I just got a private message asking about the Grit Node and my rust metal presets, the effect wasn't showing up in the renders.
I do believe it has to do with object size and or grid scale in Layout. I have never gotten around to figuring it out for myself...I just load a scene with the effect I want (rust in this case) and then replace the old object with the new one and it works all the time. One of these days I'll take the time to learn, but for now...download this rust scene and have fun.
Oh yes, once you have GritNode plugin loaded, you can find the node in the following location in the node editor: Add node/Additional/ee_GritNode