In the first case, let me say that it is exceedingly rare for a car to “just need a re-spray”. To get away with this, the car must have no rust poking its ugly little head out of cracks, corners or seams. The existing paint must be in good shape, with no splits, checks, shrinking, peeling or mysterious behavior that might come back to bite us. Perhaps the car was kept garaged and regularly polished, so that the paint is wearing thin. If we can crawl all over the car, and we decide that an additional layer of paint will survive on top of the existing work, we can rejoice.
A final caveat at this point: I don’t like shooting modern paint over lacquer. A car painted in lacquer, like in the “good ‘ol days” can be a thing of beauty. However, lacquer is not a long-term paint job. It is never “done”. It is always absorbing chemistry from the air while out-gassing others, and it is the least durable of any paint in direct sunshine. Its advantage lay in being cheap and simple to apply. When man-hours were not worth much, anyone could keep laying on coats of lacquer until the stuff was thick enough to cover a housefly. Then he’d just polish it until it gleamed. Ta-daa! Shiny paint! Never mind that it would check and fade and go chalky in a couple of years. It was cheap enough to do again. Anyway, back to our re-spray.
The first thing we need to do is what I call “field striping” the car: we pull the trim, chrome, glass, lights, doorseals, and anything that will keep us from applying the paint in as close to assembly-line condition as we can. We carefully mask off the interior and drape the engine, to keep dust or splashing from rinse water out during out prep-work.
Assuming that we are content with the shape of the car, and do not have any dings, bends or flaws to repair, all that we have to do is wet-sand the car to a minimum of 400-grit, 600-grit is better. The car is rinsed clean. Then the entire car is wet-scrubbed with a gray scotch-brite pad dipped in Ting, which will remove any sanding grit or oils and leave the car clean enough to sheet water. The used masking can now be pulled off.
The car is moved into the paint booth and wiped down with lint-free towels. The car is positioned where it will be painted, on stands if required. It is re-masked with fresh masking paper. If the doorjambs are not being painted, the doorgaps will get masked off with an adhesive-backed foam rope that will allow a soft paint break between the old jambs and the new paint on the outside.
The entire car gets wiped down with a grease, silicone and wax remover to eliminate fisheyes and contaminants. Finally, the car gets wiped over with a tack rag to remove any dust specs that may have wandered in during the preceding work.
Now we can get down to that magical “about three hours” that I mentioned: the actual process of painting the car. The first application will be an epoxy primer, with added reducer that will act as a sealer to lock down the previous paint and to promote adhesion of the new. This needs to dry for at least an hour.
Now is the last chance to inspect the car for any flaws, fisheyes, or dust inclusions. If there are any problems, they need to be fixed now with a bit of wet-sanding. Any touch-ups that break through the sealer get the whole clean treatment again and get re-shot with the epoxy primer sealer.
Now comes the paint. I generally plan on color-sanding and buffing the paint, so I want an extra full coat to a coat-and-a-half to play with. In order to leave at least a 4 mil. paint thickness after buffing, we are looking at 4 full-wet coats of single-stage enamel. I know how much primer it took to seal the car, so I know I need 4 times that much shootable paint. The paint gets mixed all at once, and it is ready to keep my gun topped up as I go through the process. It takes only about 10 minutes to shoot a coat of paint, including the time spent moving stools, checking the air hose and moving around the car.
After shooting a coat, I load up the gun for the next coat and dash out of the booth for a breather and a sip of water. I check the clock and go back into the booth about 10-15 minutes after I stopped shooting the previous coat, depending on temperature and humidity. Starting at the same place each time, I repeat this dance 3 times.
Keeping paint gun motion steady and even, while keeping the proper distance from the work, controlling paint flow while watching the wet line as I go, and still keeping an eye on the upcoming panels, is quite a lot to do at one time. It looks quite a lot like some slow motion dance: me crab-walking around the car, with my arms gesturing in an arcane ritual to sommon the Shiny-Paint Gods. I jokingly call it Paint-Chi. It certainly is a workout.