Should I use self-leveling concrete or mortar to level a patched area of concrete prior to tiling it?

Question

I had to repair cast iron pipe in the basement. This left me with a 2ft x 3ft hole in my tiled basement floor. We cut along the grout lines, so I just need to replace the tile and concrete.

Well, I have poured the concrete, but I was not able to get the concrete perfectly level.

On two corners across from each other, when I lay a tile down along those corners I notice the tile is not flat. It it is about a 3/16" inch gap.

I'm inclined to to get some Quikrete leveling sealant to bring everything up to level.

My buddy was mentioning that we could just use the mortar that we are using for the tile to fill the gap.

I'm concerned the tile will crack even with the mortar under it if we don't level it. But is 3/16" of an inch anything to worry about?

What do the tile experts here say?

Answer 1

If you just have 2ft x 3ft there's no problem using usual (not thin-set) mortar to level the surface - it will be cheap (likely cheaper that self-leveling concrete) and quite easy to do.

Thinsets indeed can crack if it's too thick and also they are not very strong - don't withstand compaction as well as ordinary mortar and so there indeed is a chance that you have tiles cracking after thinset applied too thick. How much thick is "too thick" is typically specified by the thinset manufacturer and I seriously doubt that 3/16" (which is less than 5 millimeters) would be a serious problem - that is likely within spec. The problem is you might have hard time applying the thinset so that the tiles perfectly match the uneven surface - it's much easier to do if the surface is even, although my tiling experience is quite limited and I guess there're ways to use the thinset on uneven surfaces and have good results.

Answer 2

Check the manufacturer's specs on the thinset you are using (or just call their tech support to verify).

Generally, if the variation in the floor is 1/4" or more then using your thinset mortar is usually not recommended for fixing it.

Even though you say it is 3/16", in my opinion, it would make life easier to just use an SLC