Overheated Uke

I really screwed up today and left my latest project on my table saw. There is a skylight above the saw. I had 6 coats of lacquer on a walnut uke. The sun shown directly on the back and the little bugger got really hot. Now where the back plates join the lacquer has a line that runs almost the length of the back. It is very very slight and I don't think the joint has in any way failed but what do I do. I'm thinking sanding the back down to bare wood and wicking some CA into the back joint if it has moved at all. Any advice would be welcome.

If all you are seeing is a slight ridge in the lacquer then there shouldn't be any problem. Let the thing dry and cure for a couple of weeks and then level sand it. Then another spray session.

If it's a slight sink back then the same goes. The lacquer getting that hot will have sunk into a hollow that was always there, or the plates have moved just enough with the heat to allow some shrink back to happen.

The long and short of it is that glue gets soft when it's hot. Wood expands and contracts with differences in heat and humidity. When the glue cools it hardens again. Wood stabilises when things settle down. You'll be fine.

You probably have a lees than perfect joint at your seam and the lacquer is the first thing that'l show it. It probably would've showed up in time anyway to some extent, you just accelerated the time line by exposing it to heat. I don't know how thick your finish film is; if it's 5 or 6 mils you might be able to sand flush after waiting a few weeks. I might spray another few coats on top of the seam just to make sure you have adequate thickness. In any event, wait as long as you can before wet sanding and buffing (if you have a problem, it'll show up in the buffing.) A month is not to long to wait.