It may be helpful to wet the concrete which helps to soften and loosen it from the siding.
Remove concrete from metal siding.
Chip away small chunks of concrete from your siding with a putty knife.
Hold the tip about 2 feet from the siding and gradually reduce this distance until the concrete loosens and blows away.
In addition to aluminum this process can be used for galvanized metals block brick and metal building panels.
While preventing buildup while you work is the best defense you cannot always do so.
Applying a concrete dissolver is one tactic used to soften old mortar on masonry tools equipment and vehicles.
Any splatter can then be removed with a water hose making the cleanup extremely easy.
For areas with a large amount of splatter using a putty knife may not be feasible.
For siding that has a porous or faux wood grain spray the affected area liberally with white vinegar to soften the concrete while scrubbing it away with a stiff bristled brush.
Step 3 keep the wand horizontal or angled downward.
Then scrape off the concrete gently with a putty knife.
The tip should never point up this orientation allows water to get under the siding and soak the sheathing creating possible mold and rot problems.
A number of sugar based commercial products are available to remove concrete.
The paste keeps the splatter from sticking and does not allow the concrete to etch the metal.