Small chips and blemishes are best repaired with a can of touch-in paint and a brush. For larger jobs, use an aerosol spray. If possible, work in a dry, warm, dustless but well ventilated atmosphere.
Metallic paint finishes contain minute flakes of bright metal, possibly covered by a coat of transparent lacquer. Aerosol and brush-on kits for these types of finish are available, but it is almost impossible to reproduce the exact shade because the mixture of paint and flakes is critical, as are the temperature and conditions in which spraying is carried out.
Except for small jobs, or spraying less obvious areas such as front-bumper aprons, it is better to have the work done professionally.
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Plain finishes are easier to match, but you must obtain the exact shade recommended by the car manufacturer - a slight colour variation is obvious.
Often the code number of the paint is stamped on the car identification plate, and a retouching kit can be bought from a main dealer for the make if not available from an accessory shop. If the code number is not on the plate, quote the car make, model and year, the colour name, and the chassis number (always on the plate).
How to spray aerosol paint
Some aerosols contain solvents which attack and crinkle existing paint. Always test an aerosol on a hidden area of paintwork as a check.
If the paint crinkles do not go ahead with painting the car, have the repair done by a professional paint-sprayer.
Before spraying shake the can hard for at least three minutes after the agitator balls inside begin to rattle.
Practise on a piece of metal before you begin spraying in earnest. Try a brief spray from a distance of about 12 in. (300 mm) and look at the results.
If there are specks in the paint which do not join up, the spray is too far away and will have a rough finish when dry. If the paint drips and runs, the spray is being held too close.
At the right distance the result should be a smooth, glossy coat without runs.
After spraying, always clear the jet by turning the can upside-down and pushing the button for two seconds or until the jet blows clear. Otherwise the valve and jet will become clogged.
Preparing the surface
After dealing with any rust or dents (See Patching rust holes), remove grease and wax from the surrounding paintwork, using a cloth moistened with white spirit.
Take the gloss off the paintwork with 600-grit wet-and-dry paper used wet. Rinse with plenty of clean water, and wipe dry with a chamois leather.
Masking the area
Remove all the badges and trim if you can. Badges may have push-on steel or plastic clips holding them on behind the panel. You can usually prise the clips loose with a screwdriver.
Some badges are simply pushed into plastic sockets and can be pulled off. A few are fixed by nuts behind the panel. Trim strips are generally sprung over a row of clips or studs. Some trim and badges are glued on.
Use masking tape to cover a grille, name plate or any other small item attached to a panel you are spraying.
Cover any you cannot remove with masking tape, exactly fitted along the edge. Wrap projecting items, such as mirrors, aerial, door handles and bumpers, with paper taped in place.
Try to make the boundaries of the new paint at panel edges, trim strips or other clear lines.
Lay a double sheet of paper on the roof, and stick a strip of 1 in. (25 mm) wide tape along one edge and overlapping it. Peel it off and stick the tape along part of the boundary tape. Repeat until the whole boundary is well masked. Remember that spray drifts through the smallest gap.
Priming, spraying the top coat and finishing the surface
Shake the can of aerosol primer hard and long. It is thicker than top coat, but easier to spray on.
Spray a thin coat on to the repaired area only - not right up to the boundary. Let it dry for a few minutes, then apply another thin coat, and go on until the repair is evenly coated and the primer blends into the sound paintwork.
Let the primer dry completely, then remove any blemishes by lightly rubbing with 600-grit wet-and-dry paper, used wet.
In the same way, remove primer from the existing paint near the masking tape, being careful not to rub through the paint. If you expose any bare metal, re-prime it and rub down again.
To spray the top coat, shake the aerosol and hold it perfectly upright. Push off the plastic cap protecting the spray button. Point it at a piece of masking paper in case it splutters when you push the button.
As soon as the spray has stabilised to a fine jet, spray a horizontal line across the top of the repair keeping the button fully depressed and moving slowly and steadily. Release the button.
Repeat slightly lower down, so that the second line just overlaps the first. Continue until the whole area is covered with a thin layer.
Do not try to make the first coat fully cover, or it will certainly run. And do not stop or start spraying on the area being painted. Wait a few minutes before applying the next coat to let it partly dry.
Apply a second coat, and go on in the same manner until you are satisfied.
As you spray on more coats, the paint will begin to blend with the existing paintwork. It may take six or more coats to give a good depth of colour.
If the paint runs, let it dry completely - wait at least an hour on a hot day.
Rub down with 400-grit wet-and-dry paper, used wet, until the surface is flat again. Dry off the water and continue painting.
Let the last coat become touch dry, then pull off the masking tape at an outward angle to avoid lifting off the edge of the new paint.
Leave the new paint to harden for a day or two, then blend in the edge by rubbing it gently with a damp cloth primed with a mild cutting compound - available from accessory shops.
If the new paint is dull, rub all over but not too hard or you may go through to the primer coat.
Leave the new paint to weather for six weeks before wax polishing it, which should bring it to full gloss.
Brush-painting a small area
Before carrying out a small paint repair, always remove any loose or cracked paint with a small knife blade. Hold the blade flat to prise off cracked paint.
Shake the can of paint thoroughly. Remove the screw-top and stir the paint with a piece of wire. Try not to use the rather basic brush fitted in the screw-top. Use an artists brush - it can be cleaned later with cellulose thinners.
Apply the paint quickly but not thickly, with the minimum of brush strokes. Overlap the sound paintwork by about 6mm.
Let the paint dry, then apply a second light coat.
Too heavy use of the brush risks stirring up the layers already painted and spoiling the surface finish.
Let the paint dry for at least 24 hours, then polish it gently with a mild cutting compound - not a heavy paste one - to blend the edges into the original paintwork.