Old style plaster walls are created by spreading plaster over strips of wood that are nailed to the studs horizontally. Those strips are called lath. The plaster oozes through the spaces between the lath and dries to form “keys” which holds the plaster to the wall. In this video, I show you how to add new electrical work to old plaster walls by channeling plaster to reach the lath.
Busy as a Beaver
The channels cut through to the lath are just like the network of tunnels dug by groundhogs or beavers. They create a place to lay the BX armored cable.
Score the wall where you will be channeling plaster. This will cut through the layers of paint on the walls. Then chip away the plaster between the scored lines down to the lath using a hammer and chisel.
Once you’ve created the channel, cut away the lath to pass the cable between studs or to create a hole to place an electrical box. Secure the cable to the lath with screws, bent nails or cable clips.
Just Like Frosting a Cake
Once your cable has been laid, the next step is to cover it over again with new plaster. Fill larger holes with something called Structo-lite. This rougher, stronger base coat plaster holds the new electrical work in place. Smooth it over with a top coat (or three), after the Structo-lite has dried.
Have the walls tested for asbestos before beginning the work. You’ll need to have it professionally abated before you can do any work installing new electrical.
Once you have the all-clear on asbestos you can go ahead and channel your walls. It’s important to wear a breathing mask. Old plaster was frequently mixed with horsehair to help bind it together, and that old bio-matter can contain microorganisms that could be reanimated with moisture.
Only use the armored, or metal wrapped cable. Do not use romex, or plastic wrapped cable. Nailing through a wall to hang a picture, you can puncture the romex and expose the wire, which can create a fire hazard. Armored cable is more resistant to nails and screws.
Channeling plaster is a big project to undertake, but it’s not out of the question for a weekend warrior. Plan out your project well, and be prepared for a holy mess!