I am remodeling my bathroom and discovered the floor sags through the middle of the room. I purchased a new tub and shower base for installation but I am concerned how to level these.

We removed the 3/4" wood flooring and plan to install 1/2" cement board and tile for the floor. The manufacturers recommend mortar underneath both the tub and shower base.

- Is it ok to place cement board under the tub and shower base and then mortar?
- To level these, should I apply the cement board, then shim the components to level, then apply mortar? What is correct?
- Does mortar serve as a method to level?

Any suggestions will be helpful. I alway try to do things right but this is a first for me