Here are the basics on preparation for painting with a roller. It’s hard to give one set “recipe” for prep because each project is at least a little different. Here a couple suggestions:
General Suggestions
1. Treat each panel separately.
Some areas may require more work than others. There may be rock chips on the hood or behind the wheels, rust on the fenders, and clear coat problems on the roof, but the doors are just dull. Don’t make more work for yourself by over prepping panels that are in decent shape. If there is solid factory base to work with, chances are it’s got good adhesion to the metal, and a little scuffing with a Scotchbrite pad and a shot of wax remover and degreaser is all it needs.
2. A prepared surface doesn’t have deep scratches.
You can save yourself some work if you lay down some high-build primer over the top of your body work, then sand a little with 320 or 400 grit sand paper. If you’re not painting over body work, don’t worry about this.
Rust Removal
Rust can cause all kinds of problems down the road, possibly ruining the work you put into your paint job. Even though Rustoleum is a rust-inhibiting paint, removing obvious rust spots is cheap insurance. Use rough sand paper (something like 36, 60 or 80 grit) or a wire wheel to remove the rust. This is the time to use your electric or pneumatic sander to get rid of the “tin worm.” If you don’t have power tools, use a small-ish sanding block to concentrate your efforts on the rust without doing a ton of extra work.
Shaping
The amount of time you spend shaping depends on how straight the body panels are. If you have dents and dings that are deeper than body filler can hide (around 1/8th inch), you need to do some metal work. There are specialized tools to push and pull metal back to its original shape, but that goes beyond the scope of this site. We’re trying to get results without expensive tools or paying someone to use their expensive tools.
When the body panels are mostly straight, you can use body filler and putty to even things out. The general idea is to fill in the low spots, building a small area that is higher than the surrounding area. Then you sand the newly created high spots down to be level with the surrounding area.
Smoothing
The paint you will use is self-leveling, but that doesn’t mean it will hide 80 grit sanding scratches! I know this because I tried it. To test the limits of “self-leveling” for Rustoleum enamel, yeah that’s it…. just a test! The amount of smoothing you do at this stage depends on how much color you want to remove later. I learned that dry sanding with 320 grit before you start on color coats is a lot easier than wet sanding all the color off, only leaving paint in the scratches. Very artistic, but not what we’re after!
Scuffing
For areas that didn’t require any body work and have solid paint (no cracking, peeling, clear coat failure, etc.), you can just scuff the surface with a Scotchbrite pad. Don’t go crazy with the scuffing, just take the shine off. Agressive sanding of solid paint just makes for more work.
