all you need is very fire sawdust a strainer like this 
acrylic colour (I’ve used green Apple)
a pot
Put the sawdust into strainer for separete the big material from the fine what we need is the fine sawdust, after do that put colour in a pot and add somo water, now put sawdust and mix if necessary put other water or sawdust ultill the mix became enought dry
put the mix on plastics surface I’ve used a plate and wait for drying
the result is
this is an experiment fine flock on painted filter material
I will post the tree made with original product and mine stay tuned
Nice.
And how to make sand, for example for a desert scene?
Is simple chepest if you live near the sea you can take sand from it (important is the size of the grain it depend of what scale is your model)
I’ve a sample of Middle East desert sand it is very fine compared at the sand of my sea
another method is go at pets store (Acquarium store you can ask it for a punch of fine sand)
put the texture of sand of other materieal is alway a better way i think because give at diorama real details an important thing is painting method if you don’t have much time you can have nice thing with only two colours one dark and one light, with the dark make a backgound and with light you must do dry brush
for big surface use chepest colours you can use tempera paint or acrylics (a white and black you must have for make colour dark or light) (don’t use models painting too much expensive)
drybrush tutorial lilnk in Italian sorry
http://www.modelingtime.com/2009/10/highlight-drybrush-cockpit/
