Homes that still have plaster walls in prime condition are often valued by homeowners and home buyers alike. Not only are they beautiful and solid but they are especially good at soundproofing rooms. But plaster walls respond to inevitable foundation shifts and climatic changes and can begin to crack. Everyday life, with its bumps and bangs, also takes its toll on plaster walls. And certain key areas, such as above and beside doorways and windows, are classic areas of cracking. Nearly all homes with plaster walls will eventually develop window and door cracks.
Though they may look scary, your cracked plaster walls are not beyond repair. You do not even need a special plaster repair kit. One way to quickly fix cracked plaster walls involves basic drywall tools and materials that you can buy at any home improvement store.
Plaster vs. Drywall Repairs
Understanding how plaster walls are constructed will help you fix your cracked plaster wall. The process is different for plaster than for drywall. If you have ever repaired drywall, you may know that it is often easier to replace entire portions with new pieces of drywall—it's possible to remove just the section that needs fixing and a few inches beyond, without the entire wall collapsing. Because drywall is one layer with no backing, once you cut through drywall, there is nothing behind it except for studs and insulation.
Plaster walls, by contrast, are constructed of two layers: the outer plaster and the inner wooden or metal lath. With plaster, your best bet is to preserve the existing plaster and to fix it, rather than tearing it out. Ripping out chunks of plaster often becomes a seemingly endless process, with one chunk leading to another chunk. Successful plaster crack repair requires taking it slow and being patient enough to add multiple layers of drywall joint compound to the wall.
Equipment / Tools
- Utility knife or 5-in-1 tool
- Shop vacuum
- 6-inch drywall knife
- 12-inch drywall knife (optional)
- Drywall joint compound
- Paper drywall tape
- 150-grit sanding sponge
Score the Crack
Use a utility knife or painter's 5-in-1 tool to cut along the edges of the crack, opening up the crack slightly and removing loose material. While opening the crack may seem counterintuitive, you need to increase the area for the joint compound to stick. Do not vigorously scrape into the crack; be gentle and go slow. Use a shop vacuum to remove all crumbs and dust from the crack.
Cut the Paper Drywall Tape
Measure and cut one or more lengths of paper drywall tape to fit the crack. Drywall compound begins to dry quickly, so cutting the tape in advance makes this work go faster and prevents accidentally creating creases, folds, or bumps. Use scissors or a utility knife to cut the tape, as tearing the tape by hand will produce a ragged edge.
Spread the Joint Compound
Mix the drywall joint compound, as needed. Scoop up a small portion with a 6-inch drywall knife, and smooth a thin layer of joint compound over the crack, making a path that's a little wider than the paper tape. Move immediately to the next step, as joint compound dries rapidly.
You can use premixed "all-purpose" mud or compound sold as a dry power that you mix just before application. Premixed is more convenient but usually has to dry overnight. Powdered mud is harder (especially "setting" mud) and can dry in as little as 20 to 90 minutes, depending on the type.
Apply Tape to the Crack
Lay the tape onto the mud by hand, then smooth it with the 6-inch knife with one or two passes. The goal is to flatten the tape and ensure full contact with the compound, with no wrinkles or air pockets. Be careful not to overwork the tape and tear it. Let the joint compound dry completely.
Mud Over the Tape
Add a layer of joint compound over the taped area so that the compound extends past the tape's edges, using the 6-inch knife. Smooth the compound so it is flush with the surrounding surfaces. Let the joint compound dry completely.
Sand the Repair
Lightly sand the compound with a 150-grit sanding sponge or sandpaper to smooth prominent bumps or ridges. Do not sand so hard that you expose the tape.
Apply an Additional Mud Coat (optional)
Add a third layer of joint compound, this time using the 12-inch knife, to extend the edges even farther. This is an optional step that helps blend the repair into a very smooth wall surface. If the surface has some texture, it's usually better to take the opposite approach and minimize the width of the repair, since it's hard to texture the new compound.
An additional coat should take the joint compound out as far as 12 inches. Allow the joint compound to dry completely, then sand lightly to smooth out the repair area. Again, take care not to sand down into the paper tape—a very light sanding is all that is required.
Clean the Area
Clean the patch and surrounding area with a shop vacuum and wipe it with a dry cloth.
If the wall or ceiling has a heavy texture, you can try to match it by spraying over the patch with an aerosol spray texture in a can. You can also replicate hand-applied plaster textures using drywall compound and various texturing tools, such as a whisk broom or a sponge. Always prime new joint compound or texture before painting.