I have a rewire to do in a couple of weeks and the house has plaster walls and ceilings. The AHJ tells me that I will have to add recepts where they currently are not and that means a lot of new holes. I need to know of a good way to cut these holes without cracking the plaster . I don't think that a sawsall would be very gental but a keyhole won't work either. Any ideas? Chris
Chris: FWIW, I used a small angle grinder (DeWalt) with a diamond cutting blade. Tool (rebuilt, factory store) and blade was around $100. Trick is to bring your patience with you, and remember under the plaster is wood lath, or the dreaded black diamond wire mesh. Plaster of paris for patching works great. A sawzall vibrates everything, the DeWalt works like a circular saw.
Try using a milwaukee keyhole saw that excepts sawsall blades. I use this all the time . Then I put a 24tooth hacksaw blade in and cut the lath. BNe sure to only cut away 1 full strip of lath and have the top and bottom land on the remaining partially cut pieces. Depending on the plaster you may or may not need to patch. Oh you will have to use a scewchissel to break out the plaster first. (screwchissel is an old scewdriver now used as a chisel, and sometimes can become a screwawl) This is not a slam bang operation it is a time consuming and you will need patience.
Patience is the Key. With working with Plaster, I make a starter small hole in the middle of the Box, Hi Hat, and it seems like a crack travels to that point. Then you could chip out the rest without sweating too much. Good Luck
This is pretty much what the Roto-zip was made for.
I have to 2nd this one. A Rotozip is great for this and it will work on the diamond wire mesh with the right bit. They also sell an attachment for a shopvac to keep the dust to a minimium. Once you get the hang of it you can make clean and accurate holes that hold a remodel box nice and tight. Making the job look that much better.
I usually use a hand jigsaw to cut the lath. Works great if it's soft wood. Never had to cut holes for boxes so far though, only conduit penetrations (that means you can just chip away some plaster, cut the lath, fish the flex conduit and plaster around it). One trick I read: scroe the plaster with an old knife to get an even line.