Do Stud Finders Work Through Exterior Stucco Walls?

Stucco

• Stucco is a mixture of cement and sand, and sometimes lime, mixed to a paste with water and applied to a wall. The dehydration of the water from the mix creates a hard, weather-resistant skin. Stucco and plaster are applied in similar fashions to serve similar purposes, but where stucco is traditionally used on a building’s exterior, plaster is invariably used indoors. Stucco can be applied by hand, using a trowel, or with a special stucco sprayer. Regardless of application method, a mesh is almost invariably attached to the outside of the building before the stucco is applied so that it has something semi-rigid but with good porosity to cling to as it dries.
  Metal chicken wire is by far the most common material used as the mesh. Although specialist mesh is available designed specially for stucco support, it is also typically made from metal. Technological advances have brought specialist reinforced fiberglass mesh onto the market, and traditional stud finders work well through that.

Stud Finder Technology

• Magnetic stud finders are the most cost-effective on the market. As the name suggests, they use an internal magnet that responds to the proximity of metal, which then turns the readout dial. Their real function is not to locate studs but electrical wires, and gas and water pipes that run up the inside of the wall. They work well for identifying studs, however, because the rows of fasteners -- typically nails -- that hold the stucco’s substrate to the studs will be located, thereby identifying the location of the stud itself. This system has distinct limits in that the user has to stumble upon the location of a screw or nail-head with almost pinpoint accuracy before the magnet reacts. Magnets are confused by the presence of a metallic mesh.
  Electronic stud finders typically have digital readouts and are designed to sense differences in the thickness of the wall they are passing over. Once calibrated to the thickness of the substrate, usually drywall, they react to the extra thickness of a stud. Because they rely on the transmission of an electronic field to work, they are also confused by mesh inside the wall.

Specialist Stud Finders

• Specialist stud finders, which cost more, work through metal. Available from some department stores and most home improvement warehouses, these tools typically have a setting dial or knob that allows for the signal strength and response sensitivity to be adjusted. The settings normally go from “Low” to “High” and then to “Metal.” These units will find studs inside a stuccoed wall.

Alternative Methods

• Studs can be located without the use of a specialist stud finder. The easiest and most accurate way is to gain access to the in-wall void through an electrical outlet: If an electrical outlet is anywhere on the exterior wall, first disconnect the power supply at the fuse box, then remove the faceplate and wall box. Poke a length of stiff wire, such as a metal coat hanger, horizontally through the hole left by the wall box; make a mark on the wire when it stops moving because it has hit a stud. Repeat the exercise to the other side of the hole. You now know where the two nearest studs are, and the distance between them -- the distance is usually 16 inches center-to-center -- so you can calculate where all the other studs are across that wall.
  If no electrical outlet is available use a stud finder on the interior wall, measure where the studs are, then transfer those measurements to the outside.