Aquachic: This finish is a stucco product applied over the backer board. You do thinset scratch and brown coats, then two finish coats with the stucco using a pool trowel to achieve a smooth surface. I just completed a very similar shower and used a product called called "Super Shower Finish" made by Merlex Inc. It's basically a Portland cement combined with a polymer powder to make it waterproof.
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