How to concrete loose surface in hearth

Hi there all,

Hoping someone can help. I have just removed some cracked old tiles and adhesive from a hearth. I want to retile the expose area so that it is flush with the floorboards, so I dug out a little below the level of the old adhesive and have now exposed a loose base which appears to be some sort of compacted material, not a solid slab and comes up/crushes very easily.

Is it possible for me to simply pour concrete over this area and screed it off to about 2 centimetres below the level of the floor boards to allow for a layer of self-levelling compound, the tile adhesive, and then the tiles themselves?

Not sure whether I need to compact the loose material further, or place a layer of something over it (sharp sand?) before pouring the cement on? Also any advise on preventing the concrete dripping away beneath the floorboards at the edges of the area much appreciated!

Thank you,
Jon

The trouble with hearths is people stand on them and if the base isn't solid it might crack, so ideally you should scrape out the loose stuff so you can get a decent thickness, 3" if possible, then fill it with sharp sand and cement, not too wet, tamp it down well, put a thin piece of ply around the edge as a shutter if needed.

Hi there, many thanks for your reply. In fact, I had to get on with the job but I have pretty much done as above - probably scraped down 2-3 inches, thin layer of sharp sand then a 4:1 sharp sand:cement mix. Fortunately the front edge runs along a joist just below the floorboards but I shuttered out the sides with a couple of pieces of scrap hardboard. Seems Ok at the moment - I guess time will tell!