Ah. No. Definitely old.
I'll take some pics. There's some inside my brick bin shed (no airbrick).
Then there's some on the external wall where there's a gap between the bin shed and the wall. And then some on another bit.
Wall is bone dry. Brick shed gets swamped when it rains.
It's just soluble salts being left on the surface after the wall has got wet then dried out from the front face. Scrubbing it off and rinsing the salts off mostly works.
Ah. No. Definitely old.
I'll take some pics. There's some inside my brick bin shed (no airbrick).
Then there's some on the external wall where there's a gap between the bin shed and the wall. And then some on another bit.
Wall is bone dry. Brick shed gets swamped when it rains.