Does anyone know what did they use to do on the floors years ago. It's the black stuff on top of concrete. It's about 1,5'' thick. Is it tar? It's very hard but hit with hammer brakes like rock or coal. It's also painted(impregnated) with yellow 'paint' - very slippery, almost like glass. On top of that there must have been some sort of (vinyl/wood) tiles as there's dark-yellowish 'laquery' adhesive that just peels off. Customer bought the house with laminate flooring covering it. I removed that adhesive(dark-yellowish) and treated the substrate with sbr/cement slurry (over that yellow 'paint' which is stuck to this black substrate). It seems working. Is there anything I should be warry of? Like asbestos or anything like that or lack of strenght on that substrate to receive tiles? I only did small part so far

it sounds like an old bitumen floor ,

Slurry coat as you have done is the route here..

I just spoke with the other tradesmen working late and we came to a conclusion that it's asphalt but properly cured over the years. It was different to the one freshly laid in the extension(another issue raised in my thread few weeks ago) but now the one in the extension is as hard as rock as well( I broke piece on the edge) and looks exactly the same.
The light yellow stuff is probably some kind of sealant, probably not to let oils to get to wooden parkett and to give base for wooden parkett adhesive(?)(-the dark-yellowish layer which peels off like old varnish under mechanical pressure).
You can see the parkett marks(layout lines: /\/\/\/\/\/ ) on that adhesive. There was also room next to it(now wall removed) with old asphalt but no yellow sealant and no parkett marks or dark-yellowish glue. So on that note yellow stuff must have served as preparation prior to laying parkett.
I only hope none of this contains asbestos.
Thanks for all the interest on the subject and hope it will help someone in the future.