plaster and ceramic tile problem - please help

I started to lay tile in the bathroon around the tub area walls. I ended up breaking a tile when I screwed the water spout back on and just noticed it this morning. I decided to take the tile off becuase it was still somewhat wet/dry. I ended up taking off part of the plaster wall. Actually to be precise I took off about 1/8 inch of plaster skim coat that was sitting on top of the plaster. Now I have bare plaster and need to put the tile back on. But my problem is I don't know if the bare plaster should be treated with something to withstand moisture. I heard that plaster of Paris would do the trick. There no way I can re-do the whole way with new sheetboard. The whole bathroom wall around the tub is all tiled. I am wondering what to do. Can I just tile over the old plaster? The old plaster is hard, but if I scrape it, it will turn sandy and be brittle. I have about 1/2 - 3/4 inch of thickness for the wall and the old plaster is covered with an old wire mesh. I was also thinking that oil paint will seal it. Maybe I don't have to seal it.
Take a look for a better idea. http://pg.photos.yahoo.com/ph/uk69uk19/album?.dir=/a94f
Pic 2 of 4 is with the 1/8 skim coat of old plaster that I took off. Most of it was alrady off when I pulled the tile off.
I also need to back the pipe that is sticking out of the wall but it is in there really tight and I will mess the threads up if I grip it with a pipe wrench. Any ideas on how to get this out. I already sprayed it with wd-40. I need about another 1/4 inch from the wall so when I screw the spout back on it doesn't crack the tile again.
Any advice?
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A bigger problem may be that even if you could grip the pipe properly, insuring the other fittings in the wall don't break may be a larger issue. There are internal pipe wrenches made to grip the INSIDE of pipes. See http://www.acehardwareoutlet.com/productaddonsdetails.asp?id 29239&source=froogle
RJ

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Doobielicious wrote:

I can't help you with the plumbing issue but that's a relativley small area to re-tile. After you've fixed the pipe fitting situation you can clean any loose crap off of the plaster, brush on some Weldcrete, followed by a skim of thinset to make up your 1/8". Mix the thinset with acrylic latex additive instead of water. Bring it out to where it needs to be to allow the tile to go back on flush with the surrounding tiles. Let it set a day or so and then re-tile.
It's called, making the best of a bad situation.
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