The best approach when installing cement board or other tile backer around a tub is to keep the cement board out of the lip area.
How to install ceramic wall tile around a bathtub.
If the tub is level start with a full tile at its rim.
Apply it to the wall with the bottom edge about 1 4 in.
Divide the dimension in half and make a mark there.
For a tub surround only install the backerboard and tile 12 inches above the tub.
Then apply a generous amount of thin set to the bottom bathtub tile and position it 1 8 in.
Follow the order shown in the diagram to snap the rest of the lines.
Above the lip of the tub.
I cover some of the specifics of how to layout and set up a tub to install tile around it.
Fill the gap between the tile and the tub with caulk.
To tile around a tub or shower start by measuring the height of the back wall from the lip of the tub to the top of the area to be tiled.
Diycrew hrvdiy renovision step by step tutorial how to install wall tile in any shower with any size bathroom tile including how to install tile in a nic.