The Razorbacks for Squads 2+3 have been attacked with my chalk pastels. Yup, regular artist's chalk pastels. They are cheap and last virtually for ever. I bought mine a few years (1990) back at my college bookstore. Basically, I rub a flat brush on the chalk to get some dust up and then apply it liberally to the desired dirty look. After the application looks good, the model is hit with a matte varnish to seal it. It can be done over and over, if desired... or you can add some paint weathering- drybrushed dust/dirt/mud/rust, paint chips, exhaust. But here's phase one on the razorbacks
And here is the dirty razorback compared to the unweathered camo Dreadnaught with the same original paint scheme so you can see the difference.
That's all for now, more stuff in the works. I hope to have both razorbacks and their 6 man teams done this weekend or shortly thereafter, depending on how many "distractions" come with the holiday weekend.