Stud Finding Question #4

Our StudSensor™ stud finders identify studs by looking for increases in density behind a wall. (See How do stud finders work in the FAQ section for additional explanation.) In order to work properly and effectively, the wall surface must have one consistent level of density, and be less dense than the wood stud. Unfortunately, our StudSensor™ stud finders will not always return accurate results with lath and plaster walls due to the very method by which they are constructed.

The smooth surface of these walls deceptively hides an inconsistent combination of wood (lath) and plaster, with varying levels of density between 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.

For centuries, lath and plaster had been the primary building process for interior walls. In much of the U.S. its use began to decline in the late 1950s as drywall emerged as a less expensive and easier to install alternative. South Florida construction didn't follow the national trend as lath and plaster remained the dominant technique there through the early seventies.

The process begins with wood laths--narrow strips of wood nailed horizontally across vertical wall studs. Two wet coats of plaster get applied to the laths. A rough, sandy "brown coat" goes first and a smooth, finish coat follows on top. After the plaster completely dries, the walls can be painted.

The photo on the right illustrates how plaster oozes through the lath to create curls called "keys." Keys keep the plaster securely attached to the lath. Insufficient "keying" and the plaster falls off over time. This keying creates the inconsistencies that defeat the StudSensor™ technology.

All may not be lost! You can use a MultiScanner® tool with metal-finding capabilities or one of our dedicated metal scanners to locate nails fastening wood lath to the studs. In some cases, mesh is used to help secure the plaster to the lath. (In Scotland they even used horsehair!) Unfortunately, if metal mesh was used, even our metal scanners may not help you find the stud. As first-hand experience has told you, this is merely one of the many complications found in older construction projects.