I'm putting a fireplace insert into my masonary fireplace.
The hearth extension must now be 19.5" (it is 16" at the moment). I've remove the existing tile along with the concrete bed. The fireplace is built over a counterlevered slab poured at the same time as the original foundation. I've cut a portion of the hardwood to the required dimension but now I need to make everything level for the new tiles.
What product should I use? The thickness needs to be between 1" to 3/8" and it needs to be non combustible.
Either product you mentioned and several you didn't mention will work. The trowelable products may produce a challenge that the Self Levelling Compound would not but the SLC would likely have to be temporarily formed.