Concrete corrodes aluminum quickly. If this is a one-shot deal - if you just want to stamp a certain patch of concrete and then be done with it - then sure, go ahead and make your stamp out of aluminum. But if you want something that's going to last, that's going to be good for multiple jobs over a period of years, then look into using another material. Some kind of plastic - ABS, acetal, polycarbonate - would probably work fine. I think that's what Wizard was trying to tell you.
Andrew Werby
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