you could drag a green crayola across the mortar to make a little fungus-look.
I watched a Tv movie prop painter age some brand new concrete with chaulk, mostly yellows and greys, when he got done it looked like it had been there for a very long time. It was the base to a statue that was also supposed to be very old.

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"My Insanity is well-respected, until they wiggle free and become a stringer for a tabloid"