From their website.....
Simple Green is extremely effective at cleaning siding (aluminum, vinyl, cladding, stucco, etc.) If your siding is not heavily soiled and you have access to a pressure washer or steam cleaner, a 1-part Simple Green to 30-parts water dilution would be best. If you will be manually cleaning the surface, use a 1-part Simple Green to 10-parts water dilution. Work in sections so that the Simple Green solution does not dry on the surface prior to rinsing. Best results come from starting on lower areas and working upward, to avoid making “clean streaks†that are very difficult to even out.
If you are trying to remove grease buildup on your siding from a vented exhaust, manually clean the area with a 1:5 dilution using a rag or sponge. Test this dilution first and increase strength as necessary, to a strongest solution of 1:1. Wash in small sections and rinse with water before solution dries.
If your siding has a powder coat, you may experience some color runoff due to removal of oxidized paint. This removal is essential for maintaining your siding and in no way damages the paint or powder coat. If your aluminum is bare, please remember that Simple Green will remove all grease & soil. This means that you will have raw, unprotected aluminum exposed to the elements. We recommend using aluminum paint or some other sort of protective coating after cleaning to prevent oxidation of the metal. If the aluminum already has any sort of oxidation or discoloration from weather staining, Simple Green will not remove this. Simple Green will only work on dirt, pollution, biological soils, grease or oil that is on the surface.