To paint stonework, after the undercoat I do a dark grey in splotches covering mostof the surface. Then I do some green splotches. Then I do some sparse light grey splotches. I let that dry. Then, I water down some black gesso to about 50/50 and paint over the entire surface. I let it sit for about 30 seconds then dab away at it with a paper towel. This leaves the black in between the bricks, and evens out the rest of the paint.
Once dry it should be a lot darker. I then get the light grey and dry brush top to bottom with small, straight strokes.