How To Simulate Caked Mud and Dirt on Zombie Clothes?

I am putting together a "Nate" costume from Creepshow, and I'd like to find some techniques to add mud and caked dirt effects to the distressed clothing, without using the real thing. I don't want to leave a mess wherever I sit when wearing the costume. Does anyone have any ideas on how to build up this kind of effect on fabric?

Ideas I've considered: caulk or foam insulation for bigger globs, moss / glue , paint, fuller's earth. Right now I have a pristine suit I picked up from the thrift store.

Here are some reference photos:

 

Hmm. Maybe you could sponge layers of latex onto the suit with color mixed in to the latex?

 

what your looking at is a sculpted prosthetic and then layed with fake leaves

 

I did a mud/dirt simulation years ago for a WW1 vampire/soldier costume and needed the trench coat and gaiters to look heavily caked in mud. I used elmers (PVA) glue with latex paint mixed in, then added sand. I then caked it on real thick in various layers on the material. For spots that I wanted to look like wet mud, I used clear elmers with liquid RIT dye and sand. It dried with a gloss finish and looked wet. Check out the following link for images.

http://www.therpf.com/showthread.php?t=140634&highlight=baltimore+vampire