When you replace the fender on your car, you will usually need to paint it to match the rest of your car. Although many fenders are sold pre-primed, you will still need to do a little priming to remove imperfections. This is a do-it-yourself project that should be done in a well ventilated, semi-enclosed area, such as a large garage with the garage door open.
Determine the color code of the paint you need for the fender. Look on the information sticker on the driver's side door. There will be a series of letters and numbers that begins with ABA or ABB. Write down the code, including the ABA or ABB, and write down the next two lines of codes as well. If you have a single tone car, one of these lines will be blank. A two-toned car will have a code on both lines. Take this code to an automotive store that mixes custom paints and have them make you 2 gallons of this paint.
Wash the car thoroughly, concentrating on the fender. This removes dirt and debris so the paint has a smooth, even surface to adhere to. Allow the car to dry completely.
Tape off the area around the fender using blue automotive tape. You can use newspaper or plastic sheets to protect the tire, rim and at least a 3-foot area around the fender from over-spray.
Prime the fender. Due to the amount of handling during shipping, you will usually have to lightly sand the fender with fine grain sand paper, such as 100 grit, to remove any imperfections. Once you do this, you will need to apply a coat of spray-on primer from your local automotive parts store. Make sure that you use automotive primer.
Apply a base coat of paint to the fender using an automotive paint spray gun attachment hooked up to an air compressor. You should fill up the spray gun reservoir 3/4 of the way to allow it to flow properly. Using a brush is another option, but a brush will usually leave brush marks. Use long, even sweeping motions to apply the base coat evenly. Allow this coat to dry for at least an hour before adding another coat. Put two to three coats of paint on the car. Darker colors need more coats than light colors. Allow the paint to dry completely between each coat.
Spray a clear coat onto the paint, if necessary. You will need to mix the clear coat with hardener according to manufacturer's instructions, as these instructions vary. This adds an extra layer of protection and will make the fender glossy. If the rest of your car has a clear coat, you will have to apply one. Remove the tape and protective materials, and make sure that nothing touches the clear coat.
Sand the fender using 1500 grit sand paper and water 2 or 3 days after you apply the clear coat. This is known as wet sanding. Make sure that you have water to rinse off the debris from sanding. Keep in mind that you need to use a very light touch as you want to sand only imperfections and not the actual paint.
Buff the fender using an orbital buffer with an automotive polishing pad and rubbing compound. You can do this using fresh pads to increase the luster.
Always wear a respirator when working with automotive paint.