We often get asked, why does my stud finder have trouble with lath and plaster when it works perfectly through drywall? Or, what is the best tool or technique for finding studs in lath and plaster walls?
Your Zircon stud finder finds studs by looking for an increase in density compared to where it was first calibrated on the wall. Drywall and other manufactured sheet materials have very consistent density, but lath and plaster walls have very inconsistent density on the backside of the wall. This is where the plaster is squeezed between the lath and ‘keys’ onto the back of the lath and holds the plaster in place.
So, even if the front of the wall has a very smooth texture, the back of the wall is what gives your stud finder trouble because there are changes in density everywhere as you scan.
As a result, your stud finder can show a false positive (a stud indication when it is actually not a stud) when it finds an increase in density, even if it is just a glob of plaster.
The best solution is to use a Zircon MultiScanner® wall scanner that has Metal Scan Mode or one of Zircon’s dedicated metal detectors, such as the MetalliScanner® m40 or MetalliScanner® MT 6, so you can find the little nails or tacks that are fastening every piece of wood lath to the studs.