I'm in the planning stages of modeling a small building that was covered in spray polyurethane, used as insulation. It adds thickness to everything and things like windows and doors are "sunk-in". It has some texture but not as much as stucco. Being somewhat smooth in texture but somewhat bumpy overall. Think of a frosted cake; you might have smoothed it but the frosting could be thicker in one part and thinner in another.

Here are two photos.  The first is a photo of the White River Junction coal tower -- in the 50's at an age of 30 or so. The second is my attempt at weathering my model of that tower.  The challenge here is two fold-  one is to get the right overall color -- which is a grimy brownish grey.  The second challenge is creating the illusion of the lines in the concrete which were left when the concrete forms were  removed.  I tried all sorts of things to create a sense of the concrete form lines - without much success (light pencil lines, brush strokes)

In 2016, I rode behind 4501 from TVRM across northern Georgia on one of their day long excursions. I saw this shack as I passed by and got interested. Turns out, it shows up in a lot of photos and video of those trips:

http://www.railpictures.net/photo/652506/