After you apply your dirt and gravel spray the area with a fine mist of water to wet the surface. Be generous to allow the water to soak into the dirt and mix with the thick surface of glue. This will then wick upward to the layer of dirt you have applied. When this happens you will see layers of glue appearing, then sprinkle finely screened dirt onto these wet glue areas.
When you pour on the extra heavy layer of dirt and rocks, they must be glued using an extra pouring of water and white glue. I use a small squeeze bottle for the glue mix. The glue is applied so that it soaks the dirt and rock mixture thoroughly.