Am I having trouble finding studs because my walls are lath and plaster?

Question

I picked a TV mount from Ikea. The TV itself is being mounted to some paneling which in turn is mounted to set of wooden draws. In addition, it gives you hardware to mount the panels to the walls. It's not really meant to support any weight, just to keep it from swaying back and forth. So I picked up a cheap stud sensor (Zircon E30) but I'm not having very good luck with it. As soon as I start sliding it, it usually just starts indicating an error. Occasionally it tells me there's a stud, but on subsequent passes the results are far from exact. Right now I think I have an idea of where two studs are but it's a very rough guess.

I'm wondering if this is because this model is junk, or could I have lath and plaster walls? I'm pretty sure the walls are not drywall, just judging from the way they have crumbled when I tried to put a screw in them previously. Usually the paper coating on plaster doesn't allow it to crumble like that. Plus drywall usually seems to crumble more into a fine powder and this crumbles more into sand or little pebbles.

So does anyone know if there's a way I can tell if the walls are lath and plaster? Or does anyone know if this stud finder is no good? They do make a slightly more expensive model which is supposed to work better with lath and plaster walls. I just don't want to go and spend the money buying if it I don't really need it. Plus I'll probably wind up using it this one time and never see it again.

Any suggestions? I did try knocking on the walls and trying to hear a difference, but that wasn't really working for me.

edit: I just wanted to let people know I used this sensor: http://zircon.com/products/metal_m40.html and it seemed to work pretty well. So if you have lath and plaster walls, might want to give that one a try.

Answer 1

From your description of putting a screw into the walls, it certainly sounds as if you have lath-and-plaster. Another sign is the color of the dust: with drywall, it will be very white and uniform, whereas with lath-and-plaster, it's greyish and has darker flecks.

A lot of stud finders work by detecting the change in the dielectric constant of the wall as you move horizontally across the wall. Stud finders have a hard time with lath-and-plaster because the plaster is solid and can often be 1/2" thick, then underneath the plaster you there are only small gaps between the wood lath, so you never really get the sharp change in capacitance that they look for. On the other hand, drywall is spongy so there's less material between the stud finder and the stud that it's supposed to be sensing.

I had a deep-scan stud finder, and it wasn't that reliable, but I developed a technique that I had reasonable success with: do several scans at different heights and different starting points on the wall, noting where it said there was a stud. I also found that scanning slowly was better than faster. Eventually, I would get to an "average" location that was a pretty good guess.

I later learned (at least in my house) is that there's a stud on each interior wall right where it runs into an exterior wall. I could then mark 16", 32", etc. back from that stud and be OK.

Answer 2

I took off the baseboard. With a hammer I broke off some plaster and found the studs. I found the height I wanted and drilled my holes, mounted the bracket then put the baseboard back on. It took about 45 minutes total.

Answer 3

Look for wall outlets. They are usually mounted on a stud. Then start measuring in 16 inch increments to find other studs. As a backup, I would use a small finish nail to hunt for the stud in the area that you want to put the TV in. Some studfinders have a "hi" and "low" setting that will adjust how sensitive it is to things behind it. Sometimes for instance, its harder on external walls because there is insulation in them. Maybe go to Home Depot or Lowes and buy another brand of stud finder. If it doesn't work you can always return it. Another kind of stud finder has a magnetic sensor and detects nails which are in the studs. You could try that type.

Answer 4

I've come to rely on a pair of neodymium magnets for all things wall-related. A single magnet will help you find studs (namely, the nails and screws in the drywall or lath), and help you avoid nailing into other nails and nail plates (or piercing your wiring).

AND, while not relevant to your current problem, having TWO magnets will even let you go one step further and let you precisely line things up across a wall. I just dragged some 300 feet of cable up two stories to my attic by only cutting two holes in my wall (at the top of each floor to drill through the wall plates) by using a pair of neodymium magnets to line everything up. No exploratory holes needed.

Answer 5

The first stud finder you mentioned does not have a dedicated Metal Scan mode and will not always return accurate results with lath and plaster walls because of the inconsistencies common in this type of construction method. For lath and plaster walls, without metal mesh reinforcements, you may be able to use a metal finder by detecting the nail heads that attach the wooden lath to the studs.

From the Zircon site

"Stud finders work 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.

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.

The keying in lath and plaster creates the inconsistencies that challenge stud finding technology."

Answer 6

You said the bracket is not carrying any weight, just to stop the TV swaying back and forth. Why not just use butterfly bolts then? They will hold just fine, especially if they are fixing a plate of some kind to the wall.