The hobby can get expensive sometimes, so if there are ways to save on a little expense, then I'm willing to do a little experimentation. We have a small pet lizard at home, and it suddenly struck me that the substrate used in his vivarium, is pretty close in size and shape as the bags of Woodland scenics medium and fine ballast. Although the colour is a bit light in our case (it is supposed to simulate a desert landscape) it can be toned down with weathering powders etc. It is made from calcium, so do be sure that you don't get any loose pieces anywhere near the track, as I'm not too sure what it would do to the gears in your precious locomotives, but I'd say this product is great for a variety of uses. The product is called 'all natural Reptilite calcium substrate', and is available from the better pet shops. It comes in 20lbs bags (a little over 9Kg's) which should be enough for the ballast needs of many layouts, and covers quite a large area of ground if you use it as your base ground cover. It comes in a few different colours, but they are mostly all pretty close to desert shades. It's worth considering this material as an alternative. If you plan to use this, and this being a natural product, I suggest to put some on a few baking trays and cook it in the oven for 30-45mins at 200 deg C or more. This will kill most bacteria and beasties that may be present, although it is pretty clean out of the bag. Do the same if you use mud etc from your back garden or from other sources. (to keep the peace with your wife/partner, use old trays or buy a few cheap ones for your exclusive use :-) ). The picture shows some of it cooling off, after receiving above process, and gives an impression of it's colour.