I'm not sure I understand your question ...Is the overlapped material underneath the plaster and lath or on the surface? If on the surface, and you don't think it's wall paper or NU-wall, then it may be canvas or some other attempt to either cover-up crumbling plaster or to provide a smooth surface for decorative painting. Why don't you want to remove it? (Other than it being a a nasty job to do.) Have you tried loosening it in a concealed area to assess how hard it would be to remove? You will always see those seams unless you sand them down, which might be a bigger pain than simpy removing the covering. A lot would depend on what your plaster is like underneath and whether you have rough or finish coat as a top surface. Perhaps your plaster is only rough coat and the paper was installed to make it easier to get a smooth finish. Another alternative would be to remove it and get a top coat put on. Or you could just slap a coat of paint over it and move on. As for cleaning, I wouldn't hesitate to use any cleaner, including TSP. Generally I prefer powdered products, rather liquids as I think the powders leave less residue. At the moment I am using up some green powdered laundry detergent, with out enzymes or optical brightening agents, and I like how it's going. (The stuff was a complete dud for laundry, though.) Some people wash with strong ammonia nd water solutions, but I hate that stuff. I have also used Lysol liquid detergents and been satisfied, but now prefer the powdered stuff. I have seen Spic and Span recommended, though I can't stand the smell. Another tactic is to use a steam cleaner. I have a Lady Bug, and while I'm not at all impressed with most of its uses, wall cleaning is something it does do well, though very slowly. (It can also steam wallpaper residue off, so try it first before doing a whole room if you choose to keep whatever is on your walls.) For primer, I have used Kilz and BIN, and both are very good but incredibly stinky to use (you really need to have an open window). Alisande's recommendation for using a good quality primer, is also good, particularly if you decide to just paint over the surface for now. With old houses knowing when to go whole hog and restore like crazy and when to just get things cleaned up and looking fine is the key to a happy life. Sounds like maybe just painting over your wall surfaces (after some cleaning) might be a good choice for you. Happy spring cleaning! Molly

I can think of no advantage of plaster over drywall except hardness of the finish and there are more important issues involved. The separation wall between the two units must have a fire-resistance rating and that is much easier to obtain with drywall. Here is the code requirement: "R302.3 Two-family dwellings. Dwelling units in two-family dwellings shall be separated from each other by wall and/or floor assemblies having not less than a 1-hour fire-resistance rating when tested in accordance with ASTM E 119 or UL 263. Fire-resistance-rated floor-ceiling and wall assemblies shall extend to and be tight against the exterior wall, and wall assemblies shall extend from the foundation to the underside of the roof sheathing." That means the wall assembly must have been tested by an agency like UL have have a published test number. These tests are expensive so there are few that are for metal lath and plaster. If the studs are wood, in bearing and don't contain plumbing, etc., the UL test number will be U 300 and U 399. The 1 hour rating can be achieved with a layer of 5/8 Type X drywall (U305). For metal lath and plaster, the the lath would need to be 3/8", 3.4 lb per sq. yd. diamond mesh expanded steel and the plaster would need to have a scratch coat of 2 c.f. of vermiculite aggregate to 100 ibs of fibered gypsum and 100 lb. of unfibered gypsum for the brown coat. (U315). The approved manufacturers of the materials used for each of the tested assemblies are listed for each test. there many more tests for drywall than for lath and plaster. It would be far cheaper and easier to construct and get approval for a drywall assembly with no loss of fire protection or sound separation. To improve the sound separation with drywall (I don't how to do it with plaster) add another layer and perhaps hang it on horizontal resilient channels. Seal the perimeter well and avoid back to back electrical outlets or other penetrations. It can help if one side is different from the other. There are many alternate ways to increase sound separation but the 4 principles are: 1. mass - the heavier and thicker the materials the better 2. resiliency - materials that move with the sound reduce it's energy 3. absorbency - materials that are porous slow and trap sound 4. no cracks - cracks and doors defeat the other principles To get the hardness of a plaster finish with the advantages of drywall you can use a veneer plaster system (blue board) if it is available in you market. It's just a thin coat of plaster on a special drywall board and far superior to taped drywall usually at no additional cost. This post was edited by Renovator8 on Thu, Feb 21, 13 at 9:39

Plaster on blueboard at least as practiced around here provides a much harder and smoother surface than drywall with absolutely no surface irregularities between sheets. It can take a lot more abuse without dents or scratches in my experience. Of course finding anyone around here who is willing to come back multiple times for a multi-coat drywall finish is really hard, they all try to tell you that a plaster skim coat is cheaper and faster. Given the speed that those guys work I can't imagine a multi-coat process being faster. Our whole house was skim-coated in less than two days and the plasterers were done and gone.

Thanks Casey, What is a good oil based primer. I will be using BM paints for the room. I could get their primer. I have only used Zinzer primers up to this point, in my kitchen, and now bathroom. My progress: Last night I went ahead and thinned down some green topped joint compound (drying type, I believe it is called, as opposed to setting type) and rolled it over the Gardz primed walls. After I knifed it off you could barely see the application, just a soft haze. My thought is that I will now apply another thin skim, then when dried, prime for painting. I just don't want these layers to delaminate in the bathroom. This isn't a steamy room because there is no shower and the tub is rarely used. But it is a bathroom none the less.