Acid washing brick buildings

[DoubleH]

Another "What the hell IS This?"

I’ve seen this before, but thank goodness not often. So I clean this brick home, and this is under the funk: [IMG_0617] It’s impervious to SH, AND 8-9 GPM @4KPSI. What is this white stuff and what will remove it?

Or search one restore in the magnifying glass, top right