I'm working on my first AFV (M4 Sherman) and want to make it dirty. I've been reading the articles and posts on this site as well as Shep Paine's book on builing armor. I want it to look dusty but not muddy. I've applied some washes and drybrushing and will probably add pastels next. Does anyone have suggestions on how to attempt this look? I don't want to add putty to the bogies and paint it but I'm a bit lost on what to do with the hull between the bogies. Are drybrushing and pastels enough or do I need the putty treatment there to simulate dirt buildup?

Any advice would be greatly appreciated.
TIA...Kevin

Use a drybrushing technique with pastel chalks. Scrape or crush the pastel into a powder and use a flat brush.
Doesn't matter if you use too much, the excess can be removed with more brushing!

Pastels are OK, but to me drybrushing is a MUST! I use MM FS30277 Armor Sand and FS33531 Sand and I've gotten great results so far... Matters not weither it is WWII or modern, dirt is dirt IMHO...

Yes for built up dried dirt between the bogies....I use Celluclay mixed with eath couloured paints......then after I apply it.....I sprinkle some static grass over it and work it in a little bit with a brush.......so it looks like the tank has gone through a field in past rainy days and some of the dirt and grass is now dried on.......paint and dry brush this too and also put your pastels on it as it will tie it all together.

As odd as it seems, I have found dirt makes a great dirt. I usually remove some from the wife's flower bed, place it spread out in a shallow pan, and bake it at 350 f until fully dry. I then grind it up with mortar and pestle until very very fine. Then for dirt build up or mud effects I mix it with Artists Acrylic Gel Medium to what ever consistency and thickness you wish. It sticks to the model tenaciously and looks like dirt after painted with oils.

Another thing you can try is to use an airgun to spray fine mist on the lower parts of the vehicle to simulate dust. I like to use various similar colors, rather than just a plain mono-color, then use pastel to touch up and add a little variety. This can also be used for really dirty vehicles that have celluclay mucked about the suspension. One trick I used to good effect was to paint the lower part a darker reddish brown and then fade the color to a light tan up higher to simulate a muddy vehicle that is drying. don't forget the rust streaks with pastels.

Rob