I have a house that is 70 years old and I am in the process of re-plumbing the bathroom. I have ceramic tile over what appears to be a 1-2 inch thick layer of cement. I am using a masonry balde to cut the walls out. I want to add a shoer to the bath tub. Do I need to remove the 3 foot high ceramic tile wall aound the tub and redo the whole wall with wonderboard? Can I cut the plaster out above the ceramic tile, install wonderboard ensuring the wall is flush with the wall below and retile the entire height of the wall (assumming I take the ceramic tile off of the concrete wall)? Also, the exteriro wall is clay tile with a concrete mixture over it, can I chip off the tile and put new tile on and what should I do for prep? Sorry for the length. Thank You!