I just moved into my new apartment in Manhattan and I'm trying to get my TV mounted on the wall. The building was built in 1915 and seems to have plaster, not drywall. I've used various methods to find the studs, which all seem to agree on where the studs should be, but my first two holes hit nothing but air.
To find the studs, I started with a studfinder. It detects 3-4 inch wide studs with 16-inch spacing center-to-center. I have repeated this over and over and I always get the same readings with perfect consistency. One of these lines up with an electrical outlet in the wall. All of this is pretty typical for studs, right?
There were two layers I drilled through: the plaster (soft and easy, drilled through steadily), then a very thin hard layer, kind of like a shell. After that it was just air. The second layer definitely wasn't a stud; it was way too thin. I drilled a second hole, on what should have been a different stud, and the same thing happened.
After drilling, I tried the magnet trick to see if the studs were elsewhere. The magnet would fully stick to the wall at various points, all of which aligned with the studfinder's detection zones. The magnet sticks to what must be large nails or screws along these vertical "studs" every 13-15 inches or so. I can't find any outside of those areas.
I tried the hammer method but it all sounds the same, except above the outlet. Poking a stiff metal wire through the holes I drilled, I hit a firm surface at 3.25 inches in. I can't really tell what kind of material it is. I also tried looking inside the wall through the outlet, but underneath the cover plate it's absolutely packed with plaster. I would have to chisel or saw the receptacles out from the wall.
So, I'm totally stumped! Three different methods (studfinder, magnet, spacing from outlet) all point to a stud in the same place, but they're all wrong. My fear is that the surface behind the plaster is a masonry wall, and there are no studs; that would end my dream of wall-mounting this TV.