The most important consideration in painting aluminium doors is the preparation. Paint does not adhere easily to bare aluminium. Aluminium surfaces are easily contaminated with fingerprints, oils, and other types of dirt. The aluminium must be properly cleaned and prepared before it can be painted. Proper preparation will ensure that paint will have a smooth and even surface and that it will not peel.
Remove the hardware from the door. Take off door knobs and locks. Protect the hinges with blue painter's tape. Protect the floor around the door with newspaper or a small painter's tarp.
Wash the door. The surface contamination needs to be removed. There are a number of factors to take into consideration. Paint does not adhere easily to bare aluminium, and, therefore, bare aluminium has to be cleaned and sanded before paint will adhere. If the door already has been painted, it still needs to be thoroughly cleaned. Wash the door with a mixture of high quality soap and warm water. Use a heavy-duty sponge and scrub brush. Allow the door to thoroughly dry.
Prime the door with oil-based primer. If the door has not been painted, it needs to be primed. Acrylic paint won't adhere to bare aluminium. If the door has been painted, it only needs to be primed if you are changing the colour of the door or if the old paint is in bad shape. The primer can be applied with spray or with a roller and brush.
Sand the door. Once the door has been primed, use a 120 to 150 grit sandpaper to sand the door. This will smooth out any bumps or uneven areas from the primer. Carefully clean off all sanding residue.
Paint the door with a high quality acrylic paint. Choose an appropriate size roller for the door. If the door is panelled, use a 4-inch roller. If the door is a flat surface, use a regular-size roller. Use a short nap roller sleeve on either roller. Begin by cutting in the edges and other areas the roller won't reach. Apply one coat. Inspect for drips and runs. Allow the first coat to thoroughly dry and then apply a second finish coat.
Make sure to use proper ventilation when working with oil-based primer. The fumes are very toxic.