We are planning to lay a tile hearth in our fireplace but unfortunately, the concrete subfloor is quite uneven, see pictures. We have had this fire opening widened, so the black damp proof course is is where the old internal brick course was. There is only a small 1 inch x 5 inch area is the very corner where there is a void.
How can I create a flat even surface ready to lay tiles that is suitable for use under a wood burner?
I had considered using a Hardie Backer (concrete board) to cover this entire area, but this would add too much height. So if there is another solution I would like to try something different.
Would I be able to level this out with concrete?