I know the way Don Bies demonstrated acrylic paint weathering to the r2 builders at C3 was to apply a good amount of paint ( mostly in browns, light and dark, very sparingly black) with a brush or rag. then dab and wipe the paint around with a cloth to get patterns and spread it. Then he would mist it and wipe the surface some more. Almost all the paint originally applied is wiped off, but the end result is awesome looking.
I know its R2 and not fett, but hopefully these couple pics of Don giving a demonstration will help illustrate what I'm saying.
Don Bies R2 weathering demo
Couple pics on this page and more on the next.