Dripstick: The exact weight of paint would be hard to determine, as some is lost during application. And of course, paint schemes vary widely, from complete coverage to only stripes or logos. From my personal experience, a full coverage paint job on a 747 consumes about 60 gallons of primer with reducer, and 60 gallons of topcoat with reducer. When applied with electrostatic paint equipment, most of the paint goes onto the surface, not into the surrounding air. And one manufacturer's high-solids paint weighs about 10 pounds per gallon. So the weight would be somewhere in the vicinity of 1200 pounds.
When new paint jobs are applied, some operators will remove the old paint, and prime and paint back out from the metal surface. And some operators will only prep the existing paint surface, and apply the new paint over the older paint. Of course, successive layers of paint eventually mean more weight to carry around. As most paint removal chemicals will attack the fiberglass surfaces, the fairings are often just prepared by scuff-sanding, and the new primer and paint applied over the old paint. I've worked on many fairings that had 12 to 15 different layers of primer, anti-static, and topcoat applied during successive paint jobs.
The best technique to find out how much the paint job would weigh would be to weigh the aircraft just prior to the initial paint application, then reweigh the aircraft after the paint job is complete. Boeing has probably done this at least once, and could perhaps supply an accurate figure. And just for your interest, the last full paint job on a 747 I was involved with cost approximately $147,000, for materials and labor. Regards,