Filling Bug Holes

Like much old Brazilian this set has some flaws.  It has some small cracks on the backs near the bottom, a couple of weak spots on the sides and half-a-dozen worm holes on each side, two of which are fairly large.  The cracks on the back I’ll probably fix after the backs have been attached to the sides.
holes in sides
I’m not going to go out of my way to hide the holes, just fix them. I read somewhere recently that the existence of wormholes is a sign that the wood is genuine Brazilian; it also fits in with my philosophy that the flaws give the wood character and add to the overall beauty.

I’ve used a scraper to collect a little bit of sawdust from the sides (that’s what’s in the little plastic cup). You don’t need much. I’ve also cleaned some of the stains near the bug holes with naptha. Naptha is pretty effective at removing mineral deposits from rosewood as well (that’s the white stuff that won’t sand off, often found in trees that were grown for shade in plantations–not sure why).

back up the hole with tape Fill with sawdust glue

First I use a tiny piece of tape to back up the hole on the inside, opposite the side I’ll repair.  This keeps glue from running all over the place.  I drop a little mound of sawdust on top of the hole and then rub the sawdust back and forth pushing it into the hole, then put a tiny drop of super glue (cyanoacrylate or CA is the glue of choice here, thin viscosity). After it dries I add another drop of glue, sometimes using medium viscosity for this. I don’t use accelerator for this operation since the reaction can trap gas bubbles which turn white. Then, using a tiny sanding block (I use a tiny piece of pine or mahogany with a piece of 150 or 220 grade paper glued to it), sand flush. On the inside, I peel off the tape and then use a scraper to make the repair flush.

For the two larger holes I’ve taken a piece of scrap from the end cuts and cut tiny plugs.  The principle is the same:  push the plug in following the grain orientation, tape the back, fill hole with CA, dry, fill again, dry, sand flush.  If you see the guitar in Maryville you’ll be able to see these holes as I’ve made little effort to really “hide” them, just fix them.  But they look “right” if you will.

The last step today is probably going to seem a bit unorthodox.  I got the idea from C F Martin & Co.  I read somewhere that they, like everyone else, can always use more Brazilian and will, depending on the grade, immerse the wood in a bath of cyanoacrylate before they use it.  (That’s super glue.)  Using CA as a way to fill and harden the fibers of wood is an old repair guy’s trick and works extremely well.  I didn’t take any photos but the process is simple.  Using a respirator and working in my spray booth, I use a disposable brush to apply glue on the wood.  After drying I use a scraper and sandpaper to remove any excess.  During the process you can see that some areas absorb more glue than others: these are the weak spots.  Besides improving the strength of the wood it will also improve the tone, making the wood more rigid.  It also darkens the wood considerably.  If you plan on using an absorptive stain you should apply it before you begin this process since the CA effectively seals the wood.

 Next:  Kerfing, with Kevin Ryan’s really cool new material.

1 Response to “Filling Bug Holes”


  1. 1 Daniel Craig

    Hi, I was searching for martin guitar and I happened upon this site. Good work, I’m looking forward to more.

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