Shower Base and Tub Leveling...Confused

Discussion in 'Shower & bathtub Forum & Blog' started by swiederin, Oct 20, 2012.

  1. swiederin

    swiederin New Member

    Messages:
    8
    Location:
    Iowa
    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 :confused:
  2. johnfrwhipple

    johnfrwhipple I love these ACO Shower Drains - Best in Class

    Messages:
    3,939
    Location:
    North Vancouver, BC
    The sagging floor is your first "Red Flag".

    Before you go to far you need to understand how the floor was build (framed) and what is causing it to sag.

    Many plumbers, HVAC installers and the like wreck havoc on a homes construction. If I was quoting on your project and it had a large sag we would be investigating the entier bathroom subfloor and ripping it up to inspect.

    The floor joists could be overdrilled. Undersized. Wet.

    A main beam could be undersized. Wet. or settling.

    If your tub is free standing it may have 4 levelling legs. These would be set to the right height and then the tub lifted out. We like to use Mortar mix 2-3 bags and place some poly down over the sub floor in the center of the tub location. Then the poly back over the mortar mix and then the tub set back in place. Check for level. Then fill the tub with water.

    Then secure the tub to the wall studs (Gently).

    The poly under the tub makes sure the mortar does not stick to the tub so one day it can be replaced easier. The mortar does not support the tub or level the tub most times only adds mass in the center so the tub feels more solid and does not flex.

    JW
  3. cacher_chick

    cacher_chick Test, Don't Guess!

    Messages:
    3,244
    Location:
    Land of Cheese
    If there is a basement or crawlspace under the bath, I would be looking for damaged joists or missing supports and looking at jacking it to level and installing reinforcing members. If the structure looks good, you can pour in self-leveling compound and then cement board over it. You have to remember that any floor movement will result is cracked tiles and grout down the road, so fixing the underlaying structure is much more important than anything you do on top.

    The mortar for under the fixtures is set down in piles and the shower/tub base squished down into the piles. It is only there to prevent the base from flexing. Any shims that are needed under the "feet" of the base for leveling should be adhered to the floor where they are needed before setting the unit in the mortar.
    Last edited: Oct 21, 2012
  4. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,892
    Location:
    New England
    You don't need cement board (cbu) underneath the tub, but it doesn't hurt IF it is installed properly. All of the cbu manufacturers require it to be installed over thinset mortar and not just attached to the plain floor AND it requires plywood, and not planks, if you have those.

    Enough mortar underneath can (and should if the floor isn't level) get the tub level. IF done right, the tub feels much more substantial, and you're less likely to experience stress cracks.
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