any tips on how you got that amazing weathering.
Thanks

tbh, all the hard work is done by the properties on the oil paints - it *wants* to smear. How much it smears depends on the surface though. The interior walls are satin (slightly glossy) and the exterior walls are matt. It slides more over the satin/gloss surface (and it's easier to clean off if you mess up). The matt surface clings to the oils and you have a much shorter working time.
I use an wide brush with odourless thinners and drag top to bottom (for the interior) - the exterior was more random - and had rough oil stain washes to break up the concrete. The interiors got a faint green wash from the floor up (hold the piece upside down and let the wash flow where it wants).
You gotta get your brush dirty and try it. It practically paints itself once you get a feel for the paint.