The grout is not anthracite but partially gray?

I can tell you that later. The craftsman is coming today. I am not doing it myself, but having it done as part of the [Mängelbeseitigung]. The stuff comes directly from the [Fugenmörtel-Hersteller]. I can report the result this evening.

So, the stuff comes directly from the grout manufacturer. For me, it's Sopro. The stuff is called Fugenfrisch. You obviously have to use the color of your grout. It looks great, everything is uniform now.

That sounds great already. How did he manage it and clean the tiles afterwards? What steps need to be followed?

I ordered anthracite as a test run

Simply apply to the joints, then wash off with water and a sponge after a short exposure time. Afterwards, it is walkable but should not be cleaned with detergent for 3-5 days. It looked totally easy and simple.