Best bet is to remove the existing shower/tub -
You need to first create the shower slope – depending on the type of flooring you have underneath. If the bathroom is on the second story, that is another issue so to insure you do not get leakage into the roof of the lower floor. There are 3 ways to make the slope…First you can purchase a prefabricated shower pan (expensive), you can frame in a slope (a little more difficult in an already finished room) or the 3rd – which I would recommend in this case would be to make a presloping bed out of mortar. Proper slope in the floor allows all the moisture to drain, eliminating the cause of fungus, mold and odor. Most plumbing codes require a slope of 1/4 inch per foot, you can lay a bed of latex-modified mortar and trowel the slope onto the surface.
After the mortar bed has fully cured (or the slope is otherwise created), then install a liner over the sub-slope, you can use one of the rubber types (they look like pond liners and are made of pvc or cpe) you can also have someone hot mop the floor with tar. Make sure the liner extends up the wall a bit…around 9” and nail to studs…make sure you do not nail on the bottom as this will allow leaks. Then install a second mortar bed, reinforced with wire mesh and floated to the floor’s final slope. let the second mortar bed harden and cure for at least 24 hours. Make sure you get this smooth and level…you do not want bumps and voids that will cause your tile to flex (it will crack and fail if not flat). You may need to extend the drain to allow for this extra height.
Next step and before installing the shower floor tile, install the waterproof wallboard – (use black construction paper prior to nailing up the wallboard to prevent moisture getting to the wall studs and creating a place for dry rot, fungus or odors) positioning the bottom edge of the panels 1/4 inch above what will be the finished height of the tile floor to allow room for a control joint This allows the walls to flex without cracking the grout and loosening the tile. You can fill the void with backer rod and sealant. When installing the wall panels, don’t nail through the cement board and pierce the liner where it laps up the wall framing; place fasteners above the liner instead.
Now you are ready to thinset, tile….let cure and then grout.
I don’t have any pics of doing this…but I am sure there are YouTube’s or other such help online….I tried to be as summarized as I could so that the post is not overly large and gives you the steps in order…It still makes a pretty long post.
Good luck on your refurb….remember to take everything slow and easy…try to think at lease a few steps ahead. Sorry you did not get an earlier response. I typically hang out in LJ’s and only looked in here when Martin posted a request for folks in LJ’s to help out in here.