Anyone who has every tried to paint over anodised aluminium without priming first knows that chipping and peeling is virtually inevitable. Because anodised aluminium is slick and non-porous, it just doesn't hold paint very well. However, if you need to paint over anodised aluminium, there are a couple of preparation techniques you can employ that will allow you to achieve an attractive, long-lasting finish.
Clean the surface of the anodised aluminium using water, washing-up liquid and a coarse brush. Rinse away all of the soap or you will have trouble with adhesion. Allow the surface to dry.
Pour etching primer into the paint pot. Fill it to no more than two-thirds capacity.
Apply the etching primer to the anodised aluminium using the paint brushes. Allow the primer to dry for two full hours.
Clean the brush at least three times using white spirit.
Apply oil-based paint to the anodised aluminium in the same manner as you did the primer. Allow the surface to dry for two hours. Apply additional coats as necessary.
You may use latex paint instead of oil-based paint. However, be sure to use a latex paintbrush to apply it.
Etching primer is ideal for conditioning anodised aluminium for paint adhesion. Do not use an ordinary bonding primer or the final finish may chip and peel.