I have an old house built in the early 1930s. The conventional stud finders are useless on plaster. The more sophisticated ones are more expensive in the $50 range.
What features would a stud finder need to have to work well in my situation?
What features do I need in a stud finder for use on plaster walls
plasterstuds
Related Solutions
From your description of putting a screw into the walls, it certainly sounds as if you have lath-and-plaster. Another sign is the color of the dust: with drywall, it will be very white and uniform, whereas with lath-and-plaster, it's greyish and has darker flecks.
A lot of stud finders work by detecting the change in the dielectric constant of the wall as you move horizontally across the wall. Stud finders have a hard time with lath-and-plaster because the plaster is solid and can often be 1/2" thick, then underneath the plaster you there are only small gaps between the wood lath, so you never really get the sharp change in capacitance that they look for. On the other hand, drywall is spongy so there's less material between the stud finder and the stud that it's supposed to be sensing.
I had a deep-scan stud finder, and it wasn't that reliable, but I developed a technique that I had reasonable success with: do several scans at different heights and different starting points on the wall, noting where it said there was a stud. I also found that scanning slowly was better than faster. Eventually, I would get to an "average" location that was a pretty good guess.
I later learned (at least in my house) is that there's a stud on each interior wall right where it runs into an exterior wall. I could then mark 16", 32", etc. back from that stud and be OK.
If your house was built before the 1940's, it's probably a layer of wood lath, followed by a standard 2x4 stud wall with no insulation. Perhaps some knob-and-tube wiring just to make things interesting. The plaster will make more dust than you thought possible (wear a mask).
After the 1940's, it's probably gypsum board, but without the foaming agents and plasticizers that make today's drywall easier to use. Behind it, you probably have a 2x4 stud wall with no insulation and conduit or NM wiring.
[Here's a picture of a lath wall from the back, courtesy Wikipedia]
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Best Answer
This stud finder with magnet and level is what I keep on me at all times. It is the only stud finder that I have and works excellently. It is strong enough to pick up nails used for crosses most of the time too.
I have no affiliation with the product - I am just a customer that has bought 6-7. The magnet is super strong and the pointer + level help. The only downside is the plastic tip breaks on every one if I drop it, but it still does the trick. A bonus is that it finds screws, nails, tools, whatever... in hard to see/reach places. I don't know how many times I was up in an attic and dropped something and pulled out the stud finder.