A crack or a hole in a wall can be the result of numerous forms of abuse: a doorknob banging the back of the wall; a misguided hammer; a water leak in the ceiling or wall.
While it’s fairly easy to make imperfections in walls, it’s a lot tougher to repair them.
“Compared to painting, patching a wall is a very tricky job,” says Walt Gozdan, technical director of the Rohm and Haas Paint Quality Institute in Spring House, Pa. The institute is the educational and testing arm of Rohm and Haas, a supplier of paint materials.
“If you’re prepping a wall prior to painting it, you’ll need a lot of patience and elbow grease to get that wall to look smooth and flush,” says Keil Morek, a sales associate at the southwest suburban-based Southtown Paint and Wallpaper. “It’s a slow and often dusty job.”
Complicating this situation is the big difference between working with plaster walls versus wallboard walls.
Plaster walls, which were used mostly on homes built before World War II, are thicker than drywall. The plaster is affixed to laths-narrow, thin pieces of wood that run from stud to stud.
Wallboard or drywall walls, on the other hand, are 4-by-8-foot preformed sheets of a plaster-like material that’s usually 1/2 inch thick or less. The sheets are cut and nailed or screwed to the wall studs and the gap between sheets of drywall is then covered with pieces of tape and a drywall compound.
Wallboard is found in most homes built after World War II and in most new additions to older homes.
The way to determine what type of wall you have is simply to look for laths in any holes in the wall.
“Overall, it’s easier for the do-it-yourselfer to do wallboard repair, in that plaster requires a bit of technique,” says Gozdan. “You’re using mostly a loose plaster to repair plaster walls while wallboard wall can be repaired with solid pieces of drywall.”
Of course, before making any wall repairs, be sure to eliminate the source of the hole, whether it’s a leak or a missing doorstop.
“Planning is also important. Either plaster or drywall repairs may take several days to complete,” says Morek. “So give yourself enough time to make repairs before painting walls.”
Here are some tips from experts on repairing damaged plaster:
Plaster repair
Cracks: Plaster cracks usually are fairly easy to repair. If it’s a superficial crack, dampen the crack slightly with a mister and patch it with drywall compound, using a wide wallboard or putty knife to fill in the gap.
Deeper cracks will require more effort. Check the crack for deteriorating plaster, removing anything that feels spongy or loose. Then thoroughly clean the gap. If the crack becomes wider than 1/4 inch, use fiberglass mesh tape to fill it in. Fill the crack with drywall compound, then anchor the tape in the compound.
Cover the tape with additional compound, feathering the edges of the patch. “With plaster, the key is to feather the fill as best as you can for a smooth look,” says Morek.
To repair bulges around cracks, you’ll need to chip away at the sagging plaster, again widening the crack. Again, you can use fiberglass mesh tape and wallboard compound to fill in the crack.
Small holes: If the laths in the hole are in good shape, you can simply apply a coat of replacement plaster in the gap. Remove any loose plaster, scrape the edges of the hole with a utility knife and then dampen the hole with a mister.
Mix the plaster to a very thick consistency and apply it firmly into the laths. As it begins to harden, scratch a criss-cross pattern into the plaster to help the second coat adhere (this is known as “the scratch coat”). After the plaster completely hardens the next day, mist the patch and apply a second coat of plaster.
After the second coat dries, apply a third coat, this time using wallboard compound. Sand and finish.
If the laths are missing, you’ll need to create a backing for the loose plaster to adhere to. If the hole is small enough, crumpled newspaper or steel wool are good backings, says Morek.
Again, apply two or three coats of plaster, allowing each coat to dry thoroughly.
Medium-size holes. If the laths are in good condition, holes the size of a golf ball or larger can be filled in as explained above
If the laths are damaged or missing, however, you’ll again have to create a backing for the plaster to adhere to.
Damaged laths should be removed and any loose plaster chipped free. Score the edges of the hole with a utility knife.
Then, cut a piece of metal lath or wire mesh (available at home improvement stores) that is slightly larger than the hole. (See accompanying graphic.) Attach a piece of wire to the center of the mesh and fold it to insert it into the hole.
Then fold back the mesh and pull on the wire so that the mesh is flush against the inside of the opening. Attach a pencil, a paint paddle or a dowel around the wire and pull it tight so that it acts as a brace against the wall, keeping the mesh flush.
Mix the plaster to a thick consistency and apply it to the mesh. Apply a scratch coat, and after it hardens, snip the wire and remove the brace. Mist the scratch coat and apply a second and possibly third coat of plaster. Follow that with a coating of wallboard compound and sand and finish.
If the laths are damaged and the studs are exposed, you can also attach a piece of wallboard to the studs to serve as a backing for new plaster.
