(needs more rust)
My board is meant to represent the exterior of some abandoned Ash Waste technical station. I put it together using many of the methods used in the Forgeworld Model Masterclass Vlolumn 1 book.
I used insulation foam for the raised portion, cutting through it then finishing it off by using spray paint to get a nice melted effect. Cracks were then added using Polystyrene cement which melted some more. The whole thing was then coated in a thick mixture of house paint, plaster of paris and PVA glue. Then sprinkled with sand and dirt. It actually turned out to be quite a durable surface.