I have VRay 3.0 for Sketchup. I know you can create and ExtraTex Render Element and apply an Ambient Occlusion map, but it will be projected on all surfaces within the model. Is there a method to apply an AO map to a specific material or should I just leave it out of my material maps?
You could use “Material ID” or “Object ID” to mask ExtraTex Render Element in Photoshop, currently “Material ID” pixel quality is better than the “Object ID”, so it would be useful if Chaos Group developers could enhance the Object ID render element in the future versions of V-ray SketchUp.
Yes, there is…its a procedural texture called VrayDirt and is integral to creating complex shaders. Chaos goups’s docs about dirt texture are here: Chaos Docs Basically put ‘dirt’ in the diffuse, then add texture to ‘occluded’ or just leave black for AO, and tweak parameters until it looks right. Main parameters are radius, distribution, falloff, and invert/doublesided. Have fun! 
Oh yeah, and add your main color or texture for the material to the ‘unoccluded’ slot. You can get more complex by nesting dirt textures within dirt textures.
I appreciate your help! I went through the process you outline, but wasn’t able to tell any difference in my material. Perhaps my AO mapping is too subtle or the lighting in my scene doesn’t bring it out. Just to clarify, I am supposed to put my texture in the unoccluded slot and my AO map in the occluded, correct?
Yes, that’s correct. A good workflow is to run VrayRT so you can see whats happening in real time, then change your occluded color to bright red while tweaking your VrayDirt parameters. The ‘Flip normals’ check box will also be very important to get your AO to show up - it switches from occluding convex to concave corners. If you are changing a your radius amount and nothing is happening, try checking flip normals and see if that helps. But having a bright color in your occluded slot while running RT is key…a lot easier to get a good result if you can see what you’re doing. Then once you get the coverage you want, pop your texture back in. I picked this up from the Corona render guy. I highly recommend watching his tutorials…they are jaw-dropping, in my opinion…they’ll really give you something to shoot for.
Thanks, that seems like a better approach! I appreciate you taking the time to explain this. Can you send me a link for Corona tutorials?
No problem! Here is a great one that focuses on using CoronaAO, the corona equivalent of VrayDirt.-----> https://www.youtube.com/watch?v=tF7wIRdxdwE He’s using the slate material editor in 3DS Max and Corona Render, so you’ll have to figure out how to nest textures in VFSU and translate some Conona to Vray stuff. But the workflow is universal and shows how you can ‘easily’ create realistic procedural textures…(at least he makes it look easy)… Also, here is a good one using VrayDirt in Vray for Max by Arrimus3D-----> https://www.youtube.com/watch?v=4-wSkPX4xqI Arrimus is a wizard in all things 3D and doesn’t disappoint here…he covers every VrayDirt parameter. There are a lot of other good tutorials on the CoronaRender youtube channel showing him constructing shaders and even whole scenes. Definitely all worth a watch even if you don’t use Corona. I learn something knew each time I watch and just translate it to use in Vray.
***I feel like I should note for anyone else reading this thread that, everyone using Vray for sketchup should watch all of Chaos Group’s own ‘quick start’ tutorials before trying to run vray. They did a stellar job on those tutorials and cover ALL of the basics and many advanced parts of vray for sketchup. So if you haven’t already, be sure to check out all of those, too: https://www.youtube.com/watch?v=qx8P\_0z\_juA&list=PLm2Irfq-UvZ0iC1UBzfH4YPkGM2R8R-p6
Cheers! 