We are upgrading the bathroom and the floor (ceramic tile over installed over plywood) is out of level and the low spot is around the toilet. I had thought of using floor leveler but I now don't think that will work. It seems like floor leveler would just run down the opening for the toilet drain pipe. Open to any suggestions.

  • So you're implying that it's lower by more than the thickness of the flange which is pretty significant. I'm assuming this must be an older house so there is likely water damage that has caused the floor to sag there over time. Do you have access underneath to inspect for damage? Or are you simply mean the entire bathroom floor is flat but not level? In that case I'd be tempted to leave it unless it's obvious. How much do you think you'd need to build it up at the toilet?
    – topshot
    Sep 20, 2016 at 1:14
  • Yes, this is an old house. Unfortunately (at least for this) the previous owners finished the basement so these is a drywall ceiling under the floor joists. They also put .5" plywood and ceramic tile over the old floor boards. I have removed most of the tile and there is water damage around the tub which will need to be repaired. Also, the plywood does not extend under the tub. Front wall to back is a bit over 1.5" drop and about the same from side walls to center of the back wall. The toilet sits noticeably crooked. I'm thinking my best bet might be taking up the floor and sister joisting it.
    – Karl
    Sep 22, 2016 at 16:56
  • 1
    That's pretty sizable. Is the foundation solid at the dip? Sistering would be the best overall though obviously the most work as well since you'd need to take out the tub and sink cabinet, too. If you're up to it, go for it! Did pretty much the same in my house. However, it will be an added challenge unless you also take out the drywall below for reconnecting toilet (and maybe tub) drain. Could be done if you only put in the subfloor at those locations so you can still reach in the joist bays and then finish laying the floor once the drains are connected and tested.
    – topshot
    Sep 22, 2016 at 19:23

2 Answers 2


Depending on how large of an area is sunken, you could cut up the old plywood with a circular saw. Sister boards to the joists and add cross members to the cavities to raise the area to match the surrounding floor. Follow up with plywood and then cement board before tiling and you should have a solid, fairly level floor to work with. This can all be done easily even though the basement is already finished. This seems preferential to any floor leveler, since you'd actually be addressing the problem, which is a sunken floor.

It would also be a good time to inspect the existing floor joists and see how damaged they may be. If the damage isn't extensive, doubling them up my suffice, or you may need to replace larger sections entirely.


Self leveling products should normally be no thicker than 1/4 inch.

If it is less than 1/4" difference.

Simply cover the flange hole with anything from a plastic bowl or whatever generic item you come up with.

Rub some oil (cooking oil works) around the edge of the "bowl covering the hole" so when the self leveling product dries, you will have no problem removing the "bowl".

  • Thanks - good ideas, but I need much more than a .25" difference.
    – Karl
    Sep 22, 2016 at 16:57
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    @Karl You could use layers of 1/4" underlayment to reduce thickness of compound needed. I did that in a few sections of my house as well (up to 1.5" like your's). However, you need to verify the foundation and joists are good where the dip is first if you go that route. Plus I'm not sure how you'd set the toilet since the flange would then be 1.5" below floor level. IDK if anything exists to permanently extend the flange that far.
    – topshot
    Sep 22, 2016 at 19:29

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