Reparing a hearth

[Griffo]

I live in a late victorian house. I am in the process of removing the old fireplace and inserting a firebasket. I have taken out the old fireplace. The hearth in the fireplace was built up using bricks and cement. I have removed all this and am left with a hearth at approximately flush with the floor. The hearth in front was made out of bricks and cement. I have removed this and underneath is the original hearth which is also approximately flush with the floor. This original hearth appears to be made out of a lime, sand, cement mix, is about 3-4 inches thick and rests on the joists(?). It is old and crumbling a bit around the edges.

My plan is to put a new layer of sand, lime, cement mix on both hearths, about 3-4 inches in depth. This would then give a single raised hearth. I would then put slate on top. Does that sound sensible? Or should I remove the old hearth and start from scratch?

[Palindr☻me]

I would be tempted to just make up a standard concrete mix and put that down and level it off. At that sort of size and 3-4" thick it should take everything bar a piano dropping on it. Lime and whatnot mixes are great for stone walls with a bit of movement but you need something stable so that the slates bedded into, or otherwise fixed to, the top don't crack.

If you do later put in a heavy woodburner, or equivalent, the concrete slab will take the weight.