The wall is done, and now I started painting the concrete floor. Just finished that.
First I primed it, then it got a black coating. Next it was painted grey in several translucent layers of greys/khakis/tans. When all was done, I liberally added a splash of white spirit with a hint of browns and blacks in that. That nicely crept into all the tiny holes and cracks.
I already added a borderstone along the rim of the concrete floor, and added dirt and some grass to that. The grass is made from ... (??? what's the English name for this ???)

What's left now ?
- placing the wall on the dio base in such way it can't break off. (I"m still thinking how to technically do this. I think the solution will involve a steel

- fill in a 5 cm border with dirt and plants between the wall and the cornerstone. I'll use plaster for that.
It's the first time I make a 1/16 diorama, and it's FUN !!!
I'll try to make pics tomorrow, so you can follow up on this.