Yet another version: The brick walls on this building are made from embossed cardboard. (Robin, do you listen?
)
Generally I avoid spray painting for weathering buildings. First I brush painted the walls with Humbrol enamel paint (#70, matt Brick Red) full strength. Then I added a very thin wash of diluted matt white, wiping it off with a soft rag. By varying the amount of the wash and the intensity of wiping I acieved the effect of washed out mortar running down the bricks.
Sorry for the bad quality of the scan.
Ron

Generally I avoid spray painting for weathering buildings. First I brush painted the walls with Humbrol enamel paint (#70, matt Brick Red) full strength. Then I added a very thin wash of diluted matt white, wiping it off with a soft rag. By varying the amount of the wash and the intensity of wiping I acieved the effect of washed out mortar running down the bricks.
Sorry for the bad quality of the scan.

Ron