Help Identifying an Issue

[Em Tee]

I know y'all likely won't be able to diagnose this via a photo, but there's no luthiers in my area so I thought I'd give this a try.

Is this a crack in the paint or the seam of the wood? And if it's a crack in the seam, what should I do?

(Having some technical difficulties on mobile site, photo to come)

[Em Tee]

[Greg Mirken]

Nobody can tell definitively from a photo. You can take some mild solvent like naphtha or mineral spirits and rub it into the area. Either will evaporate harmlessly and have no effect on the wood or finish. If you can see a wet spot inside, it's a seam separation. If not, it's just that the wood has moved with environment change and the lacquer has checked along the seam. It happens.

[HoGo]

Nobody can tell definitively from a photo. You can take some mild solvent like naphtha or mineral spirits and rub it into the area. Either will evaporate harmlessly and have no effect on the wood or finish. If you can see a wet spot inside, it's a seam separation. If not, it's just that the wood has moved with environment change and the lacquer has checked along the seam. It happens.

I'd say it is partial seam separation, this happens when humidity drops suddenly way too low. The seam inside may still be perfectly closed and glued to the block. I had exactly this happen on one of my early mandolins. I was fighting with humidity swings in my workshop because some leaking water plumbing in neighboring rooms so I bought dehumidifier and turned it on but without proper control it lowered humidity from 60% down to 30% or even lower overnight and the mandolin I was just french polishing ened with esxactly same separation.... I fixed it by massaging in some thinned HHG and then after the humidity was stabilized at 45% it remained stable and almost invisible.
If your mandoln has HHG joints you can try it as well (after inspection with magnifying glass). Try to keep the area clean not to contaminate the gap inside (if present).

[Folkmusician.com]

Can you shine a light inside and check the seam there as well. It looks like it is far enough past the block to tell.

[Em Tee]

I live in South Florida. This mandolin has been in florida for about 4 years now. I don't think any major changes in the constant swamp levels of humidity have happened recently. (I live in the everglades)

I am very very ignorant to woodworking and luthiery. What is hhg?

[Rich Benson]

hhg - hot hide glue

[Em Tee]

Can you shine a light inside and check the seam there as well. It looks like it is far enough past the block to tell.

As far as I can tell (from my VERY untrained eye) the seam looks okay on the inside.

[fscotte]

Hot hide glue will fill that seam up. Sand with 1000 grit, then 2000 grit, polish with Meguiar's 105, and youll never see it.

[Em Tee]

I fixed it by massaging in some thinned HHG and then after the humidity was stabilized at 45% it remained stable and almost invisible.
If your mandoln has HHG joints you can try it as well (after inspection with magnifying glass). Try to keep the area clean not to contaminate the gap inside (if present).

Do you know of any tutorials or have any reccommendations as to how to thin (do i just use water?) and massage in the hhg?

[HoGo]

Do you know of any tutorials or have any reccommendations as to how to thin (do i just use water?) and massage in the hhg?

This only works if hide glue was used originally. The new glue both melts the old layer and adds new and the humidity from the water inhe glue humidifies the wood around the seam and helps close the gap.
HHG is prepared like edible gelatin (hide glue actually IS less refined gelatin and you can in this case use knox instead of hide glue). You let it soak with cold water (roughly 1:1) for an hour or so and then heat in water bath (to 140degrees F, not more) and mix it. I would add few drops of water at a time till I get it thin enough to use in the pot. Must be used while still hot and best if the environment is warmer and perhas the area of the crack heated somewhat above ambient temp for longer working time of the glue before it cools and becomes gel. I would put few drops on the crack and tap over it with fingers and massage to get best possible penetration (or use syringe with O ring around the tip to force glue in). Then quick wipe with damp towel so no glue dries on surface of finish and damage finish. after that I would repair the cracekd finish (most likely just some shellac) and smooth / polish it.

[Br1ck]

I'd take it or send it to someone who knew what they were doing. You could make it worse and then the guy who knows what he's doing will have a hard job instead of an easy one.

[Greg Mirken]

I don't think you need to get too excited about this. Since you are in an area of pretty high humidity it may be just the opposite of what we have speculated, that higher humidity has caused the joint to swell a little.
What instrument is this? Have you done the naphtha test?

[Dale Ludewig]

I'm only looking at the pictures, of course, but I don't see a gap. And probably half of that seam is over the tail block. From here, it looks like glue cold creep. This is complete speculation but it looks like the center joint could have been glued with Titebond or something like it. The back is glued down real tight to the tail block. So if the wood got hot and humid, it will swell. And that can cause the glue to push up a little at the seam because the wood is so constrained by being glued to the tailblock. A little further away from the tailblock, the back can move "up" to adjust for the swelling and no glue squeeze out. I have a Guild guitar from about 1970 that had that same look running down the center back seam.

[Greg Mirken]

I think Dale and I arrived at the same conclusion...

[Em Tee]

This crack is a week old. The mandolin is almost five years old.