What is a good system for ballisting a new layout? Can one just use sand, wet it down. clean it up and spray with 50:50 glue and water?
sand tends to crack and produce debris if you don’t glue it down with a strong glue. I tried several products and found that commercial ballast is the best choice. or at least that’s my opinion 
I glue it down following the isopropyl alcohool / diluted matte medium or white glue method. pretty much like Joe Fugate’s tecnique, explained in the first issue of “How to build realistic layouts”.
Some good tips here-
Also, there’s a downloadable PDF that Joe Fugate did that’s excellent–I strongly reccommend it. The video is very well done.
Jim