The Fort Pitt High Railers do a lot of work on ballast and track side display. We use a lot of white glue and work the glue ballast, (mostly Brummy's rubber ballast), mixture with our fingers, to get a good glue to ballast application, complete through to the base of the track bed. The wet-water spray application is O.K. but seems to dilute the glue a bit too much, IMO. Otherwise as the modules get beat-around the ballast comes loose and has to be re-applied.
Some of the most recent ballast/module work.
Usually so much glue/water mixture is applied, garage floor clean-up is a major project.
If you look closely, you can see some of the ballast patch-jobs.
The green is a lot of different materials. Scenic Express, EX897B Green Adirondack Blend, is my choice for trackside green and applies easily along with the ballast and other detail.
Straight ballast before we add color detail.
After we tweek the ballast May be not just ballast, you should be adding other stuff.
Gargrave track/Ross Switches have been air brushed with Model Master acrylic paint, Railroad tie brown (4885). Top of rails are cleaned after application of paint.