Finish damage question for the Builders here

Last Tuesday I received a custom OM I commissioned from a builder in British Columbia, Canada. I live in central Florida.

The guitar was shipped but quarantined by the freight forwarder at the US port of entry and held there for a couple days. Unbeknownst to the builder, on 12-6-2010, a declaration under the Lacey Act was enacted requiring all wood products entering the US to be identified by species and origin on a particular affidavit form. In other words, the builder had to attest that the wood species on this guitar was not of a protected species and legally acquired. This particular OM is Engelman over Honduran mahogany B&S.

Once released, the guitar showed up in the delivery truck about 6 days later. I asked the driver how long the box was in his truck. He said all day. That day was a constant 70 degrees. It was a 4:00 pm drop-off. I waited till 7:00 pm to open the undamaged box. It was a Martin guitar shipping box, appropriately packaged for the journey, and the case of the guitar showed no signs of rubbing or point of impact. (I'm an FAA certificated aircraft mechanic inspector and routinely scrutinized shipments received for obvious and hidden signs of damage). At 7:00 pm I opened the guitar case and found that the finish on the top was cracked grain-wise across the top and in various places equi-distant from each other. In other words, there was nothing in the nature and spacing of the finish cracks that might indicate a localized pressure or impact point. Only the finish on the top was cracked. The Martin shipping box did not appear to have been opened (original taping by the builder was intact) during transit.

How did this finish get cracked? Storage in a extreme low temperature environment? Just curious. BTW, it sounds and plays great and the finish mystery is more a curiosity than an issue with me.

[nacluth]

Pictures would probably be the best way to determine what's going on or if there would be any need for any repair. It's possible that the finish is just thin and has contracted enough naturally it appears as "cracks." At least, if they are more or less equidistant and somewhat regular. But, otherwise temperature variations could cause the lacquer to crack.

My advice though, is if it sounds great and is not too aesthetically displeasing, no real harm done. Enjoy your new guitar.

[Bruce Sexauer]

I would replace the word "thin" with the word "thick" in the previous post, and otherwise agree.

Well, it isn't completely unsightly as it might be because the top is very light colored and it requires a certain angle to see the light refraction in the cracks. It's no big deal to me. The guitar is a keeper but otherwise hardly something to hawk the builder with in it's current state. Some folks get bent out of shape over this kind of thing and I've already had some of them point fingers at him. Silly, sad but you'll have that.

[Tim McKnight]

Do you know what finish is on the guitar? I would suspect that it is nitrocellulose lacquer. It seems to be the most prone to "cold checking" especially if it was applied on the thick side, as Bruce mentioned. Lacquer cracks from a sudden & rapid [change] in temperature. It can handle temperature changes over a S-L-O-W period. However, it "checks" or cracks when a rapid change of temperature is forced. The good news, if it is lacquer, it can be repaired.

[gitnoob]

Originally Posted by Tim McKnight

It can handle temperature changes over a S-L-O-W period.

I've always been curious if anybody has demonstrated this. Seems to me that the magnitude of temperature change would be more important than the rate, assuming that the two materials (finish and wood) contract by different amounts.

[Tim McKnight]

I have some spruce test panels that I sprayed with various finishes. After they were cured, for several weeks, I placed them out doors in winter temperatures in the teens. I then brought them indoors to a room of 72*F and the lacquer panels consistently cold checked after a few minutes exposure to the warm air.

[gitnoob]

Thanks, Tim. You've done some great experiments!

[Tim McKnight]

I should also mention that any lacquer under 6 coats did not cold check but in excess of 6 coats did. This also reinforces what Bruce mentioned above. I also tested 2 French Polish applied Shellac, 4 short oil Varnishes, KTM9, Catalyzed Urethane and Catalyzed Polyester finishes and none of those finishes cold checked above 6 coats.

[terken]

Two things that could be an issue is method of shipment and seasoning of the top wood. I've always worried about rapid changes of temp and humidity with air shipping. The box goes from a facility to a truck, back to a airport facility, then outside and into a plane etc. etc. Lots of fairly quick changes and it gets handled a lot. Also if a top was cut just a few years ago it may be dry but not really seasoned and could move more with rapid temp and humidity changes.
The only nitro top I had check was an overnight air shipment in the winter with temps in the 20's. It was fairly recently cut Lutz that I had not baked. I've never had a winter ground shipment problem so far.
Any thoughts?

[Brackett Instruments]

A picture might yield some more guesses about your problem. Does it look like the pictures in this thread on the OLF?

[nacluth]

So what I was describing earlier is what I have heard reffered to as "reeding." What I would call a telescoping of the grain structure through the finish. I personally like the look and it happens with the cat U that we put on our guitars.

Is this something that typically happens with thicker finishes over thin ones? I say this because I thought our finishes were thin to average, definitely not as thick as factory finishes, or were the "thick" comments directed towards actual cracks?