Cast aluminium garden furniture does not rust, but it can discolor and develop a pitted or rough surface. Aluminium is affected by air pollutants. The surface will appear to have fine grit stuck to the surface, but it will not wipe off. If you look at an aluminium letterbox that’s been exposed to the elements for a couple years you will see what happens to aluminium.
When exposed to air, un-coated (i.e. the stuff that hasn’t been painted) aluminium will develop a microscopic layer of oxide on its exterior. This layer acts as a barrier which protects the metal from the elements and prevents corrosion. This quality is the most appealing characteristic when it comes to choosing a material for making outdoor furniture. It will weather any climate and any amount of precipitation. Cast aluminium furniture is a dependable option for outdoor living.
Please note that care will depend on the condition of the aluminium.
Regular Cleaning of Cast Aluminium Garden Furniture
If surface is only mildly discolored, wash with soap and water, to which some mild household acid has been added; lemon juice, vinegar, or cream of tartar. Most water is slightly alkaline, so do not add ammonia, TSP or soda. Wash as needed during the season; wash at end of season. (Remember the darkening of aluminium pans when low acid or alkali foods are cooked… It blackens. When acid foods such as tomatoes are cooked in aluminium, it will become shiny.)
If surface is pitted, polish with a soap-filled steel wool pot cleaner, rinse and dry. All steel wool must be removed or it will rust and stain the aluminium. Wash and dry.
There are also a variety of commercial cleaners used for aluminium surfaces on boats and automobiles which may help clean extremely dirty aluminium. Do not use commercial cleaners on anodized aluminium. A coat of auto wax, or a silicon spray will protect aluminium from corrosion and pitting.
Coloured Anodized Aluminium
Use just a little washing up liquid and warm water to wash anodized aluminium. Rinse well. The anodized finish prevents any corrosion.