I have a number of ~3" holes in my plaster from where my walls were filled with insulation. (Why did they drill a 3" hole? I have no idea).
Obviously I would like to fill these holes in, but they have no lathing behind them, and I'm not sure what is the best way to fill them in is.
Here is what the holes look like:
This question is very similar to this question:
How Do I Fix a Hole In Drywall
There are some good answers posted, so it is worth a read.
To build on those answers for this particular case, I would recommend the medium size hole fix. The only difference is since the hole is on the small side, trying to screw the new 3" circular piece may crack or break it in half or in pieces, so my recommendation is to glue it to the strapping or backing material using gorilla glue or similar. Just make sure the new piece doesn't stick out of the existing wall. If you can make it slightly less than the existing wall, that would be optimal, and then you can just fill in the depression with mud/spackle.
If the plaster is painted, you can use mud to fill in, it doesn't have to be plaster as the paint will cover it over. If it is unfinished plaster, then fill in with plaster as the finish will be the same. It looks to be painted, so standard mud/spackle should work out fine.
Lath and plaster openings can be repaired without the typical crack at the perimeter that is usually a result of inexperienced repairs. Lath and plaster consists of plaster board and plaster applied over the board. Take a hammer and chisel and carefully chip the old plaster off the board behind it; leaving at least 1" of exposed board around the perimeter of the opening. Cut a piece of expanded metal lath to fit over the entire opening and slowly screw it onto the board using short drywall screws. Apply a thin coat of quick patch plaster over the metal lath and allow to set. Apply a second coat of quick patch plaster to completely fill the hole and shave the surface flush to the surrounding wall using the edge of a trowel; (perpendicular to the wall). Clean excess plaster film from the surrounding wall. Allow the second coat to harden, then mix a little more plaster in a very wet form, (almost like paint), and apply tightly over the patch. Allow to set .. then mist the patch with water and trowel smooth using a little pressure as you do it. The result should be smooth and it will not crack.
I follow insulation companies that leave behind holes just like this. I add a 7inch wood lath with drywall screws. Then put back in the sheet rock cut out or I cut my own 3inch circles. Tape and plaster. Come back next day to sand. then texture if they need it.... I do this as a living
Either go to your hardware store and they sell patch kits or cut out a strip in your sheet rock wall from stud to stud and get a piece of sheet rock, make sure its the same thickness so measure it be for you go to the hardware store and cut the same size you cut from your wall and nail it to the studs, plaster/mud over the cut marks, retexture and paint and your done, I know it sounds like a lot of work but its actually pretty easy.
Use a small strip of 1/4 inch plywood as backing, insert it into the hole and screw in place with drywall screws. It doesn't have to fill the hole completely. Then fill the hole with setting type joint compound with 90 mins set time. When mixing the mud with water, add some concrete adhesive to it.
