patches are little diamond shaped pieces of wood that are glued to the inside of a guitar.  The wood-grain of the cleat is glued perpendicular to that of the top.  I’m shaping the footprint of the cleats with a sharp chisel on my end-grain up cutting board.
taper thickness of cleat guitar crack repair roucgh thickness sand splint
5. Beveling the Cleats only takes a few minutes with a sharp chisel against the fence of my bench-hook.  The idea is to reduce the mass of the cross patch by tapering its thickness from the center out to each of the 4 straight sides.  I’ll glue the cleats to the top with some fresh Franklin’s Original Titebond which has a moderate initial tack and a long open time. 6. Thickness Sanding the splint with the luthier’s friend sanding station on the oscillating spindle sander brings the thickness of the spruce to an even .015” thickness.
trim splint sand splint to final thickness and taper
7. Trimming the bottom of the splint with a ruler and razor blade. 8. Fitting the Splint with some 180 grit psa sandpaper attached to the flat granite slab.  The downward pressure of my stationary left thumb creates a slight taper toward the bottom of the splint as I pull the splint with my right hand.
test fit splint glue splint with ca
9. Test Fitting the Splint.  I’ll sand and test fit the splint until I have a good fit throughout the crack. 10. Gluing the Splint once it’s in place with super glue is quick and easy.  This is a lower end Martin and as such, it has a “hand rubbed finish” which will tolerate the acetone needed to clean up the excess super glue.
 trim protruding splint plane splint flush to top
11. Trimming the Splint with a razor blade gets rid of most of the protruding splint. 12. Planing the Splint flush to the top of the guitar will complete the repair.  I’m using my Lie-Nielsen #101 violin maker’s block plane which I’ve set up with a 55 degree cutting angle and adjusted to take as thin of a cut as possible.
top crack repaired with splint repair looks good
13. A Splinted Crack.  The repair is visible but it looks pretty good, even up close the repair blends in with the surrounding wood grain. 14. All Done.