StudSensor™ stud finders locate studs by identifying increases and changes in density behind the wall. To function properly, the wall surface must have a consistent density level, and be less dense than the wood stud. Stud finders, however, will not always return accurate results with lath and plaster walls because of the very inconsistent method by which they are constructed.
Although walls may have a smooth surface, some walls deceptively hide an inconsistent combination of wood (lath) and plaster, with deep and shallow levels of density among the plaster, lath and stud. To fully understand why these walls present such challenges, it’s best to first take a look at how they’re built.
First, wood laths, narrow strips of wood, are nailed horizontally across vertical wall studs. Two wet coats of plaster are applied to the laths. A rough, sandy “brown coat” is applied, followed by a smooth, finish coat on top. After the plaster completely dries, the walls can be painted.
The photo to the right illustrates how plaster oozes through the lath to create curls called “keys.” Keys keep the plaster securely attached to the lath. Through insufficient “keying,” the plaster falls off over time. This keying creates the inconsistencies that challenge stud finding technology.
A MultiScanner® wall scanner with metal-finding capabilities or one of our dedicated metal scanners may be used to locate nails fastening wood lath to the studs. Mesh is also used to help secure the plaster to the lath in some instances. (In Scotland, they even used horsehair!) If metal mesh was used, even metal scanners may not find the stud.