How to Repair a Plaster Ceiling
Tom Silva helps solve cracked and drooping plaster ceiling problems
The plaster ceiling in our hallway is cracked and drooping. Nothing has fallen yet, but it could any day now. I’ve seen Tom Silva repair plaster walls with a glue. Can the same thing be done on ceilings?
—Trent Dohse, Omaha
Yes, it can. The process of reattaching loose plaster to wood lath with an adhesive such as is virtually the same for both walls and ceilings. And while this may seem like a lot of work, it’s easier, cleaner, and less expensive than replacing the plaster with drywall.
The first step is to stabilize the plaster so it doesn’t drop any further. Starting along the edge of the bulge and working toward the crack, use a 3⁄16-inch masonry bit to drill holes every 8 inches or so through the plaster directly beneath the wood lath. Stay at least 2 inches away from the crack.
Now put a 1 3⁄4-inch-diameter plastic washer—the kind used for attaching foam insulation panels—on a drywall screw and drive it through each hole and into the lath. Don’t pull the bulge back into position yet; just snug the washer gently up against the plaster to hold it in place.
Next, find the size of the gap between the plaster and the lath. The adhesive can bridge gaps up to ¼ inch. A wider gap usually indicates that debris is in the way, which has to be removed.
To measure this gap, make a feeler gauge by straightening a paper clip and bending it 90 degrees from one end. Where the bulge hangs down the most, drill a couple of holes through the plaster and stick the gauge’s bent end through the hole until it hits the lath. Mark the gauge where it meets the ceiling. Now, pull the gauge down until the leg catches on the back side of the plaster. Mark the gauge again. The distance between the two marks represents how far the plaster is separated from the lath.
For gaps of more than ¼ inch, you’ll have to go behind the plaster at the crack and clear out the debris. (If there is no crack, use a 5-in-1 tool to open up a 3⁄8-inch-wide slit down the center of the bulge, perpendicular to the lath direction, the length of the bulge.)
Open the crack or slit by gently pulling up the bulge on one side with the screws and washers. This will give you space to get in and remove debris from the bulge’s other side. A good tool for this job is a straightened-out wire coat hanger that has a 90-degree bend 1 inch from the end. Feed the hooked end between the plaster and the lath and carefully pull out the loose plaster bits. Check to see if any more debris needs to be removed by pushing the plaster up with your hand. If debris is still there, the plaster will rock at that point. Take care not to crack it.
When you have pulled out all the loose debris, ease the plaster back into place and slowly tighten the screws by hand to hold it there. Now lower the other side of the crack or slit by loosening the screws, then follow the same procedure to clear the debris from that side and pull up the plaster to within 1⁄8 inch of the lath. When you’re done, the bulge should be gone.
Remove some screws and washers and use the curved-tip syringe to spray Plaster Magic conditioner into the open holes. Move the remaining screws and washers to the conditioned holes and spray the unconditioned ones, as well as the edges of the cracks. The conditioner acts like a primer, ensuring that the adhesive bonds well with the lath and plaster. After 10 minutes, use a caulk gun to inject Plaster Magic adhesive into all the holes and tighten the screws slightly. Tightening too much can squeeze out the adhesive.
Clean the wall with a damp sponge, and let the adhesive cure for 24 hours. Remove all the screws and washers and fill the holes and cracks with thin layers of ready-mix joint compound until the ceiling is smooth and ready for paint.