Fishing New Cable Through Plaster Walls

Rewiring an old house doesn’t have to mean gutting it. With patience, a few tools, and access from the basement and attic, you can run new cable to many outlets and switches through holes the size of the box you’re installing. The secret is understanding how your house is framed.

Why balloon frames help

Many houses built around 1900 were balloon framed. In a balloon frame, the wall studs run in one piece from the sill on the foundation all the way up past the second floor, and the second-floor joists rest on a 1-by-4 ribbon let into the studs rather than on top of a first-floor wall ¹. The result is that each space between studs, each stud bay, can be an open channel from the basement to the attic.

That’s a fire hazard, which is why building codes later required fire stops: 2-by-4 blocks nailed between the studs to close those passages ¹. Your house may have them in some bays and not others, or at the second-floor line where the joists come in. When you’re fishing cable, a blocked bay means drilling through the block or opening the plaster to get past it.

(Platform-framed houses build each floor as a separate box with plates at every level, so fishing there means drilling through plates from above or below.)

Plan the route

• Outlets on the first floor: come up from the basement. Find the bay from below, drill up through the sill or bottom plate, and push a fish tape or flexible rod up to the outlet hole.
• Switches and ceiling lights on the second floor: come down from the attic, drilling through the top plate.
• Across a room: run through the basement or attic, never diagonally through a finished wall.

Measure carefully from a fixed reference both inside and below (a window, a pipe, a corner) to match the hole in the basement to the bay you want. A small test hole behind where the box will go confirms it.

Cutting into plaster

Plaster is not drywall. On thick plaster, stud finders often fail; knocking along the wall and listening for the hollow sound works surprisingly well, and a small test hole that will be hidden by the box settles it ². To cut the opening, trace the box, then drill a row of closely spaced holes around the outline and chip out between them rather than hammering or sawing hard ².

Houses with wood lath, generally the older ones, need the most care: the plaster is fragile and tends to break away from the lath when you work on it. Matthias Wandel, who has rewired an older house himself, suggests that in wood-lath houses a box mounted near a joist or stud may be the better choice ². Use old-work boxes, whose ears or clamps grip the back of the wall, or screw the box to a stud ².

Pulling the cable

• Use a steel fish tape or fiberglass fish rods, and pull slowly; cable insulation scrapes easily on rough lath and old nails.
• Leave plenty of extra length at each box.
• Keep standard practices: the right cable gauge for the breaker, one wire per terminal, and a continuous ground ³.
• Mark every cable at both ends before you pull.

When you’re done, fill the drilled test holes and chipped edges with plaster patch and paint ². And for every abandoned old circuit, make sure it’s dead and disconnected at its source.

Try it

Pick one outlet you want to add on the first floor. From the room, measure its distance from the nearest corner or window. Go to the basement and find that spot under the floor. Is there a clear path into the wall bay above, or a sill, block, or duct in the way? Sketch your route before you buy any cable.