Crawls Backward (When Alarmed)

IconProjects, musings about guitar builds, guitar repairs, vintage tube amplifiers, old radios, travel, home renovation, and other stuff.

Crack Repair on Top of 1919 Gibson A-4 Mandolin

When I worked on the side crack on the Gibson mandolin, at some point I noticed this crack in the top.  I just didn't pay much attention at first, until I realized it was the center seam and it was a crack that needed attention.

I'm actually holding it open a bit in this picture.  It wasn't quite that bad looking and open in reality (maybe that's why I sort of missed it even though it was plainly visible...).

Anyway, I set about fixing it.  Top cracks are generally the most straightforward body repairs on an acoustic instrument, since they're the most accessible.

The process is: hold the crack open, work some hot hide glue into it, then gently but firmly clamp it down to close it as much as possible.  This crack closed up nicely with some pressure in a couple spots along its length.

I discovered my cam clamps were too big to get into the soundhole, so I improvised with this cast iron c-clamp.  I just stuck some cork on the bottom with rubber bands so it wouldn't damage the inside bracing of the mandolin.

Here's a simulation/test of the actual glue application.  Heat the surface up a bit with a heat gun to help give the glue a longer working time.

Then I reached in from the end pin hole with some long tweezers with an angled end and pushed up on the top.  Then brush some hide glue on, while working the crack up and down gently.

And repeat from the soundhole end - with fingers inside the mandolin.

What you see above is just a test with some glue.  I wiped that off with a warm, damp cloth before the actual operation.  When I did the actual repair, I was able to get the crack nicely opened up and glue worked into the seam.

One of the things I really like about hide glue is that it's so easy to get excess off, even if it dries.  In this instance, I put a pretty liberal amount on, then wiped the excess off quickly before I clamped it up.

Work the glue into the crack, then quickly clamp it up.  I used a couple pieces of thin plexiglass as cauls.  They're strong enough to hold the crack down, and you can see your progress through them.  With the clamps on, the crack closed right up.

I won't bother cleating this from the inside.  The crack will be pretty tightly closed up, and the hide glue tends to pull the crack together as it dries, making for a strong repair.

I only cleat when absolutely necessary - meaning when a joint needs support.  This crack will be solid.

Here's the seam after repair.  I still need to clean up a little glue squeeze-out, but it looks good.   And it's much less noticeable in person.

My guess is the seam has been open for quite some time, so I'm happy with the way it closed back up.

Love that sunburst!  Much more subtle and natural than Gibson's 1950s sunbursts, I think.


Post a Comment 0 comments:

Post a Comment