Black 2cm thick tar layer instead of screed??

By the way, it was asphalt screed. A recording from 1955 under the wallpaper provided the answer :)

Well, then it must be true if it was written under the wallpaper!!
Only: bituminous screeds were rare in the post-war years - also considering the prices at that time - and furthermore, the terminology from the 1955 era should not confuse us today or lead us astray, since (also) the nomenclature and thus terminology in construction have changed since then.