I need to fill a tall narrow gap in a plaster wall as shown in the image below. My question is: what is the best way to repair this? I have cut some ~1 pieces of drywall to fill the gap then tape the gaps from the drywall to the plaster however, I have been having a hard time cutting such thin pieces of drywall without it falling apart. Is there a better way to do this? the distance is about 8' from floor to ceiling.
Since it's too small to fit a piece of drywall, I would fill the gap with setting-type joint compound embedded with fiberglass mesh. It may take two or three coats to fill the gap. After it's filled, finish the two sides like you would if it were filled with a piece of drywall: Tape the patch with paper and feather out to the plaster. Then put on a finish coat of compound. Many folks prefer to use the pre-mixed stuff to finish, but you can use the setting type you used to fill the gap.
I'd use a combination of wood and wire lathe, bringing the new wire lathe out flush with the old wire lathe. Wire brush out all of the loose pieces, then fill it in with a green coat of STRUCTO-LITE plaster, followed by a coat of Durabond setting type 90, then finish off with a coat or two of Light Weight setting type 90.
"WET" the joint with a spray bottle, before each plaster coat.
Use the wide "blue" fiberglass tape, on the seams of the joint, any time after the plaster coats.
Keep the Durabond coats thin, just enough to smooth the surface - plan on sanding the top coat, NOT this coat.
