Priming over original paint
 

Not wanting to have to sandblast, strip or sand the original paint on the roof of my 70 suburban. This is what the paint looks like when sanding with 180 grit sandpaper. It is getting what looks like a pitting effect in the primer. Any thoughts on what I should do?

Paul

Re: Priming over original paint
 

just guessing, but it looks like the primer was really ruff under the paint and when you sanded it you took the paint off the high spots of the primer....
im sure the paint gurus will step in and answer better than me ,but id sand the paint/primer off and start with clean metal

Re: Priming over original paint
 

The top left area in the second picture looks good. No more sanding required there. No need to remove all the paint to bare steel unless it's falling off. The little spots look like it is falling off so more sanding is required in those areas.

You want a "tightly adhered surface" to apply primer to.

Re: Priming over original paint
 

Looking at left picture, the small spots in the grey ?? through to the red oxide appear to be delamination in those spots. Looking toward the lower left corner of the same picture, you appear to have the same delamination spots from the red oxide to the bare steel. How do you know when the issue will stop? I would err on the side of caution here, much easier and cheaper to strip to bare metal now than after your fresh paint starts delaminating as well.

Re: Priming over original paint
 

In the first picture the white area is where there is a low spot in the metal. It is the original white paint on the roof (this truck was gold with a white painted top). The area just below that spot is where I sanded through the white and the gold paint. The roof paint is nice and smooth but where I sand it the gold seems to flake off in tiny spots. The spots circled in red below show where the gold is flaking off leaving pits.

Looks like I'm going to have to sand down the entire roof down to bare metal. That's going to have to wait for better weather. We got 22 inches of snow earlier this week in NJ.

Thanks for the responses guys!

Paul

Re: Priming over original paint
 

It looks to me like you'll have to sand the whole roof. You can leave the white paint (low area) alone if you like.

It's not important to strip every panel of all coatings when painting but in this case, I'd agree that the previous coating has failed, and therefore must be removed.