I'm putting a bathroom in the basement. I need to have sub-floor in so I can install a tub and tile the floor. I was either going to use Dricore, or 5/8" OSB laid on top of DMX and fastened with tapcon screws. I read that Dricore isn't recommended for use under tile because of how much it moves, but what about the OSB/DMX?

  • Be sure to check the height of your toilet drain. They're often put in a bit sloppy and if it sits proud you need additional thickness to your floor or the toilet will sit on the ring and wobble.Often the alternative is to chip out the drain and re-set it which is a huge pain. Significantly shy tends to be workable, but if it's even a little proud it can be a huge pain.
    – K H
    May 5, 2021 at 1:58
  • Generally best practice for tile is to set the flange on top of the finished surface which is proud of the floor and not an issue. If it's much higher than yea maybe it will wobble. Best idea is to dryfit but I like the toilet drain lip to sit inside of the flange so the wax ring is mor of a backup rather than the primary means of diverting the sewage into the pipe
    – redlude97
    May 5, 2021 at 16:28
  • The toilet drain pipe is already installed and has a generous amount above the concrete. It will need to be cut. Will definitely compensate for the tile/underpayment.
    – EMAW2008
    May 6, 2021 at 3:00

1 Answer 1


I assume your floor is concrete in this case. I would use a decoupling membrane like schluter ditra or one of the competitors. You can thinset this directly to the concrete and then tile on top.

For the tub I would just use a mortar bed to support the tub and then attach the flange to the wall(s)

  • A mortar bed can be used to support fiberglass tubs and other non metallic shower pans. You would not use a mortar bed on a steel or cast iron tub. May 5, 2021 at 11:45
  • 1
    A cast iron tub does not need bedding. A steel tub (thin) does, in my experience - I've seen one flex enough to flake the porcelain off. I prefer plaster to mortar for bedding (does the job, but easier to remove if ever needed.) Be sure to put water (or sandbags) in the tub when bedding so it does not float.
    – Ecnerwal
    May 5, 2021 at 17:09
  • Ours will be acrylic.
    – EMAW2008
    May 6, 2021 at 2:57

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