Side Crack Repair on 1919 Gibson A-4 Mandolin

When we left our vintage old Gibson A-4 mandolin, it was waiting for yours truly, the awful of this blog, to cook up a caul to use to press down the side to fix a crack.

Let's get with it, shall we?

You may recall my trusty jamb saw from the adventure I had last summer fixing a rotted piece of a wood pillar on the outside of my house.

The top of the mandolin is lower than the fingerboard, so I'm making a caul with a triangular section of a wood block cut out to allow it to sit on the fingerboard, but also have a part that also sits on the top - basically two levels at once.

Since I don't have a bandsaw, I used the jamb saw to make one vertical cut for the long side of the triangle.

And then I made a horizonal cut with the saw to cut away the triangle section.

You might see where this is going.

The piece I cut off allows the caul to sit up on the fingerboard and also has a section that will contact the top.  I decided to cut it on an angle so it would fit along the neck better and not want to slide off under pressure.

I thought I'd want pressure on both surfaces when I clamp it up.  Pressing down on the fingerboard alone doesn't close the crack on the side much.

I like to use cork on the surfaces that will touch the instrument, so the caul won't damage the finish, and it also helps it not to skid out of position.

So I glued some cork to the bottom surfaces.  You can see that, ironically, I used another caul to help clamp the cork down.

Almost ready.  I just need to trim that excess cork on the belt sander.

I'm also going to round the edges a bit more...it looks more finished and not so crude that way.

I actually like making cauls.  You get to be a bit creative and use the problem-solving part of your brain at the same time.

Sanded flush.  You can see the triangle section clearly now.

Trial fit on the mandolin.  Should work fine.

If you're wondering about that bad spot on the side, well, I did sand that smooth later.

You can see that there will be pressure on both the end of the fingerboard and the top, which we need in order to close that crack on the side up as much as possible.

Aside: lookit how tarnished the tailpiece cover is.  I need to polish that thing up.

Now back to our crack repair.

I used a couple of my removal spatulas to open the crack up as much as possible to get glue into it.  Sorry about the bad picture - it's hard to take a shot with my tool in one hand and the camera in the other.

The plan is to warm up the crack a bit with the heat gun, to give a little more working time with the hot hide glue.

Then I'll hold the crack open with the spatula, get hot hide glue into the joint, then clamp it up.

Good luck to me.

We brush hot hide glue into the joint.

This is actually a little staged - I did use the spatula to hold the crack open more.  I just couldn't get a picture off while holding both the brush and the tool.

But you get the idea.

You have 60-90 seconds to get the glue in and the repair clamped up before the glue begins to gel.  Have to work quickly.  I always do a dry run or two to make sure everything's read to go before I use glue.

All clamped up.  You can see the new caul on the top.  There's also a flat rectangular caul on the bottom - note the waxed (aka paraffin) paper on the caul in case glue gets on it.  Don't want to glue the caul to the mandolin!

I was able to get the crack mostly closed.  It's a wide crack, it's been sitting for decades, and there isn't much movement overall.  We do what we can.

Here's the finished repair.  It's solid, but as you can see, there is still a bit of open crack.  Not worth losing sleep over...the main thing is that it's not going to move any more.

Note the green arrow - I inadvertently took a chip of wood out with a spatula.  Dagnabbit!

I suppose I could fill it with sawdust, but to be honest, compared with that old patch repair above it, it's not that bad looking.  I can always go back and finish it.

So we now have a stable, repaired crack.  Guess what?  I found another crack on the top that needs to be repaired!  Onward.