What are good ways to cut through rock lath and associated plaster (to install new Jboxes for outlets)?
Rock lath/skim plaster can be cut with a rotary cutter (rotozip). Older wooden lath and brown/white plaster layers do well with a oscillating cutter such as the Fein or one of the copycats.
Thanks, the latter is what I have. I don't know too much about power tools so I will have to look into it.
OK, I looked into it. It turns out that I bought what looks like a Fein clone a few weeks ago to cut into some walls in my garage. If it is not too much to ask, maybe someone could advise me about what type blade or attachment I should use for the rock lath.plaster. I have no experience with this tool beyond cutting off some think plywood. I wish I had some of what I am cutting to practice on before I hit the real wall!
The "rock lathe" is just gypsum panels.
It cuts fine with a coarse plaster cutting blade on a Sawzall.
Buy plenty of blades, the sand in the float layer (second on a three coat, first on a 2-coat on rock lath) takes the edges off the blades very quickly.
With some practice you can even start a cut 'blind' without a starting hole.
If you keep the blade almost parallel to the wall surface it can even cut wood lathe with minimal collateral damage.
If you use almost any type of reciprocating cutter perpendicular to wood lath it tends to break off the 'keys' holding the base coat to the lathe and weaken the plaster wall greatly.
"If you use almost any type of reciprocating cutter perpendicular to wood lath it tends to break off the 'keys' holding the base coat to the lathe and weaken the plaster wall greatly."
That should be true for the rock lath as well. Looking at the back side of my rock lath though, it seems like the potential for forming keys is not as high as for wood lath so maybe there is more dependence on the plaster sticking to the sheet than with the older wood lath system.
I do have an oscillating cutter, but I don't have a Sawzall.
"That should be true for the rock lath as well."
Not nearly as much.
There are no keys with rock lathe except at joints between the panels, and those are not keys so much as just filler.
The face of the material i not papered but bare gypsum designed for plaster to stick without any help.
Rock lathe is a 2 coat plaster system, as opposed to 3 coats used on wood or expanded metal lathe.
I have removed large sections of rock lathe, installed wiring, plumbing, even pocket doors, then put the large pieces back up and repaired the joints created.
I even turned the studs on the other wall section to lay flat, screwed the plaster to thee new studs, then installed flat studs on the second side and used the pieces to repair the wall, leaving a nice pocket with a header for the pocket door.
It results in a much more solid wall around the pocket that can support 4x4 1.25 inch deep electrical boxes with minimal loss in floor space.