I don't know what you all do but once spread, I spray ballast with water with a drop of dish soap in it. Then I flood the ballast with a 50 50 mix of white glue and water. When dry, I vacuum off any remaining loose stuff. The ballast looks natural but is rock hard with the glue. I know there is some iron oxide in my ballast but it goes nowhere when glued in place. No problems with my locos.