For those using smaller sized ballast

Hi all,

This won't help in the actual computation of the amount of ballast you'll need,  but ...

Here's a tip for those using smaller sized ballast that will make your smaller-sized ballast go a lot further. Use larger-sized ballast to fill up to almost tie-height and to form up your basic ballast shoulder. Then do a second thin pass to "surface" your ballast layer with your smaller-sized ballast. This second layer of smaller ballast then only has to be thick enough to hide most of the bigger lumps underneath. See below

Forget that this is O-scale narrow-gauge. What we're looking at here is the concept of a 2-stage ballasting process that can be done relatively quickly. Here the base layer was done with HO ballast topped off with Woodland Scenics "cinders" as the second layer. The thin second layer can be added to between the tracks and ballast shoulder while the glue is still drying on the first layer. If the surface of the second layer doesn't appear "damp" a quick second pass with an eyedropper laying drops of glue only where needed will set the second layer.

The slowest  part of this process is the glue drying time. The initial pass with bigger ballast can be formed to shape pretty quickly using a brush to spread the ballast between tracks and along the ballast shoulder to tie-height. The second layer is dropped from a teaspoon being skated along the rails. Because this layer is thin. a teaspoon will get you probably several inches of cover before it needs reloading. 

Some of the "first layer" can be seen as ground cover between the tracks in the photo. For O-scale around a 1920's vintage coal mine, this size of rock would represent stone "waste", with too much stone in it to be sold as coal. And there was always a lot of it to be got rid of. So it was usually dumped where any fill was needed. The cinders represent "almost mud" in O scale. The "cinders" are also used for well-trodden paths and work areas. 

For your consideration,