This is wonderful, if you don't have this node then you need to get it now...Download Grit Node Here!!
I've been trying to create a rust via nodes in Lightwave ever since I finished my ray gun model and now it's too easy.
Here is a quick five minute test using the standard scene from preset central. I think I should have used the 10cm scene instead of the 1m one, but you get to see a little hint of rust :)
I modified the scene object so there's more areas for the rust to show up.
The same node as it looks on my ray gun model with out modifications....the potential is great.
Here is the Rust Preset, download it and have fun.