This is the method I use for laying and securing ballast. The track is in place and you’re ready for the next step.
Now is the time to make sure that all your track is in gauge and all gaps between track sections closed. If you don’t, you may have serious problems later on. These include derailments, uncouplings, shorted turnouts, blown power packs, etc, etc…
For ballasting, I use an 80/20 mix of fine and medium ballast. If you use fine only, the ballast starts to look smooth and boring after a while. The medium ballast adds some bigger pieces and makes the ballast look better. For securing the ballast, I use a 50/50 mix of white glue and water. Don’t use matte medium. You’ll destroy your track trying to take it up later. Ask me how I know. With the water/glue mixture, you can reclaim your track by soaking the ballast with water. The glue in the ballast will soften and you can pull the track up. When putting the ballast and glue mix down, be very careful not to get any in the turnouts. This could freeze the moving parts solid. I suggest moving the ballast into place with your finger, followed by a light brushing with a small paint brush, like a brush for painting models. This moves the ballast away from the sides of the rails so your locomotives and rolling stock don’t ride up on it and possibly derail. Be sure too, that the ballast doesn’t lay on top of the ties. This could cause problems with coupler pins. when you’ve finished smoothing the ballast, spray the entire track with a solution of water and a few drops of dishwashing liquid. This will insure that the water/glue mix goes through the ballast and glues it tight to the track. When you’ve done that, apply the water/glue mixture with an eyedropper or old glue bottle. Do the entire track, being very careful not to get it in the turnouts. Let this dry for at least 8 hours, better for 12. When the ballast is dry, clean the entire track with a bright boy or similiar eraser. A rubber school eraser works well, too. If you don’t do this