I won't get into how the cement board is installed, but it is important to keep clearance from the floor so that moisture can't "wick" up into the cbu.
Apply a generous bead of silicone along the bottom edge of the cement board, you may have to smear it into the area with your finger to get complete coverage. This also inhibits any possible wicking of moisture up into the board.
|Tape all the seams and corners with fiberglass mesh tape and use premium modified thinset to mud your seams.
At this point I usually tile the walls before putting a mortar bed on the floor, but in this case the customer hadn't purchased the tiles yet and I wanted to complete the mud work.
|Using a pre-mixed "sand-mix" and water ... make your mud similar to the consistency that you had for your pre-slope. A dry mixture that clumps together and molds into firm shapes.|
|Just shovel the mud onto the floor until you have enough to work with .... then the fun begins.
Using a straight piece of wood or a straight-edge of some sort, create a LEVEL curb along the outside perimeter of the floor. This curb is about 2" thick and once level will act as a screed to level and slope the rest of the mud-bed.
At this point the drain trap should be screwed into the installed section of drain allowing for a mud bed of about 1-1/4" thickness.
Protect the weep holes in the bottom section of the drain with a handful of small pebbles or spacers so that mortar doesn't cause blockage.