A viewer caught our TV cameras in a renovation centre and asked about cleaning aluminum siding.
An interesting fact about siding is that white aluminum siding and to some extent white vinyl siding both tend to "chalk". If you run your hand over it, you get a bit of a chalk like deposit on your hand. This does not need to be cleaned off. In fact this chalking action is purposefully built into the finish as it is this "self-cleaning" aspect of white siding that keeps it from turning yellow in the sunshine.
Two tips for cleaning:
For Aluminum and Vinyl, always clean from the bottom of the wall up. If you go from the top down you will create dirty streaks through the dirt below that are hard to remove. Allowing the grime to flow over the clean surface doesn't create these streaks. (Note: Brick walls are first soaked from the bottom up, then cleaned from the top down never letting the lower brick dry.)
Never point a hose or power sprayer up-hill in such a way as to push water under the siding through the weep holes. The soap can actually cause damage to your building paper that is behind the siding, leading to future problems with the wall. Always spray horizontally or even slightly downward. For more information check out: Improper power washing can damage the inside of your walls.
My favorite trick to be able to gently scrub the siding without a lot of water pressure, is to use those spinning car wash gadgets that attach directly to your hose. The water doesn't tend to shoot up under the sideing, you can add any soap you want and the gentle scrubbing is unlikely to remove any paint.