Muddy Tanks

I nice easy and cheap way is to mix Elmer's glue, some sand (I use the stuff from Rustall) and the Tamiya acrylic paint of your choice (Buff makes a nice dried mud look, something darker for fresh). Mix it up on a piece of cardboard and stipple it on with an olf stiff brush. Let it dry over night then spray with Acrylic flat.

Well, the most basic steps(s) in weathering an AFV is a wash and drybrush. When you drybrush, use lighter shades, and on the lower undercarriage use lighter earth tones. I also mix a very thin but dark brown wash using tube acrylics. Then I use an old paintbrush or toothbrush to flick on this wash onto the vehicle. If you have an airbrush, you can use Tamiya Buff, very thinned, and mist the paint over the model, focusing on the lower parts. This stuff is excellent in representing dust.
Also, if you want actual mud, you can try the following:
Take some regular earth from your backyard, or wherever. Dry completely and grind into as fine a powder as you can. Mix with water and white glue (about 60/40 ratio) and make a thin mud out of this. Splatter the mud over your tank, into the tracks, and all over the running gear. When dry, you can paint or leave as is.

I always find wet mud is hard to replicate and most often looks like your tank had a visit to the chocolate factory , dried mud looks a lot more convincing - one of my techniques is to grind up an brown earth-coloured artists pastel in thinners, until you get a 'sludge' paint it on, let it dry, and voila ;)

thanks ;)

Magila: What you can do is after you paint your model give him a wash with oils or use powders or the most easy drybrush and then put the mud.

I recommend you this page http://users.pandora.be/ronny.noben/website/intro.htm check the tips section, it will help you a lot, It help me always..

Gabriel Salazar