Pour some sugar in a small bowl and add enough water to make a thin paste.
Dribble the sugar solution onto the concrete spatters, or use a rubber spatula to smear it on.
Wait five minutes for the sugar to soften the concrete.
Scrub the spatters with the scrubbing side of the sponge until they come free of the aluminum.
Sakrete makes a spray.
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Keep wetting the concrete until the top gets mushy and sand down with heavy grit sand paper. Then scrape with a sharp utility knife.