This way you can know exactly where the stud starts and ends in a horizontal direction. You can tell when the bit gets through the wall into empty space, versus when it just keeps on drilling into a stud. Then I drill a series of holes, using a long small-diameter bit, horizontally.
![stud finder for plaster and lath walls stud finder for plaster and lath walls](https://ninjadiy.com/wp-content/uploads/2019/09/plasterboard-walls-1024x767.jpg)
Using the wall knocking process I narrow down the search zone. My other technique (our house is old with plaster/ lath walls) leaves more marks. It does not depend on finding iron nails. This is very much like the knocking technique, but more sensitive that the manual way. Some of the better stud finders work differently, using a method I don't really understand to detect differences in density of the wall. This is not very precise, but it gives you a good area to cover more carefully with the stud finder. Usually you can detect a change where the stud is holding the front covering tight. Move your spot sideways and listen to the sound. As a fist step to find the stud, try knocking on the wall with your knuckles or a gentle hammer tap. And secondly, those nail heads are topped by a much thicker layer of plaster than the small covering of spackling compound used to hide sheetrock screws. First, the nails used to fasten the wood lath strips to the studs are much smaller than the screws used for sheetrock, so they are harder to find with a magnet. Now, if (as suggested above) the wall covering is plaster over wood lath strips, that makes it more difficult for two reasons.
![stud finder for plaster and lath walls stud finder for plaster and lath walls](https://www.yamanelectronics.com/wp-content/uploads/2023/03/image-31.jpeg)
So you have to scan the stud finder slowly back and forth, up and down, to find a metal screw. Typically these screws are positioned about 12" to 16" or more apart vertically along a stud, and the studs are spaced 16" apart horizontally.
![stud finder for plaster and lath walls stud finder for plaster and lath walls](https://ixooshop.com/wp-content/uploads/hardwares/1073470_3.jpg)
A lot of the simpler stud finders depend on detecting iron nails or screws used to fasten the sheetrock to studs.