I had a leak that has been fixed, but I now need to take down the ceiling plaster to replace it. How do I fix a 7"x7" across, and 1/2" deep hole in the ceiling?
You question doesn't really say what type of ceiling you have so I am assuming regular drywall although you did say plaster.
If possible, check the space in the attic above the damaged area for wires or plumbing lines. Use a stud sensor to locate the ceiling joists and determine what direction they are facing.
Poke an awl through the ceiling around the damaged area to determine how far the damage extends.
Use a straight edge to mark the area you plan to remove, and use a drywall saw to remove the damaged area and any insulation from above.
Most ceilings use standard 5/8-inch drywall; however, drywall is available in different thicknesses. Your replacement piece should be the same thickness as the existing drywall.
Make sure the replacement piece will have adequate support. If necessary, you can toenail a wood block between the joists for added support.
Use a utility knife to cut out a piece of drywall to fit the area you're replacing.
Replace any insulation you removed earlier, and fit the replacement piece into the hole in the ceiling. Secure the drywall to the ceiling joists using drywall screws. The screws should just dimple the drywall rather than breaking all the way through the surface.
Apply a thin layer of joint compound over the joints and drywall screws, and apply a piece of drywall tape to the wet joint compound. Apply an additional layer of joint compound over the drywall tape and smooth it out with a drywall knife.
Sand the area smooth and apply additional coats as necessary. Sand between each coat.
When the area is dry and smooth, prime and paint it to match the ceiling.
My house is 110 years old. I have lath underneath the plaster. Wouldn't the preceedure be done differently?
You would need to inspect the lath to make sure it was secure to the rafters, if there are any lose boards you will need to secure them in place.
Spray any exposed lath or other holes with water, then apply plaster patching compound using a putty knife to bring holes smooth and even with the rest of the ceiling. Wait for the compound to dry completely, then sand the section smooth using 100-grit sandpaper.
Cover the patched section with a layer of self-adhesive fiberglass mesh tape. Coat the mesh tape with joint compound, then allow it to dry. Add a second coat to smooth out the patched area and the washers, creating an even, level surface. When the joint compound dries, sand it smooth with 100-grit sandpaper, then prime and paint as needed.
Can you use spackle in place of compound?
You sure can, Spackle doesn't shrink or crack as it dries as do most drywall compounds if applied too heavily.