Expanding Plasterboard Crack
I live in a building that was constructed in the 1960s. The windows are these heavy 6'x5' units made of aluminum with two sets of double pane windows on either side and with blinds sandwiched in the middle. They swivel open. Their weight causes all sorts of stresses and strains in the building. As a result of the building's architecture, the middle of one wall in a bedroom lies on the other side of where one of the windows open and shuts in my living room. Consequently, a crack has developed in the plasterboard. At first it was just a few inches long, beginning at the ceiling. Now it's spread all the way down to the floor. I could plaster over it, but I know from experience with other cracks in my apartment that it will simply re-crack along the same line, because these are essentially stress cracks and the stresses on these points aren't going away. So I'm wondering if there's some sort of flexible material that I could use to fill the crack that would still leave an attractive, flush finish and one over which I could paint. I was thinking of acrylic caulking, but that tends to shrink a little and sink into the crack. Any ideas? (The width of the crack is quite small — less than 1/16".)
Re: Expanding Plasterboard Crack
The cracks can be repaired, IF there is no longer any movement. Meaning, the crack width doesn't change in width, nor lengthen more on the ceiling.
However, for security, I would recommend more than a simple taping job over the crack. It would be wise to apply additional reinforcement.
When I am doing a long stress crack like yours for a client, I like to use BOTH drywall paper tape and fiberglass mesh tape.
Here's what I do. I apply the fiberglass first, in short 3 inch pieces, laying them down in a bed of mud side by side, close but not overlapping. Wipe out the excess mud. Then lay a thin layer of mud down the crack (lengthwise) and apply paper tape as one would do ordinarily. Carefully wipe down the tape to squeeze out excess mud. Top with a minimum of two coats.
You may find it easier to apply the paper tape course after the fiberglass application has dried.
What you have achieved is this: fiberglass for lateral strength, and paper tape for in or out strength. In most cases, this will do the trick, provided as I said, that the crack is no longer moving.
One more trick: you can paint on a plaster bonding agent over the area where your mud will go, before you tape. This will prevent the tapes from slipping sideway if additional stress shows up after the job is completed. This is not an essential step, but not a bad idea if you have the bonder on hand.
One last point. Use mud under the fiberglass. Don't relie on the stickiness of the fiberglass alone to secure it. You will significantly increase the usefulness of the fiberglass by glueing it down with mud.