What is under the flooring?

Hello, I started removing the floor covering in our living room today, it is not exactly easy because the floor is very old and was glued. Under the covering there is a black layer, similar to tar. Is it tar or what is it?

Maybe someone can help me.
Thank you

That will be the screed, probably mastic asphalt. We had that inside as well.

Caution! This could be a tar-containing parquet adhesive or a cast asphalt screed. Both substances contain PAHs (polycyclic aromatic hydrocarbons), which are considered highly carcinogenic. Since they are firmly bound, they initially do not pose a danger. PAH compounds usually enter the body through food and in individual cases are also absorbed through the skin due to their fat solubility. There are no limit values for PAH exposure. Until the 1960s, it was common to use PAHs in tar adhesives for bonding parquet floors. Afterwards, they were replaced by newly developed synthetic resin adhesives. However, tar adhesive was still used for laying wooden block paving until the 1990s. To be completely sure, you can take a sample and have it analyzed. The PAH adhesive must not be removed as a DIY project under any circumstances. Protective measures must be observed and a targeted procedure for removal, based on TRGS 524 (Technical Rules for Hazardous Substances / Protective Measures for Activities in Contaminated Areas), must be followed. The qualification for removal including the necessary protective measures must be demonstrated in advance by the executing company. Disposal must also be documented. If possible, the adhesive should preferably remain untouched on the floor. Mechanical treatment (sanding, etc.) is strictly prohibited due to the carcinogenic dust generation.

When removing the floor covering, some of the black layer remains on the concrete floor, and other parts stick to the floor covering. Theoretically, can a new floor be laid over it without exposing oneself to health risks?

Why are you removing the floor covering? If it adheres well to the screed and is level, a new covering could be laid/glued over it. If there are issues with the build-up height, it may of course need to be completely removed. The floor covering including adhesive residues is considered hazardous waste and must be declared and disposed of accordingly. The PAK adhesive residues on the floor remain and must be leveled off with suitable filler material or self-leveling compounds before the new floor covering is applied. All components must be coordinated with each other. Expert advice is also worthwhile before starting the renovations. So: first research + check, then think/ask/get advice, then build. In this order. That is more cost-effective.

The floor adheres well to the screed but must be removed because otherwise there are too large height differences. You wrote above that these must be removed by a company. Now you mentioned that they can be leveled with suitable filler material. When does a health hazard exist for me?