Need advice re: wall “filler” plaster
In the course of replacing a residential bathroom’s vent fan and installing a Solatube, I tore out the original plaster-on-board ceiling and replaced it with moisture-resistant gypsum board. I now need to tape the seams and edges. The original system had a band of expanded-metal lath around the top of the walls that extended out onto the ceiling for about 3 inches. To tear out the old ceiling, I cut the band where the walls met the ceiling plane. However, the old ceiling system was about 1″ thick and the new gypsum board is 1/2″ thick, so now I have a ragged gap of about 1/2″ to 1″ between the top edge of the original walls and the new ceiling plane. Tape and joint compound alone shouldn’t be used to fill or bridge this gap, but I’m thinking some other kind of plaster-like material could/should be used to fill and build up to where I can finish the job with regular fiberglass tape and joint compound. In most places, the gap is backed by the old wall’s board, but in a few places, it’s a true gap with nothing backing it up. Can anyone recommend a material or technique I should use to fill and build up the void? Thanks.
Foho
Replies
You could try setting-type compound (Durabond) for the first coat. (It doesn't shrink.)
Or, put up a molding.
Al Mollitor, Sharon MA
Thanks for the reference to the Durabond brand. Using it in the Search function yielded a wealth of information, including some for future projects.
Foho
I've been told never to use greenboard for ceilings, even in bathrooms. Perhaps because it gets flexible when it gets damp....?
Next time, (if there is one), run 3/4" firring strips before the rock goes on. Setting compound will work fine such as Durabond 90, then corner tape it like regular. Just make sure all seams between the plaster and sheetrock are taped. If you're fast with a trowel you could mix plaster of paris with joint compound on a 1 plaster to 2 jc ratio with some water thrown in to loosen it a bit. Let the plaster soak and absorb the water before you mix the two. This is what I always do. You get about 7 to 10 minutes work time, and it won't shrink.
Since it's only a bathroom, why not use a double layer of rock?? Would have been better to fur down and use regular 5/8"--your primer and finish paint (something with a sheen to it--not flat) are what keeps the moisture out. Greenboard has been known to sag and get soft--I'm sure regular drywall will do the same if you don't do a quality paint job. Another layer of rock is the best way to fill the gap--then your left with a minimal seam.
I heard a seminar recently on water issues by a guy who has 30 years under his belt as a building scientist. His statement was that paints have virtually no moisture barrier capability, in spite of whatever it may say on the can.
Vote # 2 for a second piece of 5/8 rock. Just as mositure "resistant" as green (read: you paid twice as much for a different color of the same thing) board. Me, jaded, naw. But the durabond - the real stuff, not the easy sand, great for filling voids. But try to get as few as possible. Voids that is. And keep the brown bag stuff below flush. Doesn't sand too good. Like, at all.
Long as we're talking DB. Builder I know, I'm still chewing on this trick of his. Don't know if I like it or not. He does curved doors. Archways. No door, just the opening. Anyway, forms the head up with masonite and skims it with durabond. I said YGBSM that ain't gonna hold up and he says he's been doing it for years. I've been in most of his houses, even a year down the road. No cracks . . . yet.
"If you pick up a starving dog and make him prosperous, he will not bite you. This is the principal difference between a dog and a man." - Mark Twain
Where the gaps are too large for easy filling with the Durabond already suggested, I reccommend Structolite or Gypsolite which are pearlited plasters. The pearlite (expanded mica ... they sort of pop it like popcorn) gives the plasters more body which makes it more viscous and putty like making it more useful for larger gap filling. Both of these products (but especially the Gypsolite) are slow setting and it is often useful to add some alum to the mixing water to speed the setting rate. You can mix them quite dry (in small batches) for filling the wider spaces. I also will bend a piece of metal lath and stuff it into holes or gaps that need more structure to hold and reinforce the filler. The metal lath is very spiky and rough on the cut edges and can usually be wedged into place effectively. In addition there are some plaster based floor leveling compounds that are very useful for filling holes because of their high speed setting. These I mix very dry to keep them stiff and in very small batches (because the working time is about two minutes) and they will set while you are troweling and can be wet carved if there is any overfill. These are also very useful for setting electrical boxes in block or brick walls. You can just hold the box in place while the compound sets. I like to use a silicone rubber margin trowel (made for tile grouting) to do this sort of patch/fill work.