Figure out which wall you have
You'll usually find one of three walls, and each takes different hardware.
- Drywall over studs. Common in newer houses, additions and renovated rooms. The studs carry the load; the half-inch panel between them does not.
- Plaster on lath. The National Park Service's Preservation Brief 21 describes three kinds of lath behind old plaster: wood strips, expanded metal, and rock lath (gypsum board lath, in use by about 1900 and common by the late 1930s). It gives the minimum plaster thickness over wood lath as about 3/4 to 7/8 inch, so the stud sits deeper than it would behind drywall. Ask whether the screws that came with the mount are long enough to reach solid wood.
- Plaster directly on brick. The same brief notes that plaster was often applied straight to masonry with no lath. In a rowhouse, the city's Rowhouse Manual says party walls in older homes are usually brick, two or more layers thick, and some carry the floors and roof. A TV on the wall you share with a neighbor is going into brick, which needs masonry anchors, not wood screws or drywall anchors.
The party wall also limits what you can cut. The manual says openings in party walls should be filled to keep the fire separation intact, and that any change reducing a party wall's strength needs an architect or engineer. A few anchor holes are a normal installation; a recessed TV box or a cable run cut through to the neighbor's side is a different project.
Match the attachment to the load
For a flat-screen, PNNL's guide to anchoring appliances and electronics says to put the mount's screws into studs, or to attach horizontal 1x4 boards to at least two studs and screw the mount to those boards. That second method helps when the TV needs to sit between studs.
The same guide explains the VESA pattern, the spacing in millimeters between the four holes on the back of a TV. Sizes run from 75 x 75 to 800 x 600, and 200 x 200, 400 x 400 and 600 x 400 are common. Find yours in the TV's manual or measure it, along with the TV's weight, before you buy a mount, and check that the mount is listed for both.
For shelves, count what will sit on them, not just the empty boards. For freestanding bookcases, PNNL says to use L brackets screwed into studs and into the top or sides of the unit, never into the thin back panel. If children live in the house, CPSC's Anchor It guidance says flat-screen TVs should be mounted to the wall or to furniture, and TVs that aren't wall-mounted should still be anchored.
Check the plaster before trusting it
Old plaster holds on through "keys", the bits that squeezed through the lath when it was wet. Preservation Brief 21 says moisture, rotting lath, rusted nails or poor-quality plaster can break those keys and leave plaster loose. Before mounting, look and press lightly around the spot. A bulge, a section that flexes, a damp stain, or a crack that runs along a ceiling or wall corner deserves attention first. The brief says hairline cracks in an otherwise sound wall can simply be filled, but cracks where walls meet may be structural and should be investigated. Loose plaster can often be reattached with screws and plaster washers before anything heavy goes on it. Our guide to cracks that keep coming back above doors and windows covers what recurring cracks can mean.
Wiring, pipes and old paint
Treat the wall straight above and below an outlet or switch, and the wall behind a sink, toilet or tub, as likely cable or pipe routes, and pick another spot when you can. If you want a new outlet behind the TV, that's electrical work, not mounting; in Philadelphia it may need a permit, which our L&I electrical permit guide explains.
In a house built before 1978, drilling into painted plaster makes dust that can contain lead. Read what to check before sanding or scraping paint in a pre-1978 home before the drill comes out.
What to ask the installer
- What is behind this spot, and how did you confirm it?
- Will the screws go into studs, backing tied to at least two studs, or brick, and does the mount's manual allow that fastener?
- Is the mount listed for my TV's weight and VESA pattern?
- If the plaster here is loose or cracked, will you secure it before mounting?
- Are you running any wires inside the wall, and do I need an electrician or a permit for that?
A carpenter or handyman who regularly works on plaster is the right call for most mounts. Bring in a mason for heavy loads on brick, an electrician for new power, and an engineer if the party wall is cracked or bulging.