I have an open fireplace where there used to be tiles in front as spark protection. We have now chosen to lay a marble slab instead, which is 30 mm thick. When we moved in, the tiles had already been removed for some reason, leaving only a thin concrete slab about 10 mm below the parquet floor. We removed it since the marble slab is thicker, and underneath it is sand. Under the sand, there is a concrete floor that is very uneven.
My question now is how and what I should lay on the floor before placing the marble slab. I initially considered leveling the floor, but I do not know how to achieve this since the concrete floor is quite uneven and there is nothing to attach battens to. It also doesn't seem like I can lay the marble slab directly on the sand, or can I?
Attached are two pictures showing how it looks. The slab is about 100cmx50cm.
