For heavy-duty jobs, consider using a respirator rather than a simple dust mask. [3] X Trustworthy Source Centers for Disease Control and Prevention Main public health institute for the US, run by the Dept. of Health and Human Services Go to source
Masking the car off is a delicate art. Do not use newspaper, as paint spray can leak through it and leave unsightly specks. Instead, use real masking paper, which is less porous and won’t let paint through. Also, be sure to tape every single edge of your masking paper down. Don’t just use a few small pieces of tape to get it to stay in place — paint can (and will) work its way under any loose edges.
If you’re experienced with auto painting, you might alternatively try stopping your masking a few panels back from your rust spot. If you know how to gradually blend paint, which is done when spraying, you can use this tactic to make it so that there isn’t a drastic color difference between one panel and the next.
After you’re done, feel with your (gloved) fingers — you should now have a smooth surface.
For this job, phosphoric acid is usually best and can be bought at most auto parts stores. If you want, use a hole spot filler or a body filler like Bondo to even out some of the dents and fill the space where the paint is gone. Finish application of your filler by sanding by hand (using 120 grit sandpaper) to get a nice smooth metal surface. See below for more extensive information on using fillers.
Wipe the area with mineral spirits or paint thinner. Tape newspaper on all surrounding areas within three feet.
For most primers, you’ll need to allow the fresh coat to dry overnight (at least 12 hours).
Let the paint set at least 24 hours before pulling off the tape. Be patient — if the paint still feels tacky, you may need more time.
As a precaution, never wax fresh paint within 30 days of painting — the scrubbing, buffing action can pull fresh paint off.
Getting rid of all of the rust is crucial — if you miss even a small fleck of rust, it can corrode underneath your car’s paint over time and lead to another rust spot. Keep in mind, that, because you’re using a grinder, all of the safety precautions at the beginning of the page apply for this method as well. That means wearing gloves, safety glasses and especially a dust mask to keep the rust and paint particles out of your lungs.
Believe it or not, cut-up beer or soda cans work well for hole-patching purposes. The aluminum in these cans is naturally corrosion-resistant and many modern cans are coated with a thin protective layer anyway. Another good choice is thin sheets of hard plastic.
Start grinding with a rough (low grit) sandpaper to smooth out big bumps, then gradually transition to a medium and finally a fine (high grit) sandpaper for a perfectly smooth finish. Slow, steady, hand-sanding is best for this process — mechanical grinders can tear your patch away.
Try to have the edges of your masking aligned with existing seams in the body of the car to hide minor differences between your new paint and the old paint (unless you’re experienced enough to produce a smooth blend).
You may want to buff out the edges of your paint and/or cover with a clear coat layer so that this section matches the finish on the rest of your car. Obviously, it’s important to pick a paint that matches your car’s current finish. There is a specific paint color code for each vehicle that can be found on a sticker somewhere in the vehicle. [11] X Research source This information is needed in order to match the color up. Most auto paint shops will be more than happy to help you with this. Keep in mind, however, that the paint on older cars can gradually discolor over time.
