I am in the process of installing a Kohler shower reciever, walls and door in my half bath on the main floor of my house. It will only be used by guests, and I was planning on installing it on top of my 3/4" solid oak prefinished floor. However, the floor is not level and now I am trying to figure out how to put down a mortar mix in the corner, preferrably without removing the finished floor first. I have thought about simply laying a piece of 1/4 inch Backerboard down without anchors or adhesive and then making a thin set mortar bed on top, using flexible mortar. My concern is that the finished flooring will expand and contract over time, and twist up and down in the process. This will crack the mortar if directly on top and distort the Backerboard if it is secured directly to the oak. What else would should I consider, and are there any options that people have tried in this circumstance?
Thanks in advance,
Greg in Vermont