Restoring plaster walls and ceilings is a lost art. All too often, so-called professionals will perform short-lived repairs, using a simple mix of plaster and joint compound that will look good at first but will not last. Proper restoration can be achieved by following the plaster restoration steps herein.
Removal the damaged plaster. This is a dirty job so be sure to cover the area thoroughly. It is advisable to drape plastic over any open doorways to contain the mess to the room being restored. As large plaster chucks are heavy, it is also advisable to place blankets over any furniture that can't be removed from the room as well as hardwood floors. Use the hammer and stiff scraper to remove loose plaster, including the brown coat, which is the layer beneath the plaster that looks like cement. Continue working out from the center of the "hole" until the plaster is firm. Do this for all the damaged areas in the room.
Clean up the room! At this point, it will be very helpful to completely remove all the damaged plaster from the room, shake your drop cloths and reset the room.
Use the vacuum to thoroughly clean the spots to be repaired. This is very important. Once completely vacuumed, use the sponge to clean the spots. There will be "lathing" beneath the brown coat, which is where the first coat will "grab", which must also be sponged clean of dust. The lathing will either be wood strips, wire mesh, or lath board, which looks like sheetrock with evenly spaced holes in it, depending on when the structure was built.
Apply the bonding solution to the areas to be repaired. Use any concrete/cement bonding solution to do the job, and this can be found at virtually any hardware store. This step is so often skipped and it is very important. Allow to dry in accordance with the directions on the label of the product being used.
Apply the perolated plaster coat next using the plaster trowel. Perolated plaster will also be available at any hardware store.This coat takes the place of the original brown coat and makes all the difference for a lasting repair. Mix in accordance with the ratio indicated on the product label. "Push" the plaster into the area to be repaired, working from the edges to the center. The "push" will force the plaster into the lathing and ensure a firm substrate for the following coats. Do not fill up to the grade of the original wall surface. Leave it about 1/8-inch below grade so there is room for the next coat. Scrape any excess from the wall area surrounding the repair and clean using the sponge. Allow to dry for at least 24 hours.
Apply the "scratch coat" which is a mix of plaster and spackle or joint compound, about 2 parts plaster to 1 part compound. This is a little tricky because it dries quite fast and remains workable for a very short time. Mix small amounts at a time. Apply from the center outward, applying enough pressure on the trowel to work the plaster into the substrate and edges. This coat should be brought even with the grade of the existing surface. Again, scrape off the excess from the existing wall area and sponge clean. Allow to dry for at least 24 hours.
Use the medium sandpaper to sand any rough or high spots. Sponge the area clean.
The "cream coat" is now applied using the joint compound or spackle and the taping knives. A 10-inch knife will work the best. This is a very thin coat that extends about a foot past the edges of your repaired areas in all directions. Allow to dry and use the fine sandpaper to sand the entire area. Many times, a second or "polish" coat will be required to achieve the best finish.