Even if you know how to use a stud finder and are doing it correctly, the devices may not be as effective for plaster walls. Because plaster walls are thicker, harder and more brittle than drywall, finding a stud can be a bigger challenge.
Listen for a deep thud when you knock on your wall.
If you hear an echoey hollow sound, it means there's nothing behind the wall where you're tapping. Move across your wall and keep tapping until you hear a solid thunk, which means there's a stud behind the plaster.
If you are looking for the best stud finder for plaster walls, do not overlook the Zircon M40. It is basically a sensitive metal detector. The Zircon Metalliscanner M-40 ... (find on Amazon : Zircon MetalliScanner m40 Handheld Electronic Metal Detector For Use on Dry Wall, Concrete, Lathe and Plaster, Stucco and More.
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.
Generally speaking, it's best to hang heavy pictures on a wall stud. As mentioned earlier, the wall stud is where the wooden lath attaches to the wooden frame behind the plaster. Therefore, it's the strongest part of the wall and the ideal place to hang pictures from.
Using a wall anchor can protect your wall, your shelves, and everything on those shelves. They allow you to hang items without the use of a stud in hollow materials like drywall, and give much more support when used in solid material.
The Pushpin Test
All you need to do is take a simple thumbtack and try to push it through your walls. If the pushpin penetrates the wall, you have drywall. If it doesn't, you have plaster.
Generally, a plasterboard wall will hold a TV securely and safely, but this is only as long as you use the right mounting. You should consider using an anchor or mounting plate for best results.
Anchors. Anchors are some of the easiest ways to hang anything in the walls without a stud. These work in different ways to keep screws from slipping out of their holes or otherwise damaging the drywall.
FRAMED CONSTRUCTION
The minimum thickness over framed walls is 3/4-inch. Most all fire-rated assemblies require 7/8-inch and some require a full 1-inch thick cement plaster. Always refer to the fire-rated assembly test before making an assumption. One-coat systems may be applied as thin as 3/8-inch.
Basic Zircon StudSensor™ stud finders with only Stud Scan and/or DeepScan® mode are not recommended for lath and plaster walls. However, MultiScanner® models with Metal Scan mode (or a dedicated metal finder) can be used to locate the pattern of nails or screw heads attaching the wood lath to the studs.
Use a measuring tape, the knock test, or visual clues to find the initial stud, and then measure outward at the standard spacing to locate additional studs. A visual inspection may also allow you to notice wall imperfections, as stucco finishes may reveal slight irregularities or seams where the stucco meets the wall.
Franklin Sensors ProSensor M90 Professional Stud Finder
In our lab tests, it worked equally well through plaster, drywall, and paneling. Depending on the surface materials, the depth detection of this tool is between 1 and 1.5 inches, and it's always on deep scan mode.
Lath and plaster is a building process used to finish mainly interior dividing walls and ceilings. It consists of narrow strips of wood (laths) which are nailed horizontally across the wall studs or ceiling joists and then coated in plaster.
Another practice of finding electrical wires behind walls is to use a metal detector. This can be an efficient method if you know there are very few wires and if there aren't many other metal objects, like nails, in the walls. You can find out which wires are connected to which circuit breaker without any tools at all.
If your walls are plaster, you might also consider using a strong magnet or metal detector to locate the nails that were used in the wall studs. Move a magnet slowly across the wall until you feel it sticking slightly as it is attracted to a metal nail inside the wall.
One square meter of (properly installed) single plasterboard can support a weight of 15 kg. One square meter of double plasterboard can support 25 kg, and triple wallboard can support 35 kg. The studs reset the weight that the wall can cope with.
The best-rated product in Plaster Hollow Wall Anchors is the HTB 2-1/4 in. Drywall Anchor Bolt with Slotted Round Head Screw (100-Pack).
Plaster walls require drill bits that are designed to penetrate the hard surface without causing damage.
Unfortunately, there wasn't a regulated or realistic way to ensure that all older buildings using plaster walls were asbestos-free. Asbestos was commonly added to plaster until the late 1980s, as it was seen as an inexpensive way to add to the plaster's insulation and fire-retardant properties.
Use a toggle bolt or anchor to hang the piece on areas with no studs, This Old House says. The weight of the piece, and the thickness of the wall, will dictate the toggle size. The typical metal toggle bolt can hold 25 to 50 pounds on plaster, according This Old House. A plastic one can hold 10 to 25 pounds.
It's actually not too hard to hang things on plaster walls, however, as long as you use screws and work slowly and carefully. Pre-drill the holes, and use fairly long screws to ensure a secure fit. If you're hanging heavy objects, use screws with anchors for added protection.