The much anticipated visit of our infant grand-niece recently inspired us to clear out a spare bedroom in our old farmhouse and turn it into a nursery. Top priority was replacing the stained 1950’s era wallpaper with a fresh coat of paint.
Having done this several years ago in the living room and hall I knew what we’d find as we started to remove several layers of old wallpaper.
I wasn’t surprised to find:
- cracks of various sizes
- fist-size holes of crumbled plaster
- loose plaster due to broken keys
All easy to fix once you know what to do.
Step 1. Evaluate the wall condition
Look for signs of moisture or recent movement to determine if there are any structural issues that need to be addressed before repairing the plaster.
Since we were reasonably sure that the house is stable and there are no current water penetration or settling issues to deal with, I got down to the task at hand.
Step 2. – Stabilize the Old Plaster
First thing to do is check to find where the plaster keys may have broken and the plaster has detached from the lath. Just push gently against the plaster especially near larger cracks, and look for sagging plaster on sloped walls and ceilings. If the plaster feels like its loose (as opposed to a slight "flexing") then feel around some more until you find where the plaster feels secure to determine the extent of the repair area. DON’T REMOVE IT!
The good news is you can re-attach plaster to the lath with plaster washers. These look a bit like an umbrella with holes in it and work with a conventional 1 5/8" drywall screw or stainless steel screws. You probably won’t find them in your local hardware store but fortunately you can get plaster washers at Amazon.
Installing the Plaster Washers
- Start near the secure plaster and work your way towards the crack or a corner, driving a screw with a washer on it into the lath every few inches or so. The screw should pull the washer into the plaster just enough so that the screw head is below the surface and the washer is slightly concave.
- If the screw just spins without seating you’re between the lath strips. Take it out and move it up or down about a half-inch and try again.
- Work your way along the crack so that you’re not creating any bulges – like smoothing out a piece of fabric. You’ll quickly get a feel for how to do it and where to place them.
- Run a 6" drywall knife over the washers to make sure they are below the surface.
- Use enough washers to stabilize the plaster & don’t worry about creating small cracks and depressions around the washers since these will be filled with compound.
HOLES & CRUMBLING PLASTER
You’ll probably have some areas where the plaster has crumbled between cracks or places where furniture may have banged into it. The only option is to remove the crumbled plaster – if it hasn’t already removed itself.
Scrape away the crumbled plaster until you reach an edge that is still solid and attached to the lath. Again, plaster washers can be useful to button down a edge if needed. Fill any holes with 3/8" drywall or scraps of wood that are thinner than the plaster. This will give the setting compound something to grab onto and fills up the bulk of the void.
CRACKS IN THE PLASTER
Now that you’ve taken care of the loose plaster it’s time to deal with the cracks.
Don’t worry too much about the tiny surface cracks but anything that you can tell paint won’t cover needs to be filled. Just smoothing it over with spackle won’t stand up because you can’t get enough material in to bridge the gap.
Use an old punch-type can opener or similar pointed tool to gouge a v-shaped groove along the length of the crack. Don’t go all the way to the lath but make sure you create enough of a groove for the compound to settle in and add strength to the joint. Reduce the depth of the groove as you near the end of the crack.
Step 3. – Crackfilling Plaster Walls
Use a setting-type compound like Durabond 90 for the first application to fill in the larger holes and cracks. This fast-drying material comes in powder form and must be mixed as you need it. It’s very strong and hard to sand so aim to keep it at or below the surface of the surrounding plaster. The Durabond will add strength to the repaired plaster and provide a stable foundation for finishing the walls using conventional drywall techniques and materials.
- use drywall tape for large cracks & corners
- use premixed joint compound
- add at least two finish coats (use 6" & 10" drywall knives)
- scrape off ridges between coats with drywall knife
- feather edges to the plaster with 220 grit sandpaper
Plaster walls usually have some variation in thickness and are sometimes a bit rough in spots which adds to their character. Your goal should be to end up with a wall that’s solid and reasonably smooth but it might not necessarily be "flat".