Finding studs in an old house

Why electronic detectors fail here

A capacitive stud finder works by sensing a change in density behind the wall surface. On modern plasterboard that works well: 10mm of uniform board, then either a void or a stud. The contrast is obvious.

Lath and plaster is a different material entirely. Thin timber laths are nailed horizontally across the framing at roughly 25 to 40mm spacing, then lime plaster is pushed through the gaps so it squeezes out behind and locks on. What the detector sees is dense, uneven material with timber running through it everywhere. It will beep in a dozen places across a metre of wall, and most of those are laths.

This is the single most common cause of a failed DIY mount in an older home: the detector said stud, the screw went into a lath, the lath let go, and the plaster came with it.

Method one: magnetic detection

The most reliable method on old walls, and the cheapest. A magnetic stud finder does not look for timber, it looks for the metal fixing the timber. Every lath is nailed to every stud it crosses, so the nails form a vertical line running straight down the stud centre.

1. Move the magnet slowly over the wall in a horizontal sweep at about chest height until it grabs.
2. Mark that point.
3. Move up 150mm and sweep again. Then down 150mm. You should find hits in a vertical line.
4. Three or more hits in a straight vertical line is a stud. A single isolated hit is a random nail, a picture hook or a pipe clip.

The vertical-line test is what makes this method trustworthy. Do not skip it and act on one hit.

Method two: tap and listen

Useful for narrowing the search before you reach for a magnet, and free. Tap firmly with a knuckle across the wall. Over a void you get a slightly hollower, longer note; over a stud it is shorter and duller. On lath and plaster the difference is far subtler than on plasterboard, so treat this as a hint rather than an answer.

Two things make tapping more useful. First, work along a full metre and listen for the pattern rather than an absolute sound. Second, tap at the skirting where the wall is often thinner and the change is easier to hear.

Method three: the confirming probe

This is the step that turns a good guess into certainty, and it is the one most people skip.

1. Pick a spot the mounting bracket will definitely cover. If you are unsure of the final bracket position, probe low and mark it, then patch later.
2. Use a 2mm bit and drill slowly.
3. Read the feedback. Plaster is gritty and gives way easily. Then you may hit a lath: about 8mm of soft timber, then void. A stud is different. It resists continuously and the bit keeps producing clean timber shavings well past 20mm.
4. If you hit void after a lath, move 20mm sideways and try again. Work outwards until the resistance becomes continuous.

Never probe blindly near a power point, light switch or directly above or below one. Cables run vertically to those fittings. If you must mount in that zone, use a detector with live-wire detection and treat its warning as absolute.

What spacing to expect

Modern Australian framing is 450mm or 600mm centres and is generally consistent. Older housing is not. In pre-1950 homes 400 to 500mm is typical, but genuine variation across a single wall is common, particularly where a doorway was moved or a chimney breast was filled in.

The practical rule: find one stud, measure to the next, and confirm the next one independently. Do not find one stud and mark out the rest with a tape measure.

Signs you have found a lath, not a stud

• The detector reports studs every 30 to 40mm across the wall
• The probe hits timber at 8mm depth then breaks into void
• A screw bites, then suddenly spins free under light load
• A hairline crack appears in the plaster as you tighten

That last one means stop. The plaster keys behind the wall are breaking away.

In a Hobart house specifically

Hobart has some of the oldest housing stock in Australia, so this is the normal case here rather than the exception. Two local wrinkles are worth knowing.

The framing is usually old-growth hardwood, far denser than modern pine. That is good news for holding a television and bad news for your drill: pre-drilling is mandatory, and a screw driven without a pilot hole will snap or split along the grain.

Second, in the inner suburbs where houses have been renovated repeatedly since the 1890s, you will occasionally find framing that has been cut out and never properly reinstated. If you probe a run of wall and find nothing solid over 600mm, that is what has happened, and it is a good moment to stop.

More on Hobart wall construction and what each type will hold, or have us mount it.

Reviewed: August 2026