All well and good but you need a permit once you get above about 5% solution. That isn't enough to do anything to a block the size I sent.
That must be a local law. I can go to the farm supply store in Le Mars and buy gallon jugs of "muriatic acid" (archaic name for HCl, and these jugs are a 33% solution, IIRC). I use it to lower the Ph of my folks' hot tub (quickly :whistling: ), but the jug says you can also use it to etch concrete. May come in handy here...