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The wall has a picture rail, a hundred years of paint and not one crack. Then the new TV arrives, and somebody has to drill the first hole.
Plaster holds a TV well, as long as the TV is not hanging on the plaster. The bolts go through it into the wood studs behind. The job is to get through a hard, brittle skin without cracking it, find the studs it hides, and use bolts long enough for a wall thicker than drywall.
Can plaster walls hold a TV?
Yes, when the mount is bolted into the wood studs behind the plaster. The plaster is a brittle skin, usually 3/4 inch to just over 1 inch thick, and holds nothing heavy on its own. Find the studs, drill slowly through tape, and use lag bolts long enough to pass the plaster and bite into the stud.
How to mount a TV on a plaster wall
1. Find the studs
Drag a strong magnet slowly across the wall. It sticks to the nails that hold the lath to the studs. Outlet and switch boxes are supposed to be fixed to studs too, and most older houses are framed 16 inches on center, though old houses can vary.
2. Tape and mark
Put masking tape over each spot you plan to drill and mark the holes on the tape, so the edges of the holes do not chip.
3. Confirm the stud
Drill a small pilot hole, about 1/8 inch, where the wall plate will hide it, and confirm the stud before the big bolts go in.
4. Drill slowly
Use a carbide bit at the lowest speed, without pushing. Keep the drill straight, back it out in reverse, and wear safety glasses and a dust mask.
5. Check the bolt length
The Sanus full-motion mount we checked ships 2 3/4-inch lag bolts in 3-inch-deep pilot holes and allows drywall up to 5/8 inch over the studs. Plaster can run past 1 inch, so ask the maker whether you need longer bolts.
6. Bolt the plate to the studs
Drive the lag bolts into the center of each stud and level the plate. If the studs are in the wrong place, fix a 1/2-inch plywood board across them first and mount to the board, with bolts 1/2 inch longer.
7. Hang the TV and check it
Hang the TV, check that it is level, and look over the plaster around the plate for new cracks.
What is inside an old plaster wall
Until the 1930s or 40s, plaster was the wall surface in nearly all buildings, according to the National Park Service. The best work went on in three coats: a scratch coat and a brown coat about 3/8 inch each, then a finish coat of 1/8 inch.
Behind it is lath. Wood lath is thin strips nailed across the studs with gaps between them. Wet plaster pushed through the gaps and hardened into keys, and those keys hold the wall on.
Metal lath came into use toward the end of the 1800s. Rock lath, a gypsum board, was in use by 1900 and almost the only lath in houses by the late 1930s.
That makes a thick wall. The Park Service puts the minimum on wood lath at about 3/4 to 7/8 inch, and the Craftsman Blog puts a typical old wall at 3/4 inch to just over 1 inch, against about 1/2 inch for drywall. Not sure which wall you have? Our guide to what is behind your Chicago wall has five quick tests.
What holds a TV on plaster, and what does not
| Fastener | How it holds | On plaster |
|---|---|---|
| Lag bolts into wood studs | Threads into the stud behind the plaster and lath | The standard for a TV, as long as the bolts are long enough for the thicker wall |
| A mounting board across the studs | 1/2-inch plywood fixed to the studs, the mount bolted to the board | For when the studs do not line up with the TV. It shows unless the TV covers it |
| Toggle bolts | Wings open behind the wall | This Old House rates them at 25 to 50 pounds in plaster, and Toggler notes the hold drops as the load moves out from the wall. Not for a TV on their own |
| Plastic anchors | Expand inside the hole | May not suit plaster at all, and self-tapping ones fail in hard plaster. Not for a TV |
Why plaster cracks, and how to drill so it does not
Plaster is more brittle than drywall, and hammering a nail into it is a quick way to knock it loose from the lath. When plaster is overloaded or the house moves, the National Park Service notes, it loses its key: the bond with the lath breaks and the wall goes loose or bowed. Plaster that is already loose or bowed needs fixing first, or another wall.
So the holes are drilled, gently. Put masking tape over the spot so the edges do not chip. Use a carbide bit, set the drill to its lowest speed and let the bit cut without pushing.
Hold the drill straight and back it out in reverse. Slow drilling is what keeps cracks and crumbling away from the hole.
Wear safety glasses and a dust mask. In an older home that dust can carry lead, which has its own section below.
Old plaster, old paint: the lead question
If your home was built before 1978, the Chicago Department of Public Health says to assume the paint contains lead unless a test shows otherwise. Lead dust is too small to see or smell, and young children are the most at risk.
A few bolt holes are a small job, and the EPA's renovation rule lists drilling into plaster among small surface disruptions. It still makes dust. Catch it as you drill, and do not dry-sweep or vacuum it: the city's health department warns that both spread lead dust.
Planning something bigger, like opening the wall to run wires? The health department's advice is not to remodel or renovate until the home has been inspected for lead.
Plaster in Chicago greystones, two-flats, bungalows and courtyard buildings
Most Chicago two-flats went up between 1900 and 1920, according to the Chicago Architecture Center, and two-flats, four-flats and six-flats together make up more than 30 percent of the city's housing. The Chicago Bungalow Association dates greystones to 1890 to 1940 and the Chicago bungalow to about 1910 to the mid-1930s.
Courtyard buildings went up from 1889 to 1930. All of that is plaster country.
Most of them are brick or stone outside, so a TV on an outside wall may be going into plaster over brick, with no wood studs at all. The anchors then go into the brick, as our post on mounting a TV on brick explains.
A late bungalow may have rock lath rather than wood, since rock lath took over house plastering by the late 1930s. Whatever is behind it, our TV mounting service checks the wall before anything is drilled.
Common questions
Can you drill into plaster walls?
Yes. What cracks plaster is force: a hammered nail or a pushed drill. A carbide bit at low speed, with masking tape over the spot to keep the edges from chipping, makes a clean hole. Wear glasses and a dust mask.
Do stud finders work on plaster walls?
Not reliably on plaster and lath. A strong magnet does better, because it finds the nails that fix the lath to each stud. From one stud, the next is usually 16 inches away in an older house, though old houses vary.
How do you mount a TV on plaster without a stud where you want it?
Fix a board of 1/2-inch plywood across the studs and bolt the mount to the board, so the TV can sit anywhere along its width. Toggle bolts alone are not enough: This Old House rates them at 25 to 50 pounds in plaster, and Toggler notes they hold less the farther the load sits from the wall. On plaster over brick, anchor into the brick.
What is lath and plaster made of?
Lath is the backing: thin strips of wood with gaps between them, or later metal mesh or gypsum board. Plaster went over it in coats, a 1/8-inch finish over two base coats of about 3/8 inch in the best work. Old lime plaster was mixed with cattle or hog hair to hold it together.
Can a full-motion mount go on a plaster wall?
Yes, when it is bolted into wood studs. An arm pulls harder on the wall the farther it reaches out, and one full-motion mount's manual asks for a wall that can carry five times the weight of the TV and mount together. Toggle bolts in plaster are not that wall.
- #Plaster walls
- #Chicago homes
- #Wall anchors
