Looking at the walls, from the inside of the building, it is poured concrete. Fun fact: The building itself was built in 1927.
As for what's on the outside, under the stucco, I have no clue.
Bugs could be an option, hadn't thought of that. Now that you mention it, their are damaged spots on the bottom of the building, from "lawn maintenance". And a corner where the stucco has separated, due to a water leak from inside.