Or you could wash it by hand with tsp or a similar product available at home centers and paint stores and rinse it thoroughly.
How to paint aluminum siding trim.
If you need to paint aluminum siding choose a day when the weather is at least 50 f 10 c and dry since moisture from rain or dew will ruin a new paint job.
When it comes time to paint aluminum siding the secret to success is choosing the right paints for the job in this case you will need an oil based paint as well as an acrylic based paint.
However you may find this too time consuming so cleaning with a pressure washer will likely work well enough to get ready to paint.
The key to painting aluminum siding is to get it really clean and to use 100 percent acrylic latex paint.
All of the chalkiness must be washed and scrubbed off and any flaking paint removed.
Then follow up by two coats of acrylic topcoat paint.
Apply one coat of acrylic primer.
Paint aluminum siding with acrylic.
In a nutshell you need to start with a clean palette.
Expect to pay the premium for good paint.
Coat your roller in primer and roll quickly and evenly along the panel of siding then roll backward in the opposite direction.
The key to painting aluminum siding is preparation and priming.
Check the label to be sure it s recommended for metal siding.
After your siding dries.
The best way to get this siding clean is to power wash it.
Then roll along the panel of siding quickly but with even pressure to be followed by moving backward in the opposite direction.
Prime the siding using a paint roller first coat the roller with primer.
Use it on the siding and you may find that using this sands down to the bare metal which would be the ultimate prep job.