Crack on Top

[Kevin Briggs]

Whelp....

I got a mandolin Friday and then dropped it on my hardwood floors Saturday morning....

It now has a two inch crack on the top (Engleman Spruce) that does not appear to go all the way through. It runs from rounded end of the f-hole to teh front of the top, near where the fretboard meets the body. It is a very thin, hairline crack that does not seem to impact the tone.

Thoughts on repairs?

[sunburst]

Probably superglue, especially if the finish is lacquer.
It's a special procedure using striping tape or some other tape that seals against superglue. Tape very accurately each side of the crack, apply thin CA, it soaks into the crack, let it partially cure, fill the void between the two tapes, let cure completely, scrape the ca level with the tape, sand the CA down into the tape, remove the tape, level sand and buff. When done well, the crack and the finish are both repaired and the repair is invisible (if it was a tight, clean crack). If the finish is varnish or if the final finish is less than high gloss ("satin"), this will not work.
Another method is to try to force as much hot hide glue into the crack as possible using clean fingertips. That can repair the crack, but it does nothing for the finish.

[Kevin Briggs]

Probably superglue, especially if the finish is lacquer.
It's a special procedure using striping tape or some other tape that seals against superglue. Tape very accurately each side of the crack, apply thin CA, it soaks into the crack, let it partially cure, fill the void between the two tapes, let cure completely, scrape the ca level with the tape, sand the CA down into the tape, remove the tape, level sand and buff. When done well, the crack and the finish are both repaired and the repair is invisible (if it was a tight, clean crack). If the finish is varnish or if the final finish is less than high gloss ("satin"), this will not work.
Another method is to try to force as much hot hide glue into the crack as possible using clean fingertips. That can repair the crack, but it does nothing for the finish.

Thanks, John!

What's CA?

[HonketyHank]

CA=cyano-acrylate=superglue

[John Kelly]

It's the chemical name for Superglue - CyanoAcrylate.

[Kevin Briggs]

It's the chemical name for Superglue - CyanoAcrylate.

Thanks!

Know where I can get striping tape?

[sunburst]

I get striping tape at auto paint stores. High quality electrical tape can work, but there is usually more clean-up involved after it's use.

[Bill McCall]

If you need to ask about CA and tape, you might also need to ask 'where can I find a qualified repairman?' assuming this is a reasonably valuable mandolin.

But don't let me spoil your fun learning.

[Dave Sheets]

This isn't a hard job for a good repair-person, so that means it won't be a horribly expensive repair, but some experience does make a big difference in how good the repair looks. If this is a relatively expensive mandolin, it's worth getting an estimate if there is a luthier or repair-person in town. If it's a less expensive instrument, and you are comfortable, the DIY approach is likely to be fine.

[mirwa]

Personally I would work some titebond into the "suspect crack" or some fish glue / hide glue.

Super glue is good for doing touch up finish repairs, I just do not like it for crack repairs.

In my signature line is a link to some tutorials which may get you started and feel more confident.

Steve

[Kevin Briggs]

Personally I would work some titebond into the "suspect crack" or some fish glue / hide glue.

Super glue is good for doing touch up finish repairs, I just do not like it for crack repairs.

In my signature line is a link to some tutorials which may get you started and feel more confident.

Steve

Thanks! I got the glue in, and the crack is stable!

Now, I need to sand it down and smooth it a bit. Any tips?

[mirwa]

Yep, go slowly.

I always do my sanding with a backing block, it stops you from creating divots.

Steve

[Kevin Briggs]

Yep, go slowly.

I always do my sanding with a backing block, it stops you from creating divots.

Steve

Thanks, Steve!

What gauge sandpaper should I use for a satin finish? Or, should I just worry about getting it nice and sanded first and then worry about the finish later?

Thanks!
~ Kevin

[William Smith]

Probably superglue, especially if the finish is lacquer.
It's a special procedure using striping tape or some other tape that seals against superglue. Tape very accurately each side of the crack, apply thin CA, it soaks into the crack, let it partially cure, fill the void between the two tapes, let cure completely, scrape the ca level with the tape, sand the CA down into the tape, remove the tape, level sand and buff. When done well, the crack and the finish are both repaired and the repair is invisible (if it was a tight, clean crack). If the finish is varnish or if the final finish is less than high gloss ("satin"), this will not work.
Another method is to try to force as much hot hide glue into the crack as possible using clean fingertips. That can repair the crack, but it does nothing for the finish.

Yep I've used super glue also on an old A-50 that was beat up, took back off regraduated it and used glue for small top cracks and to my knowledge it still sealed to the day..

[mirwa]

To achieve a satin finish, simply wet sand with 1500 grit, that does a nice job.

Provided you have aligned everything properly and there is sufficient thickness to the area of concern then yes flat sand until smooth to the touch using 220 grit and a backing block, then follow up with 400 and lacquer

Steve