I use thinned down (with 91% alcohol) acrylic paint for the basic wall wash and coloring. Once dried, I tried a couple of things for the mortar wash, firstly woodlands concrete watered down and secondly, when that attempt didn't work as expected, I tried the same thing with acrylic paint with the same results.
I think, I may have had two issues, one being the paint was thinned too much and secondly, I only used one "coat" of the wash and haven't built it up. The other problem I discovered was the paint wash not only settled in between the bricks, for the mortar, but also left a wash over the bricks themselves. Only way I could see of getting that off was to wet it down and gently dab and/or rub the color from the bricks. When I did that, I found I was also taking out the "mortar" between the bricks as well. So when I was done removing the wash from the bricks, I'd also removed it from between the bricks and was back at square 1.
That's when I tried the chalk and dullcote method.