Now that everything is in place, we need to keep it there. If you try to pour glue directly onto the ballast at this point, it will pool and bead, ruining all of your hard work. To prevent catastrophe, the ballast needs to be wet.
The trick here is not to use water to wet the ballast but 70% Isopropyl Alcohol. You probably have some in your medicine cabinet right now. It is cheap and easy to find at pharmacies and grocery stores. The alcohol will prevent the capillary actions of the water, allowing the glue to flow freely through the ballast.
Apply the alcohol with a spray bottle. Use a bottle that can produce a very fine mist.
Start by holding the bottle a good distance away and do not point the spray directly at the ballast. Apply a very light mist and allow it to slowly rain on the scenery. A direct spray or hard mist will disturb the ballast.
As the scenery gets more saturated, you can apply it a little more directly. Soak the scene completely. The glue will need to soak down through all of the stones or you will be left with a thin flaky crust. Great for pie - not so good for ballast shoulders.