plasterwiring
Most of my walls consist of solid plaster over masonry, which makes electrical work difficult to say the least. I want to add some wiring to an existing wall in order to add light fixtures to a room which currently lacks them. Since there are no stud bays to run wires, I will need to cut channels in the plaster to run armored cable or conduit.
What are the best tools and techniques for accomplishing this?
If wallpaper was painted over you could tell pretty easily by pulling on some of the peeling paint and breaking the paint chips. Wear a respirator mask while doing this, however, as often times flaking paint is a potential indicator of lead based paint. If the chips contain paper, then you're right, it's wallpaper with paint over it. If it's just paint, then be more careful - get the chips tested for lead.
Given the wide spread flaking, it is likely that the wall simply wasn't properly primed. An improperly treated wall when painted over will eventually lose adhesion with the paint and it'll flake away like you're seeing. If they applied paint directly to wall paper w/o priming, I think the same is true.
That 2nd picture DOES remind me of wallpaper... I've scrubbed far too much backing off the walls and that looks similar.
The grey subsurface is, I think, a kind of stucco mix that was often used to even up walls where lathe and plaster was replaced with the older style 2x4 drywall panels. It's nasty, gritty, dusty, unpleasant stuff, tougher than joint compound/plaster to work with because of it's tendency to crack and break rather catastrophically. When I run into that stuff in my rentals my approach is, "IF I have to touch it at all, it's ALL coming down." Plus with wallpaper I swear gutting is easier than stripping.
Now around the vent pipe, that looks like moisture damage. The bubbling around the pipe suggest water leakage. Is that a "finished" ceiling - ie - thats the roof on the other side of that wall w/ the pipe? If so, make sure it's properly sealed and replace at least that area of ceiling. Picture #5 seems to confirm this - someone touched it, and patched it badly.
I agree with @DA01 that it'll basically be impossible to fish horizontally through studs and insulation, without having to cut open all of the sheetrock. Then you have to deal with sealing it all back up air-tight, and patching the drywall and repainting (at least the entire wall, and maybe the entire room, depending the paint match).
So a couple alternatives:
Use a wiremold type product to surface mount the conduit:
There are lots of different brands, and it can be paintable. With planning, you can minimize where you see it.
Build up the wall using cabinets or a false wall, so you can run wire in behind, on top of the existing wall.
Could be as simple as just a drywall section sticking out, or some built-in cabinets or some brick work. Cabinets of course have the benefit of being able to build in other components such as your A/V gear and speakers.
Best Answer
Channelling chisel on SDS drill.
For short runs a brick bolster works reasonably well (and produces much less dust)
Deeply scoring the plaster with a knife beforehand to define the edges of the channel may help to prevent large irregular chunks being removed.