Molded Caul For Guitar Headstock Crack Repair (Pt. 1 of Gibson ES-225 restoration)

You may recall I am finishing up the Ovation guitar neck reset.  I'm actually waiting for some more lacquer to dry on the chip fill, so I started in on another project.

What you see here is a late-1950s Gibson guitar that has a break and crack in the headstock.  Guitars with tilted-back headstocks are prone to these kinds of breaks.  By its nature, the scarf joint on this type of headstock is weak, and if the guitar is dropped or falls at the right (wrong) angle, this is what happens.

Gibsons are notorious for this - try an interweb search for 'broken Gibson headstock' and you'll see what I mean.

In this case, the break is not severe and it can be repaired easily.  The crack curves across the headstock and the top of the neck.  Dan Erlewine refers to this as an "evil smile."  This split goes about a quarter of an inch deep or so in the center, and is shallower at the ends.

I bought this guitar as a 'project' - in addition to the crack, it's been stripped of all its hardware.  Which is a shame, since this is a fine instrument, as we will see.  Fortunately, all the original vintage-style hardware bits are available new.

I can gently open up the crack, so the plan is to inject hot hide glue into it and clamp it shut.  The repair should be extremely strong.

Since part of the crack is on the curved part of the head where it joins the neck, I'm going to make up a custom caul to fit the neck exactly.

I got this technique straight from the great Frank Ford's site.  I'm using a product called "Tuf-Carv" to make the caul.  It's a polyester/epoxy repair material that sets quickly and will take the shape of whatever it's molded to.  And after it dries, it's like wood.

The Tuf-Carv is in two parts: a polyester resin, and a hardener.  You mix them together, and whoosh! you slap it on, it hardens, and you have your mold.

A couple of notes:  the amount of hardener will vary the time for the stuff to set.  I probably used too much - my mold was set after about 5 minutes (the package says 6-12 minutes set time).  Second, it smells awful - wear a mask and mix and use it outside (I did neither so I am an idiot).  Third, it's really gloppy and will glop all over the place if you let it.  Cover your workspace!

I couldn't get a shot of the stuff while I was mixing it, but this is what I did:  I put a piece of cling wrap on the guitar neck.  Then I mixed the Tuf-Carv on cardboard, then transferred it to a hunk of wood.   Then I plopped the thing on the neck.

I pressed the wood down, held it for about 5 minutes until it set.  Then I let it dry overnight.

You can see how it took the shape of the neck.

And the next morning, I have a guitar neck-shaped mold to use as a gluing caul!

Next: injecting hide glue into the crack. 


The entire ES-225T project:
1. Starting - making a custom moulded caul for headstock break (This page)
2. Headstock break repair using hide glue
3. Filling headstock crack pt 1
4. Filling headstock crack pt 2
5. Repairing divots in top
6. Installing the tailpiece, bridge, enlarging tuner holes
7. Making a bone nut
8. Installing tuners, and wiring
9. Installing nut and pickup
10. Completed - photos of completed ES-225T
Updates March 2015:
11. Bigsby B11 Installation, Pt. 1
12. Bigsby B11 Installation, Pt. 2