Project example: a 55-inch TV on a plaster-over-lath wall beside a built-in bookcase in a period home — what it looks like and what it costs

The scenario

The room is the living room of a one-story house from the 1920s: arched doorway to the dining room, a tiled fireplace on the long wall, and on the short wall a built-in bookcase with glass doors that the household would not touch for any price. A deep-green sofa faces the fireplace and a pair of windows lets in morning light from the side.

The request is a 55-inch TV that can be seen from the sofa without hanging over the fireplace and without cutting into the bookcase. The only free wall is the short one, beside the built-in, and it is plaster over wood lath with a picture rail near the ceiling.

Two details shape the plan. The plaster is thick and the lath hides the studs from the finder, so the stud edges have to be proven by hand. And the nearest outlet is on the opposite side of the bookcase, so the cable cannot take the short way without crossing the woodwork.

What the job involves

1. The installer tapes the screen outline on the plaster, sits on the sofa and moves it until the center sits near the seated eye line.
2. A stud finder gives a first guess; a small probe hole under the future plate proves the stud edge, and the hole will be covered by the plate.
3. Painter's tape goes over each drill spot, and a carbide bit at low speed with the hammer off makes the pilot holes through plaster and lath into the stud.
4. Long lag bolts are driven into the stud centers; the plate is leveled before the last turn so it does not pull the plaster.
5. Two people lift the set onto the plate; the lock screws go in and the bubble is read again under load.
6. A slim raceway painted to match the wall follows the picture rail and runs down to the outlet beside the window, leaving the bookcase untouched.

Hardware and materials

• Fixed or slim tilting mount rated above the TV's weight
• Lag bolts long enough to pass plaster and lath and bite deep into the stud
• Carbide bit, drill-driver, stud finder, laser level
• Paintable raceway kit and a small can of matching paint left to the owner
• Corner guards for the doorway and a small vacuum for plaster dust

Add-ons often paired with this job

• Hide the wires inside the wall — +$90–$150. In-wall concealment is not suggested in this plaster wall; the raceway is the usual route.
• Mount a soundbar as well — +$50–$80. A bar on its own bracket below the TV, fixed into the same studs.
• Take down an existing TV first — +$40–$80. An older TV on another wall is taken down and the holes left for the owner to patch, as a separate line.

Why it is done this way

Plaster over lath is not harder to mount on than drywall, but it punishes haste. A fast bit chips the finish, and a bolt that stops in the lath instead of the stud holds nothing. The probe hole and the slow bit are what the extra money pays for.

The raceway keeps the work small and reversible: nothing is cut out of the plaster or the woodwork, and the line follows an existing edge of the room so the eye reads it as trim. The built-in stays as it was, and so does the fireplace.

The plaster add in the estimator covers the longer bolts and the slower drilling, which is why the example sits above the plain-drywall range for the same TV.

What would change the price

• The studs sit in a different place and the plate moves along the wall.
• The wall turns out to be a mix of plaster and a later drywall patch, each with its own fastener.
• The owner prefers an in-wall route and an electrician is brought in for the outlet.
• A 65-inch set in place of the 55 would keep the same wall add; only the plate width changes.