A brief update as I keep playing around with oils for weathering. I have used oils extensively for weathering on vehicles but its been a different experience trying them out on building. I decided to start with "old" weathering first. I'm trying to build everything up in layers and start with deeper grime first then work in the rust stains and then follow up with a lighter layer of "dusty" weathering at the end.
Its definitely been different working with these oils just on the sidewalks. I started back in to quickly and pulled off a lot of the light/dark shading work with the next layer of oils, it just had not dried enough for this treatment. Hiding brush marks has been quite the challenge as well. But, I'm pleased with the look so far.