ᐅ Single-family house from 1970 – slab foundation on strip footing / strip foundation

Hello everyone, I wanted to install underfloor heating and removed some of the old clinker tiles in the basement at ground level, which were installed wet back then. The resulting floor structure is rather modest – the slab does not have the best consistency, let’s say it’s lean concrete. Is it possible to remove 6-7 cm (2.4-2.8 inches) and then smooth it out with a cement-based self-leveling screed? Below the "slab" there is coarse gravel/topsoil about 15 cm (6 inches), followed by damp sand. The construction appears to be dry at first glance. I wouldn’t use tiles as floor covering – linoleum or vinyl instead – but would such a structure hold up? Completely excavating is too complicated/expensive. Regards

Oh, how fortunate that even Rumpelstiltskin doesn’t know what your photo is supposed to show :-(

---

https://www.instagram.com/11antgmxde/
https://www.linkedin.com/company/bauen-jetzt/

I can only assume that the cement screed has partially bonded with the so-called "pseudo" concrete slab. The entire structure is not very solid; back then (1970) they probably used more aggregate than cement, and the aggregate size is neither small nor consistent. I’m not sure what remains after chipping or hammering away. I’m concerned it won’t be a smooth and homogeneous layer, and I have no idea how one would level it. Here is a better photo from 2017 taken in the laundry room—there is no screed visible, and the texture of the slab can be seen more clearly.

If you want it done properly, everything has to be removed and a new floor structure installed.
It’s not that much effort. With a good hammer and 2-3 helpers plus 2-3 containers for debris, it can be done in one Saturday.
Then you build up properly with a vapor barrier, insulation, and so on.
Anything else is just sloppy work and will only cause problems.