How to fix a top crack?

[buckwild]

I am working on my second A style mandolin.
I finished carving the top and noticed two hairline cracks on the bottom. If you picture where the tailpiece goes, they are on both sides of it. I was wondering if anyone can recommend how to repair this before i cut the f-holes and glue the tone bars. Is it better to use super glue, epoxy, etc....
Thanks!

[sunburst]

New top, not glued on yet?
Probably superglue, or hide glue.
Epoxy might work too, but I don't think there's any need for it.

I have, and I know of many others who have glued tight cracks with superglue and they've held up fine. I've also glued them with hide glue, but it doesn't wick into the crack the same.
With water thin superglue, all you have to do is touch a drop of glue to the end of the crack and it will wick in and fill the crack.

[Stephanie Reiser]

has anyone closed and glued a top-crack between the bridge and tailpiece about the thickness of a pick, with the top on? I have one in the shop now, but want to get around removing the top.
Thanks

[sunburst]

Stephanie, that usually happens because of the top being too thin in that area. The tail block rotates from string tension, and the top isn't rigid enough to keep that from happening, so it bulges up. The bulge pulls the center seam apart, or opens a crack.

It's hard to repair. I've seen a bunch of them glued only to open back up. One of the few successful (so far) attempts that I know of, is in Roland White's Randy Wood mando. The repair is basically a "wall papering" of the inside or the top with cloth and glue for a reinforcement against the crack opening again. I don't know if you can do that without taking the top off.

[Chris Burt]

I've a narrow, tapered scraper that I draw through such cracks to:
- taper the crack so that it's wider on the outside of the arching and narrower on the inside.
- equalize the width of the crack.
Remove as -little- wood as possible and leave the crack the shape of a long thin football.

Plane a long, thin splint of wood to fit the crack. Use wood with similar grain run-out characteristics. Use Automotive striping tape to mask either side of the crack and mask off the rest of the top as necessary. [Thanks to those who recommended this tape, it is, indeed, great. Expensive, but worth it.] Glue splint into crack. Surface splint down to the rest of the top. Seal splint with clear shellac. Use dry brush technique to match the color of the splint wood to the rest of the top. Remask crack and french polish the splint and very narrow area either side of the splint--the tape protecting the rest of the top. Remove tape. Taper edges of french polished finish with micro mesh. Hand rub to blend.

[Frank Ford]

Amanda Lyn -

Of course you should try to glue the crack without taking the back off! IF you glue it and it doesn't hold you can always do something more invasive later if you have to.

Back in my salad days, I hung my newly completed mandolin up high in the living room, not far from a wall heater. Next day, I heard a loud CRACK as the top split wide open down the middle. That was in 1970, and I repaired the crack by mashing in some hide glue (I used packaged liquid hide in those days) and clamped the crack closed by sticking a pair of cam clamps over the entire instrument. I did no reinforcement inside.

The repair has held perfectly all these years, and the top is still intact. I've done this repair on lots of instruments since, mostly with success. I do agree that if the top is too thin, this may not be a successful repair.

[Chris Burt]

Addendum: The splint technique only works if the crack is wide enough to make a splint for. Don't widen the crack just to put in a splint. Also, don't forget to take humidity into account. If it's dry in your shop and damp in the environment the mando will live in...

[Stephanie Reiser]

Also, don't forget to take humidity into account. If it's dry in your shop and damp in the environment the mando will live in...

Yeah, the owner uses a woodstove for primary heat. That is brutal on instruments.
Thanks everyone.

[PaulD]

Yeah, the owner uses a woodstove for primary heat. That is brutal on instruments.

Suggest he or she keep a pot of water on top of the stove... makes a pretty good humidifier if the building is tight enough to retain it. The only place I've lived with only a woodstove for heat was so drafty that a good winter wind would blow papers off the kitchen table. We also could have fattened up nicely on all the voles (like big, round mice with long tails) that we'd catch coming up through the floor from the crawlspace... if frying up voles didn't sound so repulsing!

pd

[Chris Burt]

Yet another addendum: The tapered-splint technique I mentioned works for flat-topped instruments. For a carved top, you'd have to use a splint (and a prepared crack) with parallel sides, a more difficult fitting process, but not impossible.

[PaulD]

Yet another addendum: The tapered-splint technique I mentioned works for flat-topped instruments. For a carved top, you'd have to use a splint (and a prepared crack) with parallel sides, a more difficult fitting process, but not impossible.

Chris; why doesn't the tapered splint work on a carved topped instrument?

Paul Doubek

[Chris Burt]

The splint has to be cut from slightly oversize veneer of early wood to match the shape of the arching, and then thinned to fit to crack. Imagine the crack is not straight, but curved, which is most likely. With a crack that varies in location though three variables (x, y, & z), adding a taper to the splint adds more complexity. I'm not saying it can't be done, but fitting a thin splint to three variables is hard enough. Admittedly, one variable is partially taken care of by bending the splint to fit the wander of the crack, but the difficulty it presents still exists.