Weathering Question

[DocGeoff]

I want to weather a repair shop/gas station. Normally I use powers and dry brushing, maybe other stuff, but this time I want to airbrush a general weathering, like the accumulation of dust & dirt and age from sitting on the corner for the last forty years... Any suggestions of colors to mix. I use water based paints like Model Flex mostly.
Thanks for the input (I hope),

[tom mann]

Start with Polyscale Dirt, and spray it straight about a foot away.  You'll be amazed how it fades the model and how it removes any glossyness.  If you need to go lighter, spray a white/earth mixture.