Something a lot of folks miss is what acid does to that black crust on a molecular level. That gunk is mostly carbon and soot from decades of coal smoke, and acid attacks the mineral deposits holding it to the brick, not the carbon itself. So the rinse is what really does the work, and if you let the mix dry on the wall you can end up staining the brick or burning the mortar joints. Heat matters too, that acid will eat faster on a 90 degree day than a cool morning, so mix and rinse smaller sections when it is hot out. Baking soda does neutralize it, but honestly a good long soak with the hose and a scrub keeps it simple if you are quick about it.

Man, 1,800 pounds is wild. That grinder has been through a whole life with you. I feel for you on those Portland bags, nothing worse than paying good money and getting a flat cup because the burrs are shot. Six years is a long run, so yeah, a fresh set will probably feel like a totally new grinder once you break them in.