You do undertand that cemete board of not water proof, much less even water resistant. It is stamped on the board moisture resistant. That should not be used in a bathroom in the shower area. You will be replacing it in a couple years. Water will soak thru the tile grout, and into the cement board. You will first notice tiles starting to buldge out and become loose. Use a fully waterproof product like Schleuter waterproofing products.
Handy Andy In Mt Airy NC