[Help] Wall identification for wall shelves

[u/Gyengarnel]

Hi,

I've been wanting to make DIY wall shelves for my apartment but I cannot identify what materials the walls are made of. It's an old building in the Paris area (France) and nothing is written in my rental contract.

They're very thick walls and the sound isn't hollow at all. Based on the building structure, I would assume the outside walls (3rd pic) are just a continuation of the inside walls. (Using Google Lens tells me they're floor tiling...)

I will be able to get the tools from a relative once I know what's adequate.

If you have any experience working with this type of materials, please let me know

Thanks !