How to repair sagging plaster ceilings

Scott Gibson, Contributing Editor

What looks to be the original plaster ceiling in my house is sagging. I'm worried it will fall in, creating a heck of a mess if it doesn't actually hurt someone. Any suggestions?

Your question reminds me of one especially memorable evening in a house where we once lived.

My son Ben had a friend named Dave who was well over 6 feet and 200 pounds as a high school junior. Dave and Ben would often roughhouse in Ben's second floor bedroom, which was directly over the living room.

This went on for months, with no apparent harm to boys or house.

Then one evening we heard an enormous crash from the living room. A section of our plaster ceiling nearly the size of a sheet of plywood had collapsed, right down to the lath. Equally bad, big sections of the rest of the ceiling were barely hanging on. They hadn't collapsed yet, but their connections to the ceiling were pretty tenuous.

The old plaster just couldn't take all that pounding.

We used drywall to fill the big gaps and then we used a lot of plaster buttons (or, if you will, plaster washers) to anchor the rest of the loose plaster.

In hindsight, alas, our use or plaster buttons was completely inappropriate something I learned later on from Peter and Noelle Lord of Peter Lord Plaster & Paint (you can visit them on line at www.plasterlord.com).

Happily, the Lords didn't just criticize my work. They also taught me a better way to do these repairs.

Plaster buttons have limited usefulness

Plaster buttons are perforated washers with a screw hole in the center. The idea is that you drive a screw through the washer, through the plaster and into the lath to stabilize the plaster surface.

They work some of the time.

But the Lords would tell you the buttons only hold up an area about the size of the button itself, and they only work when there's no debris between the loose plaster and the lath.

Plaster buttons also can crack remaining plaster if they're screwed in too tightly. And they have to be skimmed over with plaster.

So what's the better solution? Glue.

Test, then repair

Instead of buttons, the Lords suggest using adhesive to re-anchor loose plaster.

To learn if your own sagging ceiling is a candidate for this sort of repair, start by checking to see how far the plaster layer has sagged. Push upward gently. If the plaster goes back into place with no more than one-half inch of play, and without any crunching sounds, you can fix your ceiling rather than replacing it.

Start by drilling a series of injection holes into the ceiling with a 1/4-in. carbide tipped bit. Here's the catch: drill the holes where you'll hit lath and not the space between two laths. And only drill through the plaster layer, not into the lath itself.

These injection holes should be bored every three or four inches. Then use your shop vacuum to clean out the dust and debris. The Lords suggest using a hand to support the plaster while you vacuum.

Next, squirt a little water into each hole with a spray bottle. This will dampen the old plaster and the old lath and help the glue dry more slowly, resulting in a better bond.

Now use a caulking gun to pump latex or acrylic glue into the hole until you just feel the plaster bulge very slightly. That's enough. Wipe away the excess with a damp sponge.

The Lords, by the way, recommend Liquid Nails floor or foam adhesive as a glue.

Brace the ceiling and let the glue cure

Now the ceiling needs to be pressed upward until the plaster is back against the lath, just where it belongs.

You can use plywood, 1/4 in. to 3/8 in. thick, and either screw it to the ceiling or prop it up with wooden supports from below. Don't forget to cover the plywood facing the ceiling with polyethylene plastic so it doesn't bond to the glue.

After 24 hours, take away the supports. Let the glue cure for another day, then scrape off the excess glue.

Fill the holes with Durabond or joint compound and you'll have a fully restored, tightly bonded plaster ceiling.

But, just in case you'd rather do this sort of repair only once, don't forget to send the boys out in the back yard to play.

About the Author
An accomplished woodworker and carpenter, Scott Gibson is the former editor of Fine Woodworking magazine, and a former editor at Today's Homeowner and Fine Homebuilding magazines. He also is former managing editor of the Kennebec Journal, a daily newspaper in Maine.

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