I’ve been using Rhino+Vray for some time now, but I’ve never seen this. Can anybody explain why there is what looks like fungus growing on the building? 
Materials that render fine on some parts of the model somehow turn black and patchy at other parts of the model. What is going on?!
Hi Adnan,
FWIW: might it be you have 2 overlapping/double objects in those areas?
-Willem
Hey Willem, no there aren’t overlapping objects where the discolouration is
happening. I’ve purged the file as well in the hopes of making it a little
lighter, but to no avail. The fungus persists!
Do you have any light sources that are touching or inside surface objects? --Mitch
Nope. Just the GI and a V-ray sun.
A couple of shots in the dark: In VisOptions, under color mapping, does Clamp output help this? What GI engines are you using? Does toggling the sRGB button on the V-Ray frame buffer (bottom left area of buttons on the frame buffer) have any effect? Can you share any part of this model that would illustrate the problem?
Sam