Up Down or Down Up
I've been conflicted about the best way to wash a vehicle for many years.
When I went to aircraft mechanic's school, they taught us to wash from bottom up. The reason given was that the detergent would trickle down through the dirty part and cause streaking of the lower areas.
When I went through Mequiar's car care course at the Meguiar's training center in Irvine, CA, they taught us to wash from the top down. That was consistent with what Timothy Ma suggests in earlier posts.
What I have concluded is that both institutions have lots of experience but the difference could be the kinds of vehicles we're dealing with. Airplanes are bigger than cars, soyou may tend to take a while to get around to rinsing, and that would give the dripping detergent time to etch the paint. On the other hand, washing from the top to avoid scratching the paint with the grit and road grime is a real possibility. The compromise is to wet down the whole vehicle before starting the wash. Use lots of sudsy water and a sponge (not synthetic, but real ocean sponges) so the grit can float away from the paint surface. I still start from the bottom, and I rinse as I go. Don't let the soap sit and especially on a hot day.
And most important, don't ever buy more scooter, car, airplane, etc., than your (girlfriend/boyfriend) can wax in one afternoon.
