How-to-float-a-bathroom-wall, how to float a shower for tile installation. fat mud or wall mortar is used to create a strong, flat, level, plumb, and square substrate for tile in a shower.. Use a tape measure to mark the new wall, measuring from the existing wall. snap a chalk line along the marks (image 1). then measure from the ceiling to the floor joist above to determine the length of the studs (image 2)., hey iaskedforit, i like your name :smileyvery-happy: let's talk about getting your shower retiled. i worked for years in my store's flooring department as a specialist, so i've seen some interesting things customers have found under the walls after they pryed the tiles off.