Wow. Really nice work this week guys. SIRT your weathering is just outstanding.
i finally got around to completing a rock wall face that I started before I expanded the layout. Like the walls near the coal mine this is done with ceiling tile. The tiles are broken to form an uneven edge and stacked.
I paint in Two processes, first is a spray paint using rustolium camo earth brown, this is to get in all the small cracks since the tile is light. Next I used earth color flat brown latex paint. When the latex paint is still wet I took some fine turf "grass" ground cover, poured some in my hand and "blew" it into the wet paint. This represents grass growing in the crumbling rock wall.
Here are some photos the first shows the contrast between the unpainted tiles and the first spray paint coat.