In all the books I read, and even on the TV shows that show paint prep, the process of panel flattening is always shown to be a hand sanding process with wet paper using an idiot stick or other flat board except on curved areas.
Are DA sanders and inline air sanders not used for panel flattening? I am a bit confused. Don't these tools exist to take out some of the physical drudgery? or they only suitable for roughing in the bondo, but the final flattening must be done w/o air tool help?
Another problem I've encountered--when sanding on a large, flat hood, there is enough flex in the panel itself that I can't feather in the edges of the bondo. It seems that the flexing of the hood allows the sander to brigde over the edge of the repair area. How can I eliminate this problem?
How fine a paper do you use for final prep under a one step top coat?
Thanks
Michael
Bel Air, MD

Questions:
#1 What are you painting?
#2 What condition is it in?
#3 What kind of paint are you using?
#4 What is your skill level with a DA or in line sander?
#5 What's the temperature where you are?

In short there are a number of factors involved in modern painting. You have to almost be a chemist to properly select, mix and apply today's prep and paint. Yes you can block sand with 500 grit wet or dry, but it depends on what you are sanding. Same with a DA if you're applying etch or primer. Modern paints require the matching prep materials or you will waste BIG bucks. If anyone ever wonders why it costs $1500 to paint a car, then they need to go visit a body shop for a day or two.

Thanks Capt'n
I am repainting an '86 F250. I painted it last year and I am unhappy with the results. I was using a friend's garage that lives about 40 minutes away, so it wasn't real convenient. I also felt rushed to get it out of his garage--he didn't apply any pressure, but i still couldn't do as much as I really wanted. I thought the prep was adequte; it wasn't.
I shot a 2 part urethane. The paint is fine--its the poor prep that shows thru.
I "collected: a deer with the right front fender this past Fall. Since I have to repair that, I thought I'd take the opportuninty to redo the whole thing.
As far as temp--Its tooooo cold here ( about 15degrees F right nor) I will wait until I get steady temps in the 60 degree range.

It sounds as if you have some degree of experience but I can't get a mental picture of what you mean by "the paint is fine, it's the poor prep that shows through". This could mean a number of things from oxidation in the metal to sanding scratch swelling. Dupont has a good website with a LOT of info on what prep materials to use with what paint. But like everything else, if you're not trained in a specialty then you're doomed to trial and error. And body refinishing (like electronic engine controls repair) can make for some very expensive lessons.
Any photos of what you have?

Mike,

Not that many years ago an '86 F250 with a deer modification to the front fender would have been an everyday sight in the Bel Air, MD area! I lived there from 1985 thru 2002, Harford County was growing like mad. Seems like things started going "upscale" about 5 years ago. Still a great a place to raise a family though.

Good luck!

__________________
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-Ancient Hindu Proverb
(Are there any modern ones?)

1998 E320 Blk\Blk
1995 BMW 530i (bad engine) sold
1989 BMW 535i sold after 170,000 fun miles
1996 Lincoln Town Car (6 passenger land barge, still smooth and quiet at 130,000 miles, make me an offer!)

Capt'n
Mostly the defects that bug me are the poorly feathered ding repairs. I thought they were well sanded, but it is obvious that i was wrong. Is this hand work only, or can the air powered tools be used?

They can be feathered out with a DA but the final sand must be hand block sanding with graduating grits of wet sandpaper. Prime it and when you cannot detect a surface irregularity when it is wet, then you are ready to paint. There is no more valuable tool in bodywork than a good hand and eye. Now the question, what kind of paint job do you want?? Is it show, go or utility?

This is to be a "utility" paint job. i.e., cover the body so it doesn't rust, but not so rough that it attracts attention.