Well...
My brother has schooled/scolded me many a time about being too timid with surface prep. Claiming I take too long. With him being an autobody journeyman he disassembles, cuts, welds, reassembles, sands, primers, sands, primers, sands, colors, clears, wet sands, and polishes a whole front end in the time that I would still be sanding. LOL!
His first gripe was that I was sanding with too smooth of sandpaper. He said use 80 grit and he was right. 80 grit would rip the paint right off. I would say a Sport 40 would take approximately an hour to sand all the paint off.
Then he suggest that I prime with FeatherEdge Primer.
Keep in mind that for Autobody Specialist it's all about speed. The more cars they can whip out the more they make. They can't sit around waiting for paint to dry. LOL!
The FeatherEdge Primer is a Catalyzed primer with outstanding fill properties. It's catalyzation also allows you to control how fast you want it to dry with the amount of catalyst you put in it. It can dry so you can sand in an hour. And it sands easily with it quickly turning to powder.
I dry sand using a special powder treated sandpaper. I think it's 180 grit. It's not marked so I forget. The powder in the sand paper helps keep the sand paper from clogging. I can sand a primered boat smooth within the next hour. However, it most likely will take another coat to sand fill and sand out the deep scratches 80 grit leaves so that's another hour to prime and let dry then sand again.
But in about 4 hours I have strip sanded the boat, primed and sanded it twice making it ready for for color coating.
Using automotive paint I can color coat. Wait an hour, (hour 5), Mask and paint again (hour 6) let flash 15 to 30 minutes. Add Decals and Clear Coat. (Hour 7 and 8). In one day if I want to hustle through it I can strip, prime, sand, prime, sand, color, mask, color, decal and clear in an 8 hour period. It's a lot of work in one day and you are surely tired But I did it. I painted two boats for my dad over the fathers day weekend last year using this method. I have attached the results here.
Before....bmp
After2.bmp