I am patching some plaster with some drywall and have shimmed out the drywall. The issue is that the plaster isn't a consistent thickness. Some spots it's flush and others its off by 1/8". What's the right course of action to level these out? Paper or fiberglass tape with that big of a difference would make the bulge worse. Heard of a product called fibafuse that might be good for this? Recommendations?
Drywall – Taping drywall of different thickness
drywallplaster
Related Solutions
If your house was built before the 1940's, it's probably a layer of wood lath, followed by a standard 2x4 stud wall with no insulation. Perhaps some knob-and-tube wiring just to make things interesting. The plaster will make more dust than you thought possible (wear a mask).
After the 1940's, it's probably gypsum board, but without the foaming agents and plasticizers that make today's drywall easier to use. Behind it, you probably have a 2x4 stud wall with no insulation and conduit or NM wiring.
[Here's a picture of a lath wall from the back, courtesy Wikipedia]
If wallpaper was painted over you could tell pretty easily by pulling on some of the peeling paint and breaking the paint chips. Wear a respirator mask while doing this, however, as often times flaking paint is a potential indicator of lead based paint. If the chips contain paper, then you're right, it's wallpaper with paint over it. If it's just paint, then be more careful - get the chips tested for lead.
Given the wide spread flaking, it is likely that the wall simply wasn't properly primed. An improperly treated wall when painted over will eventually lose adhesion with the paint and it'll flake away like you're seeing. If they applied paint directly to wall paper w/o priming, I think the same is true.
That 2nd picture DOES remind me of wallpaper... I've scrubbed far too much backing off the walls and that looks similar.
The grey subsurface is, I think, a kind of stucco mix that was often used to even up walls where lathe and plaster was replaced with the older style 2x4 drywall panels. It's nasty, gritty, dusty, unpleasant stuff, tougher than joint compound/plaster to work with because of it's tendency to crack and break rather catastrophically. When I run into that stuff in my rentals my approach is, "IF I have to touch it at all, it's ALL coming down." Plus with wallpaper I swear gutting is easier than stripping.
Now around the vent pipe, that looks like moisture damage. The bubbling around the pipe suggest water leakage. Is that a "finished" ceiling - ie - thats the roof on the other side of that wall w/ the pipe? If so, make sure it's properly sealed and replace at least that area of ceiling. Picture #5 seems to confirm this - someone touched it, and patched it badly.
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Best Answer
With uneven work like that you will have to build up the sheetrock side I use a wide mud knife at least 12" when trying to cover uneven areas, as far as the kind of tape paper or fiberglass I use both but preferr fiberglass in this case as it helps reduce cracking. Also I would not do in 1 coat but use several thinner layers. For areas like this I will use "hot mud" because it sets quickly and in some cases as soon as the first layer is complete the starting area is dry just don't mix two much up or you may have a mud tray that turns into a brick before you get done. The last caution is hot mud is tough to sand so I will put my base coats on then a thin layer of topping mud very easy to sand but it takes a day to dry.