Here the fuel dump has been cated in a fine sand and primed with a blak primer. I made a lot of effort to get the sand to be about the same size grain as the texture already on the scenery. I used a very fine grain intended for decorative fake flower arrangements which I picked up at a dollar store.
And here is the finished piece with some GZG 15mm NAC for size comparison. It is painted using Delta Ceramcoat craft paints. Ceramcoat paints are actually a cell vinyl paint, and except for a few colors, has excellent pigment. I use it for almost all my painting. The shed itself was basecoated with Vellejo Gunmetal and then followed the directions here for doing rust.
I am pretty sure the "apstels" refered to in the article are by Bragdon Enterprises. I happen to have a set of them that I picked up at a plastic model show something like 10 years ago. Imagine my surprise to find not only was bragdon still in business...
They are still selling the 12 color set I have for the same price I bought it for a decade ago! (FF-R12 WEATHER SYSTEM brand Small Twelve color KIT). The dry adhesive in the powder worked like a champ and I was very happy with the result!
The directions with the powders said they did not require a topcoat, but as gaming scenery gets handled much more than scale models I went with a couple coats of Testors Dullcoat.