Hi folks,
I've drilled into my bedroom wall expecting to hit bricks behind the plaster, as I have elsewhere in the house.
However, on this wall there seems to be a huge cavity, maybe 40mm, behind the ~30mm of plaster before I reach the brick, like this (cross section view):

((I think it's plaster anyway, not sure how to tell. It's white and quite crumbly. Apartment complex built in the mid-90s).
How can I hang things off a wall that's built like this?
Will I be looking for studs behind the plaster, or do I need super long screws to reach the bricks? My stud finder hasn't told me much with any consistency...
Thanks a mill for any hints, I understand it's hard to diagnose like this! Photos of the holes I've drilled don't say much, so I'm prepared to do some exploratory drilling if needed. I just want to hang some shelves, haha.
Cheers, Danny.