More garden waterfall plans

I need to get out to the garage and start practicing with my brother's airbrush that he has out there, get used to how to handle the thing so I can use his airbrush to add details to the rocks when I build my wall for the waterfall and the grotto that the hot tub will go into. Since I am constructing the whole thing from cement, I think it would be good to do some airbrush touch-ups on the flat plain looking concrete before I add in stuff like lichen and ferns and other decorative elements. Give it more of a natural stone look than I would get from just the cement.