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I have been running into some trouble while spray painting my car. The roof of my 2000 Chevy Cavalier Z24 had some rust on it, so I sanded it down, put on primer, and used black Rustoleum for the colour.

I thoroughly sprayed the first coat, and sanded out the bumps with 600 grit sandpaper. I realized I made quite a few sandpaper cuts, so I sprayed another two coats and used 1000 grit paper wet-sand to smooth it out. After this coat, I noticed that the paint had gone a matt-grey colour (from gloss black). I figured I might have pressed too hard with the 1000 grit, and decided to do a final coat and wet-sand with 2000 grit. However, I still got the matt-grey discolouration. Mixed with the matt-grey, there are a few areas that have tiny gloss black spots and lines.

I am using an electric palm sandpaper with 800, 1000, and 2000 grit. The climate is slightly humid, and 22-25 degrees celsius. If anyone can help me out with this, that'd be great!!

  • I think you may be looking at the dulling of the finish caused by sanding. Did it get better after going to the 2000 grit? You might try putting a coat of wax over it (or waiting for somebody who knows more about body work…). – dlu Jul 30 '16 at 5:10
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    It was a lot better after using the 2000 grit, perhaps I am over doing it? – Kevin Smith Jul 30 '16 at 5:12
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    Don't know that you're overdoing it, but just that glossy may be a lot finer than 2000 grit. Try getting it wet with clean water, that should let you see what would happen if you put on a coat of polish or went to even finer stuff. – dlu Jul 30 '16 at 5:15
  • Oh, I see. Yeah, I'll give that a try. Thanks for the answer! – Kevin Smith Jul 30 '16 at 5:21
  • I think you're going about it all wrong. First, I bet you aren't letting the paint dry enough before you start sanding it. Second, don't use a palm sander, you need to do this by hand and in small sections. If you use any type of sander, it needs to be a random orbital sander. A palm sander will only leave swirls all over the place and totally mess everything up. Thirdly, I wonder if you got the surface clean enough to paint without having defects. Before you put paint on the car, you needed to have used a product like PrepAll. This will prevent fisheyes and a bunch of other issues with paint. – Pᴀᴜʟsᴛᴇʀ2 Jul 30 '16 at 12:16
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2000 grit sandpaper will still leave a pretty dull finish. You need to buff using some compound and a rotary buffer to get a nice shine.

Here is a door after I sanded with 2000 grit: 2000 grit sanding

And after buffing: enter image description here

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So, you have not posted pictures, but @M. Cooper gave a good answer, another possibility is humidity could cause similar issues... That is why the professionals use a spray booth - with temperature and humidity control.

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