How do I install a receptacle box in lath/plaster wall?

Question

I have a room with ungrounded electrical receptacles and I need to install a grounded outlet. The walls are lath and plaster. What I want to do is install a new receptacle box for the outlet. Is there a way to do this without having a big hole to repair? Basically I'd just like to cut a hole just big enough for the receptacle box, but not sure if it's possible.

I can easily get a wire to the desired location. I'm just not sure of how to get a receptacle box into the wall. There is a stud at the spot for an attachment point.

Any links to a site with pictures or diagrams would be a real plus.

Answer 1

I think you would be better off using a remodeling box (with the flanges that rotate out to grip the wall) and ignore the stud altogether. With a remodeling box, you just have to cut a hole big enough for the box, whereas if you use a regular box, you have to cut away more so you have room to nail it into the stud.

The main difficulties you'll face are that you don't know exactly where the lath is placed within the wall, and that the plaster will be brittle with age.

Start by using something sharp to gouge out a small hole in the center of the spot for your new receptacle; I use the pointed tip of a drywall saw. Once you've exposed the lath, expand the hole up and down until you find the edges of that piece of lath. The other lath are going to be approximately the same size and spaced up to maybe 1/4" apart. Adjust your planned spot up or down a little so that at least one edge of the box lines up with a gap in the lath -- it's easier to cut through the plaster on its own.

Expand the hole until it's big enough for the box, then use a jigsaw to cut away the lath. Vibration from the saw can cause more damage to the wall so take it very slow and easy. (Another reason to avoid the stud: if the lath ends at that stud, you'll only have about 1/2" of it to hold the plaster in place.)

Answer 2

Probably the least damaging way of adding a hole in lathe and plaster for a new receptacle would be to use an oscillating tool with a cutting attachment. Right now you can get one at a Harbor freight for really cheap. Just make sure to get a good quality cutting attachment that will get you through the project.

If your walls aren't too thick, you can use an "old work" electrical box to avoid having to screw in the plaster, which has wings on the back that fold out and suck the box to the wall when screwed in.

Unfortunately, its not very easy to know where studs are behind lathe and plaster, so if you make your hole right over the center of a stud, you'll probably have to move your hole over and repair the wall to the side of your new outlet. If that happens, you can likely just screw a small piece of drywall onto the stud and mud over it.

Best of luck!

Answer 3

You might consider the smaller "metal outlet boxes" that are mounted as "old work" using "madison straps". The advantage is that (at least some of) the metal boxes are smaller than the plastic boxes so you have a larger margin between your box hole and the outer dimensions of your outlet plate so that more damage to the surrounding plaster can be concealed by the plate. I also find the madison straps easier to install securely when the wall is thick, as is the case with plaster and lathe. For examples just do an image search on the quoted text above.

Answer 4

I did something similar, and my wall is lathe-and-plaster, but covered with drywall. I started by drilling a hole with a hole saw, then extended the hole to the size of a receptacle box using an electric jigsaw. A bit of dust, but it worked wonderfully; it was not hard to make the hole the right size and shape.

I don't know if it would be different if there were no drywall. Perhaps I would have to worry about the plaster chipping around the edges?

I also discovered that I needed to use a shallow receptacle box, for there was not enough space inside the wall for a regular one.

Answer 5

A high-speed 4" grinder works best. It does not damage the integrity of the plaster wall. Of course you will have to finish the corners of the cut out with a reciprocating saw.