Another source yet for ballast!
When doing your ballasting you'll want to try and tie it in with the rest of the scenery for any given location as well as the material readly available there from a coloration, material and ground cover standpoint. Keeping some consistancy makes things a lot more believable and looks much more natural!
Now as far as looking natural your probably passing over and walking on something or it isn't too far away and its 'free' and that's dry dirt. If you happen to be anywhere near any cuts in hillsides of roads etc there is pleanty of loose dirt and rock in all different sizes which can be sifted too to get the desired consistency and various locations usually will yield different colorations to add interest to your layout for free too other than the time an a bit of gas. Just take a container or two along plus maybe a shovel or scoop. You might even have this available in your back yard as I do and in a variety of material consistencies.
So go outside and scout around, you'll be surprised at what is available as well as the variety to scoop up for free. Don't forget there are many types of small tree branches and twigs that can also be used for scenery too just lying around to be picked-up for free again.
As I've heard, in Paul Scoles Scenery Videos - really great information, use 3 parts of water to 2 parts of white glue and ad a few drops of dish soap to act as a wetting agent to get the misture to flow freely causing everything to readly adhere.
The fine non-clumping CL can be used but how much are you intending to ballast in that one shade? I'd say it would be better to vary the ballast along the main line and especially along spur sidings to different locations. Again dependent on the scenery and rock in that local.
It might make some difference if your talking mainline as compared to branch-line but I'm sure they would tend to make use of whatever is most readly available even on the real railroads.
HTH,
David