Flooring Tile - tile over plaster wall

I'm replacing a (too small) corner shower stall (34") with a wider (36" x 54"). The old wall tiles were glued with some unknown adhesive (mastic?) and when they were removed from the underlying plaster wall, some of the mastic remains and in places some of the finish coat of plaster chipped away.
The underlying plaster wall consists of sheetrock lathe, about 1" of mortar, then 1/4" finish plaster. The plaster wall is sound so I'm planning to apply thinset over it and tile away. My questions are:

1) how to best fill and smooth the plaster where the previous tiles were?

2) I'm assuming that thinset over sound plaster is okay, since it seems to be essentially the same material as backer board only thicker - and that the thinset will adhere properly even where the plaster wall has been painted - the paint is intact, in good condition. If I'm mistaken I'd like to know now.

Maybe this is in the archives - in which case I apologize for this post - but I can't figure out how to access archives for this topic.

thanks, Dan S.

Hi Dan,
I would use a good quality white thinset for this project something like TEC's superflex or the equivalent. Mix it thick to fill in the holes. (It will sag a little so you may have to do it twice in some of the bigger ones) Also I would test the painted areas by installing one tile and then try to pull it off after it dries. (so what if you have to patch another hole at least you will know one way or another.)
Regards,
Rich Gately (Tileman1)

http://www.gatelytilecompany.homestead.com