or add visquine on top of the plywood and then put on the backer board
no. unless the floor is very uneven
That is the proper way to do it. You need the thin set to act as a filler so there are no voids at all between the ply and the cement board. 1/4x1/4 notched trowel is the required trowel. This is according to tile installation ( both ATC and TCA tile guide line codes) and the cement board manufactures way to do it. Any questions you can e mail me through my avatar and check my qualifications there. GL
