Thanks Peter. It's 'paper' mounting card, in this case, about 1.5mm thickness, cut into rectangles to simulate the deck plates, then glued down with PVA and but-jointed. I use the same technique for doing 'concrete' or 'tarmac' dispersal areas, as it gives more depth and realism than a painted and 'lined' surface. The card can be textured in various ways, to obtain differing surface effects. I think there's a bit more detail in my Diorama Guide, somewhere here in the Modelling section.