First, I'm not the handiest of men, but can usually figure this sort of thing out. I just moved into an apartment in Manhattan and we're wanting to mount shelves, desks, and televisions to the wall to make use of our vertical space.
Classic of knocking on the wall led to no definable progress. I haven't torn a hole in the wall yet, but from what i'm seeing our building is using a technique of filling the gaps between studs with this brown/pink clay substance to prevent spread of fire, which in turn means the hollow knock doesn't exist. (thanks Google)
Roommate pulled out this little magnet thing which should pop when finding nails, well that worked at corners but only there- the corners are using metal fittings.
Electronic stud finder, I purchased one with a standard mode and a deep scan mode. Our sheetrock is about 1.25 inches thick making it a little difficult for this device to work- in addition to struggling with that clay i'm finding everywhere.
Next I drilled at every 16 and 24 inches given that's the standard widths between studs (also did a hole -/+ an inch for margin of error).
that tell tale sign where the drill bit pops through the wall i've not yet had due to this clay filling..
Anyways, I'm humbly accepting defeat and seeking any advice.. thanks!