Can I apply body filler to sanded paint? Or can I only apply to bare metal?

[icapture]

Hey guys. So Ive welded up all the holes and now its time to start smoothing out the body and prep it for paint. Now I know there is a right way and a...not so right way to prep a car for paint. The right way is to sand it down to bare metal, prime, and paint. But my car has about 4 coats of paint on it already and although I could strip all the paint off I've decided that I don't want to invest that kind of time into the Z and have the car off the road for that long. Instead I would rather just rough up the entire car, apply body filler where needed, and give the car a single stage paint job (white.)

 

My driver side door has a good size patch of bondo that I found when i was sanding the rivet holes along the side of the car. I started exploring with my sander to find where the bondo ends. So as you can see in the picture there are many little indentations. My question is can I apply bondo to just these spots? Or does the entire door have to be sanded to the metal, then apply bondo?

 

[junglist]

Prime before you apply the body filler to help with better moisture resistance.

[pat1]

Depends on the filler. Read the directions on the filler. Some filler will peel right off paint.

[yetterben]

I would use a skim coat of glaze.

[280zjoel]

Try this stuff, it works great on paint:

http://www.autobodytoolmart.com/3m-piranha-advanced-finishing-putty-05821-p-10961.aspx

[greghassen]

When I worked in an auto body shop we used to apply bondo over paint when it was determined that the paint

was in good condition... i.e. not peeling or flaking. Back then lacquer putty was king and would shrink

later and make the body work look wavy so we preferred using bondo in place of spot putty. This is not to

say that bondo doesn't shrink, but it shrinks less..

 

For surface prep you will have to rough up the paint before you apply bondo. I've used 36 grit if the paint is

thick, but if not thick, you can use 80 grit. The bondo needs this to bite into the paint. You shouldn't apply the bondo over paint very thick though.