...depends on what kind of scene you're attempting to duplicate, I use cork to replicate modern mainline high iron, where you see regularly maintained high shouldered ballast with not a weed in sight. For industrial areas where the track is surrounded by roads and accessways I just apply the track directly to the homasote or working surface and ballast it accordingly.
...to really give something a secondery or semi abandoned look, use code 70 track, remove some of the ties, and ballast it and apply 'weeds' so you can hardly see the track above the 'crud'...this looks quite effective if done right.
Lorne Miller