The first stud finder I tried on our living room wall told me the entire wall was a stud. I slid it left and it lit up. I slid it right and it stayed lit. I recalibrated on a different spot, and it decided there were studs every four inches. That was Gary's old single-sensor model, which he handed over with one warning: "It's good on drywall." Our living room is not drywall.
The job was a TV and two shelves. The TV had been sitting on a dresser since we moved in, and Tessa wanted it on the wall, with two shelves beside it for plants and a wedding photo. Simple on drywall. On 1952 plaster, a little more interesting.
Why plaster confuses electronic finders
Downstairs, our walls are the original plaster: a hard, uneven layer close to an inch thick, over lath, over studs. An electronic stud finder looks for a change in density behind the surface. Drywall is thin and consistent, so a stud stands out. Plaster is thick and lumpy, and the lath behind it adds its own pattern, so the finder sees changes everywhere or nowhere. Outside corners and the areas around windows can be even worse if there's metal reinforcement buried in the plaster.
The two finders I bought
The Franklin ProSensor, $49. Instead of a single sensor it has a row of them and lights up the full width of what it thinks is a stud. On our plaster it was better than Gary's old one, but not reliable. On the wall left of the TV spot it showed clean, stud-width readings exactly where I expected them. On the TV wall itself it found one stud correctly and a wide, fuzzy band that turned out to be nothing. When it was good, it was very good. I just couldn't tell in advance which wall I'd get.
A magnetic stud finder, $10. This is a strong magnet in a plastic case. It doesn't look for wood at all. It finds the nails that hold the lath to the studs. Slide it slowly across the wall and it snaps to a nail head. Find two or three more nails in a vertical line above and below that one, and the line is a stud. It's slow, maybe ten minutes to map one wall, but on our walls it was never wrong.
The method I settled on: the magnet to find the nail line, the Franklin to show the stud's width so I could center the screws, and then one small test hole with a 1/8-inch bit in a spot the TV mount would cover. If the bit hits wood after the plaster and lath, you feel it bite. If it suddenly goes easy, you've found air.
Mounting the TV and the shelves
My first test hole found air. I'd skipped the magnet on that spot because the Franklin looked so confident, and I was about three-quarters of an inch left of the stud. The hole is behind the mount now, and nobody knows about it except me and whoever reads this.
A few things kept the plaster from cracking when I drilled for real: painter's tape over the spot, a sharp bit, the drill in regular mode and not hammer mode, and slow speed through the plaster before speeding up in the wood. The tilting mount went on with four 1/4-inch lag screws into two studs. I hung from it with one hand before the TV went up, which Tessa said was less of a test and more of a show.
One shelf landed between studs no matter how we shifted it, so that side got snap toggle anchors, which open up behind the plaster and hold far more than the little plastic anchors ever could. Before drilling anywhere, I also ran the Klein non-contact tester over the area and stayed clear of the line straight above and below the outlet, where wires usually run.
The cords run down the wall in a paintable cord cover. Fishing them inside a plaster wall is a project for another year, and possibly another person.
What I'd tell myself in January
Gary's rule for tools is "Buy once, cry once." This was the rare case where the cheap tool turned out to be the one that mattered. The $10 magnet did the real work. The $49 Franklin is a good second opinion and excellent upstairs on the drywall, but if I could own only one for the downstairs of this house, it would be the magnet. Together they came to $59, which is less than the TV mount, and the mount is the part I'll never think about again.
