Level the Bathroom Floor Before you Tile

by Peter Bales | 6th June 2011

There are lots of things to consider before you tile a floor, such as whether the framing is adequate and the floor is flat and how it will transition to adjacent floor coverings.  This particular bathroom needed some help before I even started thinking about tile layout or grout colors.  It was sloped enough that you could feel it and you could even see that the toilet was leaning slightly to one side.  (An odd feeling if you’re using it..  :) )  Whenever I come across this type of situation I like to figure out what’s going on from the ground up.  That means it’s time for a trip to the basement.

Fix the Framing

In the basement, I saw some obvious problems.  At least it should be obvious.  Just below the claw foot tub, the plumber had completely cut the floor joist to make room for the drain line.  Not good at all.  Other than this issue directly under the tub I couldn’t find anything to suggest that the room was sinking or that the framing was not right.  I do know that it used to be a back porch and that these are often sloped to help the water drain away.  Not sure why it happened in the first place, but the framing looked solid and, aside from repairing the cut joist, I’d say we can head back upstairs.

To fix the joist, I removed the blocking that was loosely tacked to the side (not supporting anything whatsoever!) and sistered an full length joist along side the old one that was cut.  With that done, I also added an extra support in this area by installing a treated 4×6 beam that spanned three joists with a 4×6 post supporting it atop a cement footer below.  This would make sure the weak area of the bathroom wasn’t going anywhere.

Back upstairs, I new that the floor was solid now, but it was still sloping.  I could have just tiled it, but I just had to do what I could to get it level.  It was time for a couple bags of self-leveling underlayment or SLU. 

To begin, I had to figure out how bad the slope was.  After removing all the fixtures, I got my four foot level out and started crawling around.  It turned out that most of the room was fine, but the last four feet of the room sloped about 3/4″.  It was a mostly even slope to the back wall. 

Self-Leveling Underlayment

Knowing this, I nailed some 3/4″ strips of plywood across the back wall as a guide and as a barrier to contain the SLU.  I made some marks on the floor to show the low spots that needed to be filled in and added some more filler strips of 1/4″ or 1/2″ cementboard so I wouldn’t need as much SLU (that stuff is expensive!).  Anyway, I psyched myself up and mixed some SLU.  You have to follow the directions fairly precisely and you get about 10 minutes to work with it.  After that it get’s too stiff to seek it’s own level and you’ll end up with humps and valleys if you mess with it. 

I dumped out the SLU and used some scrap wood to get it spread out a little but it basically does the work itself.  It does help to go along where it meets the subfloor and feather out the edge a little.  It dried in a few hours then  I installed 1/4″ Hardibacker over the entire floor giving me a flat and level floor to tile over.  Wahoo!

Tile and Finish

When you are raising the floor, either by tiling it or leveling it, or both in this case, you have to consider how the height change will affect the room.  For example, in this bathroom I spent some time thinking about how I would extend the drain on the claw foot tub with the higher floor.  I also had to relocate the shower curtain bars that that surrounded the tub to accommodate the higher floors.  These things are not usually a problem, but it helps to think it through as much as possible on the front end so you can make sure you make all the preparations along the way. 

Not only did this bathroom get a facelift, it got a floor lift.  It makes all the difference.

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