Aluminium's great durability, weather resistant properties and heat insulation properties make it a fine choice of material for house siding, particularly in the more brutally hot parts of Australia where toughness and insulation really matter. However, aluminium siding does tend to dull and oxidise over time, and many people with aluminium siding choose to paint their siding when it becomes a little old and battered, or when previous coats of paint inevitably start to peel. The bad news is that aluminium is not the easiest material to paint successfully. The good news is, with a little care and prior preparation, well painted aluminium siding can stay looking good for years or even decades.
Aluminium takes paint best when it is as perfectly smooth and clean as you can make it, so any painting job must be preceded by a thorough cleaning job. The natural oxidisation process of aluminium produces a layer of chalky oxidisation on the surface of your aluminium, and this is often accompanied by clusters of lichen and mildew. Use a robust metal cleaning solution to remove these defects. Make sure to scrub to remove caked-on deposits (pressure washers are useful here if you're not too fond of ladders).
If your siding has taken any dents or damage, these should be ironed out prior to painting. Any small holes and pits in your siding can be filled in with a standard metal filling compound. Any remnants of a previous paint job should be chipped off and removed. Once your siding is clean, let it dry thoroughly before undertaking the next step.
To further aid the adhesion of your paint to your aluminium, any paint job should be preceded with a coat of primer.
Latex primer is a common choice for many outdoor painting projects, but should never be used with aluminium siding. This is because the vast majority of latex primers and paints contain ammonia, a substance which reacts with aluminium to produce small amounts of gas. This constant production of small amounts of gas builds up under the elastic surface of a coat of latex primer, causing your paint to bubble and crack in short order.
As a result, you should only used oil-based primers for priming aluminium siding. These primers tend to take much longer to dry and can be more difficult to find, but they provide a smooth and totally inert base for your paint to adhere to.
Choosing a paint
Your paint choices are less limited than your primer choices, although for the aforementioned reasons latex paint is not recommended. As long as your paint is suitable for aluminium and is formulated for outdoor use it will usually perform well. To ensure good results, choose an acrylic exterior paint, as these paints are highly resistant to fading caused by sunlight and will not flake easily.
You will also have to choose between a matte or gloss finish. Gloss finishes provide limited reflection of the sun's heat and are highly durable, but tend to flake and chip in an unsightly manner once age sets in. Matte finishes are generally more durable, but eggshell and satin-effect paints will put up with even more punishment if you want your siding to stay looking new for as long as possible