drywallpatching-drywall
While patching my kitchen ceiling, I cut the hole larger to get to the joists and install my drywall "normally". On one of my edges the old drywall keeps crumbling away. My plan is to make the hole bigger still and toenail in some furring (a board to screw the patch to). However, every time I breathe near this edge it seems to crumble more. The original drywall is probably 30 years old. How do I keep this patch from growing?
The edge on the left is what keeps crumbling away.
A good drywall adhesive has much more shear strength than screws - and this is just when your glue is on the framing. So if you are doubling up the drywall gluing makes a ton of sense.
Just recently my drywall guys started using glue and I can say this, I hope I never have to demo these places because the drywall is ATTACHED.
All this being said the glue holds to the back paper of the drywall. What you are saying is that behind the drywall you don't have a solid base... then the glue won't work.
Also I am going to assume that crumbling drywall means moisture. While most glues will be fine with a little moisture, the back paper of your drywall will not.
Then we have to think about heavy tiles. Heavy tiles do not go on drywall. They go on a backer board.
You need to take out crumbling drywall, then install 1/2 inch Hardiboard, then install tiles. There is no reason in the world that you need exterior access to remove interior drywall.
Recap:
drywall can't be used for heavy tiles
Sounds like you tore off some of the paper on the face of the drywall. This is cosmetic damage and if it wasn't over a seam it doesn't need tape. Scrape the glue (go ahead and damage the wall a little), apply spackle, sand it, (repeat?), paint.
Anywhere with crumpled up paper sticking-out (will not sand flat) needs to be bashed in (using the corner on the butt of a small trowel) and filled; circles with a wet sponge never worked for me. Which is the trick for dealing with the fuzzies where the paper has delaminated and you're looking at a brown spot. Attempt to sponge these types of areas and then apply a skim coat of plaster or it will show in the finish paint. Use a damp sponge, DO NOT saturate the wall, or the entire section may bubble.
An 8-12" trowel makes doing large patches much easier, try not to leave too much at the edges where it meets the old work (this is the most important area to bevel sand). While sanding it, you should begin to feel a nice feather once the old paint starts showing through in spots.
This is kind you want, not a flat trowel with an in-line handle. Those require a bit more experience to use and you still need one of these. If you do buy both, a good tip is to bend the flat trowel a tiny bit, making it ever so slightly concave. This facilitates a nice build-up along the center and gives you an already good taper at the edges.
Best Answer
Sounds like a bad spot in the drywall, maybe caused by water damage, or physical abuse. You're probably best to keep cutting until you find a good section, though you may get away with simply taping and mudding the joint. The tape should hold the section together, so even if the plaster is crumbling it will be held in place. If you opt to just tape and mud, there is no guarantee you won't develop a crack in the future.
If it were me, I would keep cutting (at least to the next joist). If you're lucky the bad section will not extend that far, or at the very least won't extend farther than a full sheet of drywall. You could try to patch it with compound, but it's not likely you'll be happy with the results.