My shower is original to the house (1950) and has a mud wall with 4" pink and black tiles over it. I want to re-tile the shower and update the fixtures. None of the tiles are loose or broken. By using a flat tool I am able to pop off the tiles without damaging the mud wall. The mud is surprisingly strong and in excellent condition. I would like to re-tile directly onto the existing mud... can I do that? Do I need to prep the wall at all if the surface is smooth and free of cracks or holes? The bathroom project would go from easy to very difficult if I need to remove the existing mud. Any help/advice is appreciated.

I just finished a total removal of a bathroom like you are describing.

HE** on earth,,

The walls are most likely wire meshed inside this cement/mortar mixture,the ability to remove the tiles may prove difficult as you do the entire room,I hope not,but be prepared.

IF! The walls are somewhat smooth(meaning less than 3/8th inch) and the cracks don't make tiles loose,(you can fill the cracks with a good polymer mortar),the skim coat you will have to apply for the new tiles will bring the walls out about 1/4 inch further than what you have now(@3/8" tile thickness and @1/8th" thin-set minus the thickness of the old tiles)

Areas to help you decide what to do and where.

The edges need to be as close to smooth as possible, I have used a belt sander to smooth the wall to ensure the area is even.

Around any fixture/ledge,etc... make sure these are almost 100% smooth,one tile sticking up and 3 laying down looks terrible.Things get caught,soap builds up,water back's up and causes all kinds of problems... etc.You get the point.

The skim coat can 'fix' some of the differences in the wall but not all.. I worked with a skilled(10+ years in the trade) installer and he was stumped sometimes,imagine what a novice installer would go through?

If your tub will allow for this extra depth,I saw go for it,but try some first.

Thanks KBC. I appreciate the info. The tiles don't come off easily... thin putty knife and a few well placed whacks with a hammer. The mud is thick and adhered firmly to wire mesh with what looks like an aluminum backing attached to the studs. Very solid construction. No flaking or looseness in the mud. No water seepage or mold whatsoever. I have a cast iron tub that is also in good condition and plan to tile up from that.