Today I am continuing the finishing of two guitars, a grand auditorium w/ Florentine cutaway and a tele style electric. At this point I have put on several coats over the course of a few days. Each day before I start a new round of spray applications I level sand w/ 400 grit sandpaper. Level sanding removes a fair amount of finish, so it takes several days to build up enough coat to make sure I don't sand through the finish during final wet sanding and buffing. The trick is to make sure you don't sand through, but not make the finish too thick. It comes with experience.
I have constructed a spray booth using dense foam insulation. The wings are hinged so it can be collapsed and stored easily. A simple 20"X20" box fan is placed behind the booth w/ a 20"X20" opening that accommodates a furnace filter to capture overspray. The window behind the booth is open to the outside. I don't need an explosion proof fan because I am using water based finish.
My finish is Target Coatings EM 6000. I have been very pleased with this finish and after a few guitars I have become accustom to it's characteristics. It has excellent properties that are conducive to application and the end result is a pleasing nitro-like appearance. I use a Fuji Q3 HVLP (High Volume Low Pressure) spray system. The spray gun is retrofitted to accept a smaller finish reservoir which is more conducive to guitar finishing.