Questions & Answers

I may be overthinking this, but maybe not.

I setup a laser level and a story-pole, transferred ruler measurements to the pole, set the laser to zero on the pole, and chose a starting point (hallway). I marked zero, and marked the walls where the laser could reach into the room so I could relocate the laser and retain my index. Then I measured the variance in floor height at 16" square points throughout the room.

On one edge of the room, the slab is 3/16" higher than zero. At the other side, it can be as much as 5/16 lower. That's a 1/2" difference. It's irregular throughout.

The first image shows a flat plane intersecting with the plot points at the 3/16" high point. Most of where you see the lines is either at zero, or 1/16 - 3/16 above zero. Everything else is below zero.

Since my zero point index location is about 5 feet down the hallway, obviously I'm not going to fill up the entire room with self-leveling concrete and then end up needing to raise my entire slab by 3/16". It seems that I might want to grind down the area in the first image that's high and then go for maybe a 1/16" - 1/8" self leveling?

Or, are these tolerances too insignificant to need to worry about? I'm intending on installing 24x12 tile, which I haven't purchased yet because of this issue.

If I skipped dealing with the slab at all, I feel like I would end up with challenges as my first tile needs to be placed at the high point, which would mean it would slope down, and/or, if I wanted it level, I would end up needing to build up thinset anyway, which would yield a mismatch in floor height at the bathroom entrance and the hallway.