Apply the plaster to the wallboard patch as you would to the mesh in the steps described above.
Large holes: Large holes in a plaster wall are the trickiest to repair.
“My advice would be to clear the old plaster out and staple wire mesh over the existing laths to create a backing,” says Gozdan. “The consistency of the plaster mix is also very important. You want to keep it as stiff as possible.”
“With large holes, you’re going to be spending a lot of time trying to smooth out the plaster, which can be very frustrating work,” says Morek. “An alternative to that is to patch the hole with a piece of drywall.”
The problem is getting the piece of drywall flush with the existing plaster. That may require placing shims behind replacement drywall where it attaches to the studs.
“You would then tape the seams around the replacement drywall and feather the wallboard compound as best you can to match the drywall to the plaster,” says Morek.
If a large portion of the wall is damaged, you might want to consider covering the entire plaster wall with new wallboard, says Morek.
Wallboard repair
As mentioned above, wallboard usually is easier to repair than plaster because you can use solid replacement pieces. In using replacement pieces, it’s important that they be the same thickness as the existing walls’.
“Wallboard usually is 5/8-inch thick or 1/2-inch thick,” notes Morek.
Cracks: As with plaster walls, drywall cracks are fairly easy to patch. Remove any loose pieces and cover the crack with a drywall compound, feathering the edges to blend in with the existing wall.
Small holes: Holes less than the size of a golf ball are a little more complicated to repair. First, clean out the hole and remove any loose debris. Then, spread a thin layer of wallboard compound around the opening.
Place several pieces of wallboard tape over the hole in a criss-cross pattern, anchoring the tape in the compound. Then cover the tape with additional compound, feathering the edges of the patch.
The joint compound will probably shrink when it dries, so you’ll need to apply a second coat. Sand and seal after the second coat hardens.
Medium-size holes. These are a bit trickier to repair.
The first option is to enlarge the hole to a square or rectangle, creating an even opening. Then trace the opening on a piece of paper and cut a piece of drywall to match the hole.
Insert a small screw in the drywall patch to serve as a handle. Then, spread compound around the edges of the patch and insert the patch into the hole.
When the compound dries, remove the screw and add more compound around the patch. After the compound is thoroughly dry, sand and finish the spot.
Another method of repairing a medium-size hole is to attach a support bracket to the existing wallboard, similar to the brace used for the plaster hole. (See accompanying graphic.)
Again, recut the hole to a square or rectangular shape and cut a matching piece of drywall. Then cut a piece of 1 x 2 brace about four inches wider than the hole.
Apply adhesive to the ends of the 1 x 2 and insert it into the hole, pulling back on the brace so that it spans the hole and adheres to the inside of the wall. Drive two screws into the wall to catch the ends of the brace and hold it firmly in place.
Once that adhesive is dry, apply adhesive to the drywall patch and the brace. Insert the drywall into the hole and hold it in place until the adhesive dries. Then apply compound around the patch and over the screw heads. Once the compound dries, sand and finish.
Large holes. Large holes in wallboard can be repaired in a couple of ways. “The best bet is to locate the studs on both sides of the hole,” says Morek.
Cut a rectangular area around the hole, opening up the hole to the edges of the studs. (See accompanying graphic.) Cut two pieces of 1 x 2 that are slightly longer than the hole and attach them parallel to the side of the studs, so that the braces protrude into the hole.
Then cut a patch the size of the hole and, using drywall screws, attach it to the braces. Apply wallboard compound around the patch. Drywall tape around the seam of the patch will give it a more finished look.
If you can’t locate the studs, there’s a second patching method for large holes that’s similar to the brace method described above. Again, cut the hole into a square or rectangular shape. Using a piece of plywood, fabricate a brace slightly larger than the hole. Drill a hole in the center of the brace to create a fingergrip for handling.
Apply adhesive around the perimeter of the brace, insert it through the opening and pull back so that the adhesive comes into contact with the inside of the wall. Further secure the brace by drilling two screws through the wall and into the brace.
After the adhesive dries, apply additional glue to the drywall patch and the brace. Gently put the patch in place and apply wallboard compound around the seam of the patch, or tape the seams. Also, cover the screwheads with the compound. When the compound dries, sand and finish.
Ceiling repair
Holes and cracks in ceilings can basically be repaired as described above, but with one added twist: You’ll be fighting gravity. Hence, it’s important to keep both plaster mix and drywall compound at a very heavy thickness so it doesn’t sag.
“With plaster ceiling repair, the scratch coat is all the more important as you want to give the subsequent coats of plaster something rough to cling to,” says Gozdan. “Also, give yourself more time for ceiling repair in that it involves moving up and down ladders.”
