About the only section on the forum to ask:
Apparently there is “limestone” (what I was told) leaching up from concrete (or something) under brick pavers into a door’s metal threshold area; the metal threshold butts up against these outside brick pavers. Is there a decent (safe, cheap, etc) chemical to eat it away/ clean it nicely. Carbonic acid? Vinegar/ acetic acid/ HCl/ muriatic acid. Almost every type of acid dissolves limestone, what would you suggest?
http://glenwoodcaverns.com/pdfs/Dissolv ... h-Acid.pdf
And if I don't see an immediate reaction then ok to letit dwell a while I assume.
I understand it takes water pooling in the area to create this “leaching limestone” problem So solving that drainage issue is a priority.