Recent Finish Problem

[Budha]

I have a finish problem that showed up since yesterday morning. I will post pictures for you to see. I changed the strings on my mandolin yesterday. I am fairly new to changing mandolin strings but I have been changing strings on banjos and guitars for many years without a problem. I used a MusicNomad neck rest. The same neck rest I have used for several years for string changes on banjos and guitars. I don't know what else may have caused this finish issue. The nitro is still there but the color is faded. The finish does not feel raised or cracked. I was wondering if anyone has seen anything like this before. I am guessing the neck rubbed against the neck rest while I was winding the strings on but I am not sure. Any thoughts are welcome. It a Northfield NFS-F5.

Thank you

Bud

[MontanaMatt]

Try another pic attempt, it’s not in focus enough to see clearly.
Have you tried rubbing with a clean rag? Could it be a residue or deposition?

[rcc56]

Some lacquer finishes react with plastics and various other polymers.

In the 1990's and early 2000's, new Gibsons would react to the cushioning on some brands of guitar stands. This drove the dealers nuts when they found out the hard way. I don't know whether the problem still exists.

At any rate, for this and other reasons, I make my neck rests myself out of wood, and cushion the bearing surface with a piece of old leather.
I use old leather, because I have found that some new leather straps will also react with finishes. Perhaps it's the dyes that are being used.
Often, I'll also throw an old towel or wash cloth over the bearing surface, especially when I do fret work. That way, the leather won't pick up metal fragments left from the filing processes.

Find a piece of plywood, a piece of 5/4 one inch board or 2 x 6, and an old worn out leather belt, saw an arc out of the 1 x or 2 x, blunt the edges, screw it to the plywood base, glue on the leather, and you're in business.

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A skilled craftsman might be able to touch the spot with a brush dipped in lacquer thinner and blotted pretty dry before touching the spot.

Warning: Touching it up is a job for a pro. The technique is risky even for someone who knows what they're doing, and a recipe for disaster for a do-it-yourselfer. If the brush is too wet, it will cause a much bigger problem than what you started with. Ditto if you don't let things dry thoroughly before letting the spot touch anything else. And it must not be polished for at least 5 to 7 days. 2 weeks is better.

[sunburst]

Yes, a better picture is in order here... but...
You mentioned lacquer, do you know the finish is nitrocellulose lacquer? (not varnish, catalyzed varnish/lacquer, waterborne, UV cure or some other of the myriad of finish options currently available)
If so, it looks suspiciously like an adhesion problem and unfortunately yes, I have 'seen anything like it'. I am currently refinishing a guitar neck because of adhesion problems. Lacquer is just not the same as it used to be. The finish makers are loosing suppliers and having to switch, resins and chemicals may or may not be the same, it is looking like a dark time for finishers. The same procedures that worked great for 30 years are giving problems.

[Budha]

Thank you your input. I have tried rubbing with a clean rag and cleaning with water. Northfield's spec says the finish is Nitrocellulose Lacquer. I have attached another picture. I hope this is a better picture for you to examine.

[Budha]

I think the idea of the nitro lacquer reacting with the material of the MusicNomad neck rest is likely the cause of the problem. I learned my lesson. I will take the advice and build a safe neck rest.

[David Lewis]

You might try a micro fibre cloth in the part you lay the neck in, so you can keep your rest and protect your finish?

[rcc56]

I agree with John-- it looks a lot like an adhesion problem.

Time consuming to fix. It might or might not be possible to drop-fill it. The repair would be visible. The finish might come loose in other spots. If so, a larger area would have to be refinished, and the repair would still be visible.

You might be better off leaving it alone, and living with the wear-and-tear.

[Budha]

I agree with John-- it looks a lot like an adhesion problem.

Time consuming to fix. It might or might not be possible to drop-fill it. The repair would be visible. The finish might come loose in other spots. If so, a larger area would have to be refinished, and the repair would still be visible.

You might be better off leaving it alone, and living with the wear-and-tear.

I do plan to leave it alone. I just wanted to understand the cause so I don't do more damage in the future. Thank you for sharing your thoughts.

[pheffernan]

How high can a speedneck go?

[rcc56]

If it is "loose finish," using the neck rest may or may not have induced a chemical reaction that contributed to the problem; but after seeing the clearer picture, I think that's rather unlikely. It's more likely that mechanical action against the neck rest could have hastened the finish's letting go. Or the damage could have been inevitable just from handling the instrument.

If it isn't due to a chemical reaction, the real problem is that the finish isn't gripping the wood strongly enough; and any mechanical action or even expansion and contraction from weather changes will cause it to let go. There's not much you can do to avoid that.

We see the same thing from time to time on some modern era Martin guitars. IIRC, it is most common on their instruments made in the 1990s and early 2000s.

[CES]

If it’s new and under warranty it may be worthwhile to reach out to Northfield. I wouldn’t send a mandolin back for those small changes, especially if I thought I caused it, but, if it starts to get widespread they may be willing to help you out. I’ve got a National RM-1 that’s doing something similar and it just sat in its case for a few months while I was playing others. In my case I think it’s an adhesion problem as rcc56 suggests, as there’s nothing in the case to “off gas.” I guess theoretically it could be a glue issue, but not likely. I’ve had the thing for well over 10 years now, and it’s just mojo.

[HoGo]

I've solved similar "blisters" under finish by pricking a tiny hole (or couple depending on area) with tip of very sharp scalpel and application of drop of diluted shellac (1 pound cut or thinner) and if needed pressing the blister against the wood with finger using non-stick plastic sheet (polyethylene or such).
Of course this blistering may be just start of larger adhesion problem and new ones may start appearing soon. You may contact Notrhfiels about the issue, they may have already tried fix for you.
O my kids' super cheap ($5) "campfire" guitar where the blisters started cracking and flaking away exposing soundhole ring decal I managed to save it by flooding of thin CA and massaging it into all voids with finger (through plastic foil that won't stick to CA). I painted few missing pieces of decal with sharpies and then filled with more CA. Once I polished the top the result was surprisingly good.

[Nick Gellie]

Sorry to hear this happening to you. I stay clear of lacquer finishes. I use various shellac derivatives in my finishes for mandolin and special violin varnishes based on original Cremona style recipes. As they didn't have access to such modern finish compounds they end up easier to apply and easier to fix.