If you found some rust on the body of your car, and want to both make your car look fabulous again AND prevent the rust from spreading like the cancer it is....Here ya go
Step 0: First, you gotta clean the car. Good ol'fashioned car wash. Make sure it is dry afterward.
STEP 1 - GETTING RID OF THE RUST
Depending on the depth of your rust, you may be able to start with hand-sanding, or you may have to use a dremel.
1. Use 250 grit sandpaper to sand the paint and loose rust from the area so you can see the impacted area. Use a sanding block when sanding so you don't get wobbles in your surface. SAND IN AN 'X' PATTERN: First diagonally across the surface one way, then across diagonally the opposite way.
2. For deeper rust pockets, pick up a dremel and gently grind away rusty bits. I prefer using a metal-grinding disk so it has some give and doesn't go too deep too fast. Careful that you're only taking away the rust, and not good metal. If your rust hasn't gotten pitted yet, skip this step.
3. Use 200 grit sandpaper with a sanding block to evenly sand off any remaining rust. Clean and dry surface thoroughly.
4. Use Rust-Etching Gel (also called Naval Jelly) over the affected area. Use as instructed on bottle. This will etch away any remaining rust particles on the surface. Clean and dry.
Image: Rust Before
Image: Area after dremel, sanding, and etching.
STEP 2: PREVENTING NEW RUST
1. Epoxy Bare metal. Epoxy will seal the Oxygenout of the metal so it won't rust again. Apply a thin layer so the metal is coated. Let cure.
2. Apply bondo over uneven surfaces (where rust was pitted). Use a bondo-spreader to run across the surface and remove excess bondo. Allow to cure, and then sand with a sanding block (hard foam is best). Start with 200 grit dry sandpaper to knick off the rough bondo.
3. Once the bondo isn't super-rough, I'd start wet-sanding. You can use the water to see the reflections in the surface as if it were painted, so you can make sure you're making a smooth surface as you sand. I'd start with 300 sandpaper and slowly move to higher grit from there. Remember to sand in an 'X' pattern.
STEP 3: MAKING A BEAUTIFUL SURFACE
1. Tape off the car except where you want to spray Primer. I'd suggest bagging the entire car, since overspray is a mystical and evil force. You can use painters tape and trash bags. Give yourself a little extra room around the sanded area, or the thick primer will leave an edge where you taped. You want to be able to feather the primer.
2. Spray the primer. You CAN use a rattle-can primer, but I really don't recommend it, especially for larger areas. Pick up Catalyzed Primer (follow the mixing directions) from an automotive paint store (like Finish Masters), and a cheap gravity-feed paint gun (Harbor Freight sells them for $15). Hook it up to a Air Compressor and you are all set. Careful to stand back a few feet when you spray the primer. Test spray a piece of cardboard so you can get a feel for how it works if you've never painted before. Use long strokes across the body, passing past where you want to paint each time. Start with one light coat, let it sit a couple minutes, then paint your first 'real' coat. This prevents drips. If you DO get drips, don't stress, you can just sand them away. You'll probably need a couple rounds of primer, sanding between each. Your first round should be 2 coats, then just 1 after that. Make sure to clean your paint gun! Acetone works great. Also, wear gloves and a mask when painting. Be safe!
**if you decide to use rattle-can primer, make sure it is high-build. SEM makes a great one
3. Start sanding the primer. I'd start with wet-sanding sandpaper at about 300 grit, then slowly move to higher grit. Make sure you're sanding in an 'X' pattern, using a hard foam sanding block. Just soak the sandpaper in a bucket of water, and periodically use a soaked cloth to clean the surface as you sand. Look at the reflections on the wet surface - you should be able to see nice smooth reflections so you know you're not sanding lows into your body. Feather your sanding efforts out to the edges so it blends nicely with the remaining paint.
4. If you're sanding in an area that has edges or design lines, details...make sure to mask off the edges as you sand. Use 3M Vinyl tape so it sticks to the surface as you wet sand, but doesn't harm your paint or leave a residue. Tape one side, sand against it, then tape the other side, sand against that.
5. Clean the surface. All done! You can paint, send it to a shop to paint, or just let it be. Either way, you don't have to worry about rust anymore! If you decide to paint, I recommend against rattle-can paint. You can get the exact BMW color of paint from Finish Masters, and use the same gravity-feed gun to paint. I DO recommend a separate gun for your clearcoat.
Masked off car ready for primer, with all that awesome protective gear and cheapie Harbor Freight paint gun! Make sure to cover the whole car!!
Using 3M Vinyl tape to hold edges on the window. Notice the area that was once pitted, uneven, and rusted, is now smoooooooth!
Primered surface with tape to keep edges. Top has not been sanded (notice hard edge), bottom has been sanded (notice feathering)
And here's the 3M tape I recommend:
this is the first article I've attempted, please let me know what you guys think!