The "mud" I used was a mix of Vallejo Dark Earth texture paste, brown ink and some "scrub mix" (static grass, clump foliage, foam flock and chopped lichen) that I'd prepared a while back. This was applies using a brush. After applying it around the tracks, sides and the lower hull, I then went a bit stupid and started lightly stippling mud further up the tank. I did that slightly too much and I'm not overly happy with the result, but the only way I can get rid of it is to strip the tanks back to bare resin/plastic.
I did finish painting and washing the batch of Aussie infantry last night. I took a couple of pics this morning before brushing on a coat of Klear.
I've also primed the 15mm tanks black today. My plan is to get the main colours down with the airbrush tomorrow. If I have time, I'll also try to paint the details, but that might be a job for Saturday.