I have experimented with several of my "failed" models to create this rocky dirt effect on the wheels and they have all failed miserably. Heres an example of the effect im looking for

This model was done by Steve Zaloga and it has the exact effect im looking for, if anyone knows this technique, may you please share it with me, and make my frustration go away :-)
-NERVRECK-

Hello mate, i've done something similar, just take soem white glue, dilute it 50% with water, mix in some sand or small dirt (pick the size you wish) add to wheels and leave dry, after that paint in desired colour.

Ofc you will have to be patient and do one side at a time.

cheers

Mirko

So thats what it is glue, water,and dirt :-) Thanks Sensei I really like this effect ill give it a shot.
-NERVRECK-

You can mix water/glue/coffee grounds also.

You can use putty and dirt/coffee

For some grass mixed in you can add some static grass or trimmed down old paint brushes or snipped twine.

Coffee hmm I can also try that thanx slodder . Do I mix these mixtures with paint to get color or do I paint over them?
-NERVRECK-

i would paint over it because the texture of it offers some awesome drybrushing and washing opportunities. Also, how i did it was to dabble some white glue/water mix over where u want the dirt then drop some baking soda ontop of it....drys hard as a rock, but doing it a second time i would addd more variated courseness to the mix, coffee, baking soda, dirt from backyard, railroading ballast, sand, whatever you can find. Hope this helps
Ian

Some baking soda, white glue and water.. Add some paint to colour it.. grab an old brush and then stipple it on where you want it.. Poke the tips of the bristles where you want the build up and add as much as you need.. when its dry, repaint and weather as required...


Mojo

Here is anticipating your next level....diorama groundwork. Everything these guys have told you here, guess what...you do the same thing on a diorama only on a much bigger scale. What I have done is go around where I live and found different colors of dirt (a reddish color, yellowish, light brown, dark brown)gotten a large jar of it. The go to grocery store and buy a real fine (small holes) sifter. Sift the dirt and safe the super fine stuff. when you build your diorama base and have drawn your layout and put in buildings or built up areas. get some of that liquid white glue (Woodland Scenics is best) put in a spray bottle take your real dirt and spread it on your diorama the way you want it. when it gets to your liking then spray the white glue over it and let it sit for a day maybe hit it again with the glue. the trick is you have to soak it pretty good with the liquid glue. Woodland scenics and some other companies make different grasses you can use so check those out as well. You do those the same way as dirt. There is also "railroad ballast" (again with the Woodland Scenics) to use for rocks and gravel