Hello everyone,
the joints are filled elastically as describes and then only superficially sanded. I don't know the exact material, but you can press it in with your hand. However, the cut does not go all the way to the floor slab but ends a few rows of stones before.
The option with the cuts in the corners was denied to us because then "the maximum length becomes too large." So we were only given the choice whether to make the cut to the left or right of the door. Our expert also suggested that one could scrape out the joints between the stones in one area, but this was also rejected by the general contractor/mason.
: Currently, the 4 joints are located on the side walls of the house, which is probably the lesser evil. On the end walls there is much more masonry that would have to be cut (gable roof) and also the significantly better view, since these are the street/garden sides.
Best regards,
Simon