Make sure you have the right kind of paint for whatever the door is made out of. So exterior gloss for wood and ferrous metals. You may get away with exterior gloss for aluminum, BUT because of the high thermal conductivity of aluminum, the paint will stick better (and last longer) if it's especially formulated for aluminum: So try to buy instead the sort of paint marketed as 'Garage Door Paint'.
Of course there are other things to think about. Bare metal or wood surfaces need to be primed with a suitable primer paint. There are specific primers for non ferrous metals (like aluminum). If only quite small areas need to be primed, you may be satisfied using an generic exterior metals primer on aluminum -- but keep in mind that this primer will be weaker than the 'proper' stuff and the paint job may need redoing sooner than you would otherwise like.
In most cases, your door will still retain much of its original paint and primer. As with any painting job, make sure all surfaces are clean and free of any rust or flaking paint. First clean the door thoroughly. To remove loose paint use a normal paint scraper. Next, scrub the door with wire wool (you should wear safety glasses for this) or use a pressure wash to remove small flakes. After that, you may want to lightly sand the door down in the flakiest areas, or just rub them hard with a rough cloth.
There are special cases, too, of garage doors that have to be recoated differently. For instance, if the door is made of anodised steel, or powder coated steel, ordinary paints won't adhere to it well at all. In those cases you should have a large label on the door saying that it has been powder undercoated at the factory where it was manufactured. You'll need an extra strong adhesive paint to use as primer in such cases.
Exterior paints almost universally are high in volatile organic compounds (VOCs). So the job will be smelly, and the paint brushes will need to be cleaned in white spirit or other strong chemicals afterwards. Wear old clothes and try to paint in slightly windy conditions. It goes without saying that the conditions must be dry, too, ideally for the first 48 hours after the paint is applied. Aim to have two overcoats as well as the primer.
NB: I have assumed throughout that you meant an exterior door that is opened to let the car in and out, not a door just for people!
Of course there are other things to think about. Bare metal or wood surfaces need to be primed with a suitable primer paint. There are specific primers for non ferrous metals (like aluminum). If only quite small areas need to be primed, you may be satisfied using an generic exterior metals primer on aluminum -- but keep in mind that this primer will be weaker than the 'proper' stuff and the paint job may need redoing sooner than you would otherwise like.
In most cases, your door will still retain much of its original paint and primer. As with any painting job, make sure all surfaces are clean and free of any rust or flaking paint. First clean the door thoroughly. To remove loose paint use a normal paint scraper. Next, scrub the door with wire wool (you should wear safety glasses for this) or use a pressure wash to remove small flakes. After that, you may want to lightly sand the door down in the flakiest areas, or just rub them hard with a rough cloth.
There are special cases, too, of garage doors that have to be recoated differently. For instance, if the door is made of anodised steel, or powder coated steel, ordinary paints won't adhere to it well at all. In those cases you should have a large label on the door saying that it has been powder undercoated at the factory where it was manufactured. You'll need an extra strong adhesive paint to use as primer in such cases.
Exterior paints almost universally are high in volatile organic compounds (VOCs). So the job will be smelly, and the paint brushes will need to be cleaned in white spirit or other strong chemicals afterwards. Wear old clothes and try to paint in slightly windy conditions. It goes without saying that the conditions must be dry, too, ideally for the first 48 hours after the paint is applied. Aim to have two overcoats as well as the primer.
NB: I have assumed throughout that you meant an exterior door that is opened to let the car in and out, not a door just for people!
