I have one of the Necromunda Zone Mortalis: Floor Tile Set on my workbench.
I have given them a base coat of Mechanicus Standard Grey Spray. They then got packed away for a while.
Thinking about next stages, initially I was going to give them a wash or a shade. However due to the size of the boards, I was a little reluctant to use a Citadel Shade, I think I would need a few pots to cover the tiles effectively. I may look to see if there is something else I could use.
However, looking at the photograph of the finished tiles on the Games Workshop website, I think in the first instance I could do some heavy weathering of the tiles before giving them a shade. Adding some rust and dirt.
After shading them, I would then dry brush and then do some further weathering.
Now to find them….