Help with my Cement Board

Having gutted an old 1930's bath, I've rebuilt it bigger and included a glass shower. I've done the tile floor and marble in the shower and on top of the soaking tub deck. Here is my question:  I used cement board under the entire box that holds the soaking tub, including the side that runs down to the floor. I like that cement board is waterproof. I want to put wood beadboard on top of the cement board to give the bathroom a nice vintage look - I tried Liquid Nails but it won't hold the beadboard to the cement board - any suggestions for a product that will work?

Thanks