Hy,
Some time ago ,i was made a diorama with snow...you can see it in my blog.

http://uss-prizuttu.blogspot.fr/2011/05/salut-tous-voici-comment-realiser-de-la.html

Hello. I tried using baking soda on my Opel Blitz build. I decanted some hairspray and applied it to the groundwork by brush. I put some baking soda in a small plastic cup and applied the baking soda through a small strainer to catch any large clumps. The more baking soda you apply the better it looks. I found that by applying a small amount of baking soda to the hairspray gives it a slushy look like on the side of a road bed. You can see my efforts on the 3/4 Ton Cargo Truck build over on the Axis forum. Hope this helps, your getting some good info with your question from other builders about this technique. Wingman out.