Listen very carefully when you do a knock test since the horizontal wooden slats behind the plaster could make a similar noise.
If the wall sounds hollow when you tap on it, then try to find another nail in the baseboards.
You may get inaccurate readings if your plaster wall has a wire mesh support.
The magnet picks up where the horizontal wooden slats are nailed into the studs. If you have metal slats or supports behind your plaster, then a magnet won’t give you conclusive results and you’ll need to try another test.
Magnetic stud finders won’t work if you have metal supports instead of wood behind the plaster. Stud finders are rather inexpensive devices that are easy to use.
Studs run vertically up the wall, so any that you find will span from the floor to the ceiling.
You can easily patch the hole in your wall if you missed the stud. Avoid using a hammer and nail on plaster walls since you could easily crack or chip the finish.
