I use cleaned beach sand from the beach in front of us. Once it is groomed and ready for fixing, I dribble the drug store mix of water and isopropyl alcohol until I know it has penetrated well into the depth of the ballast, but I don't keep adding it until I see it seeping out the bottom and sides of the ballast.
I do this for about 12-18" at a time because I don't want the ballast to begin to dry. I then take a bottle with one part yellow glue to six-to-eight parts water with some dish detergent added and I dribble that until the top 1/4-3/8" of the ballast is soaked....again, not waiting until the stuff oozes out the bottom.
What I use to apply both solutions is the original bottle with a mask under the cap of painter's masking tape, the green stuff. I prick it with a pin and also drill a small hole in the top. I get good control with this. To seal it later, especially the alcohol mix, I place a layer of plastic food wrap under the cap.
My 'less is more' approach is simply my way of ensuring that if I need to take up track, or adjust it, it only takes a few minutes of wetting it and letting it soften before I can pry up outer rails on curves if I get lots of derailments and shove cardstock shims under a few ties, then tap the ballast into place, add more as needed, dribble alcohol, and add a few more drops of the glue. Three or four hours later, the tracks are ready for use once more.
-Crandell