Leveling concrete for bathroom installation

Question

I am installing a bathroom in my basement. There is a low spot in the concrete right were the base of the toilet would sit. What is the best way to level this so I don't have a rocking toilet?

The area of the dip is right against the sewer pipe and is about 10 inches in diameter, and probably drops about 1/4 to 3/8 inches in depth. What is the best way to repair this?

I will be tiling the floor above, and I am just wondering if it would be better to use self leveling concrete or thin set, or some other product to take care of this.

Answer 1

I'd just use more thinset in this area for the tile floor. 10" isn't a huge area, 3/8" height isn't a huge height difference and assuming you start tiling somewhere else you'll need this extra thickness for the tile to sit level with the surrounding tiles.

You could use SLC first on that one area but it just adds another step for little value. If you were to add an extra step I'd probably just use thinset to pull this area up first. Most SLC needs a primer and you'd have to buy at minimum a bag so unless you have some other uses for the remainder easier to go with thinset.

Answer 2

Self-leveling products tend to be weak and chalky. I don't consider them a great substrate for tile.

I'd either use a vinyl cement patch as a leveler, or I'd just use the tile mortar. Either is fine. Whatever's convenient.

Answer 3

For really thin leveling you can screed thinset or use a product that doesn't doesn't require lath reinforcement.

Self leveler doesn't feather down as well so if you don't plan on doing the whole floor you can use a slightly different product from Ardex/Henry call liquid backer that feathers down to flat without a need for lathe. There are probably other products that are similar to this, it is just the one I'm familiar with