Flat gray paint jobs require slightly more than just purchasing a spray can of primer from your local hardware store and shooting your shiny car with it. In order for the paint to stick properly, you must first prepare and clean the surface of the car, then ensure that you are applying paint, not primer, to the surface, due to primer's tendency to become powdery when exposed to the elements.
Wash the vehicle thoroughly with soap and water, being careful not to miss any leftover spots of wax or grease that might have been left behind in the past. Remove any chrome or plastic trim using the ratchet or screwdrivers.
Mask off trim that cannot be removed using the masking tape and paper. This includes the window glass, inside trunk and the engine compartment. Ensure that the masking is airtight, as paint can be blown through small crevices to damage or discolor parts.
Use a rag soaked with wax and grease remover and a dry rag to wipe the surface of the vehicle. Use the dry rag to quickly remove the wax and grease remover applied to the car so that it does not evaporate by itself. This will allow the wax and grease trapped in the removing chemical to redeposit on the vehicle surface. Wipe the whole car completely, then use two fresh rags and repeat the process.
Use the gray or red scratch pads purchased from an automotive supply store to scratch the surface of the vehicle. The ideal paint surface will have no shine to it. The red scratch pad is much coarser than the gray, so you will not have to press hard for the paint to be properly scuffed. Scuff the car everywhere you intend to paint.
Wipe the car one final time with wax and grease remover to remove any traces of oil from your hands as well as the leftover scuffing dust. Wipe the car dry, then wait five minutes.
Spray the surface of the car with the flat gray spray paint, being careful to avoid missing any spots, particularly on the bottom of the rocker panels or the underside of the hood or trunk lid. Apply the paint in heavy, even strokes, overlapping each pass of paint with each new pass. First paint the hood, then the roof and trunk. Paint the driver's fender next, then work around the car in a counterclockwise manner to ensure that the paint covers every panel completely. Allow the paint to dry completely according to the package instructions before attempting to touch the vehicle.
