Single-family house 1970 - Floor slab on strip foundation

Hello everyone, I wanted to install underfloor heating and have partially chipped away the old clinker tiles in the earth-connected basement, they were laid wet back then. The result is a modest floor structure - the floor slab does not have the best consistency, let’s say lean concrete. Can you remove 6-7 cm and then smooth it with cement self-leveling screed? Under the "floor slab" there is coarse gravel/topsoil about 15 cm, then comes wet sand. The construction seems dry at first. Of course, I wouldn’t take tiles as flooring - linoleum or vinyl, but would such a structure hold again? Completely excavating/digging out is too complex/expensive. Regards

Oh how good that even Rumpelstiltskin doesn't know what your photo is supposed to show :-(

I can only assume that the cement screed has fused with the "pseudo" concrete floor slab. The whole thing is not very solid; presumably, back then (1970) there were more stones than concrete, and the grain size of the stones is anything but small or uniform. I am not sure what remains after chipping/hacking away. I fear no smooth and homogeneous layer and have no idea how to level it. Here is a better photo from 2017 in the laundry room, where no screed is visible, and the "structure" of the floor slab can be seen more clearly.

If you want it to be proper, all of that has to go and a new floor structure has to be installed. It's not that much effort. With a proper hammer and 2-3 helpers and 2-3 containers of rubble, it's done in one Saturday. Then you build properly with a sealing layer, insulation, etc. Anything else is just shoddy work and only leads to problems.