Since I got my 2000 Laguna about 3 months ago I had been washing it by hand (with the Flash system). But the last couple of weeks has been pretty grimy, and I'm loathe to spend too long washing it for it to get rained on again straight away.
As my car was a fleet car it has light swirls on the paint already, so has obviously been through a car wash a fair few times (possibly all the time, I can't see reps bothering to wash by hand that often).
So last week I decided to try it through our bus wash at work (like a big car wash that'll take a double decker bus, or wagon). I used to wash my last car on it all the time and nothing ever happened, although my previous Sierra Estate did get a damaged mirror off it. Anyway, I thought, better to was it regularly on the bus wash to keep the grime and rust at bay, than to was it less often by hand. So it's been through twice over the last week and came out looking fine each time. Just a quick squeegee of the bonnet and windows and left it to dry.
It looks a lot better than covered in grime all the time, and means it gets washed more often so should help to keep rust at bay. Fair enough if you have time to wash it a few times a week by hand, but I don't, and it's parked outside so if it rains, it's as bad as ever after a few miles.
I remember talking to the wash engineer who comes to service ours a few months ago, he does the garage and supermarket ones too. He said if you knew how they looked after them you'd never use them (he was talking about Asda at the time). He said they never change the water (the wash recycles water to use again), so you end up with loads of grit and whatever was on previous cars, on yours. It is filtered by the wash plant, but no doubt a lot gets through, especially if they don't change the water often (even at all).