How to remove the Existing paint?
We've found that stripping entire panels using a sand blaster is too messy and can easily damage the metal while chemical stripping is also messy and difficult to clean properly after stripping. Plastic media blasting is best but needs to be done using expensive equipment so it's usually farmed out and expensive.
Several years ago we discovered we could strip a car quickly and inexpensively using a good variable speed sander/polisher and good hook and loop sanding disks. We tried stick-on disks and inexpensive sandpaper but found it to be much less work and much less sanding when high quality hook and loop paper was used. We can now strip about 90% of a car using this method in about 8 to 12 hours under normal conditions. The other 10% of the paint is usually removed using a smaller sander, a small blaster or chemicals.
The sander can quickly remove several layers of material as long as it can rotate slowly (usually 1000 RPM or less) so that it doesn't heat the paint or metal.
(Click to Enlarge)
Above the car is shown with the fender and both doors stripped. Notice that the bumper is masked with several layers of masking tape to protect it from being damaged during the stripping process.
We've found that 80 grit disks work best for most stripping processes because it leaves a scratch that allows the primer to bite the surface well while still easy to fill with most epoxy or filler-type primers.