I'm getting ready to put in a shower and was going to use poured concrete for the base. I'm told that there has to be some type of rubber matting material that runs partially up the walls to keep water from getting in between the pad and the walls. The pour will be on existing concrete floor, and the walls are block and masonry board which I planned to cover with tile.

Can someone shed a little light on this rubber matting material and it's application? I am not familiar with it at all.