Cheers all :) I made up for the gun-jumping by flagging a bit at the end of last week and getting very little done. I have been building the groundwork, but that's about all
I carved out the foamboard layer a bit more and covered it in lightweight filler. After that was halfway-set I stippled it with a stiff brush to get some more useful texture:
(click for bigger)
I sprayed the edges black (two coats of Chaos black, sanding in between because I didn't seal the MDF) and then taped them up. Then applied a couple of coats of gesso tinted with acrylic paint, in this case burnt umber and burnt siena. One of them had some dried crushed soil in it for body/texture. When the second coat was mostly dry I made clingfilm booties for the robot and stomped him around the flat area to get some very shallow hints of footmarks/
Once that had dried I mixed up raw siena, burnt siena, and burnt umber on a palette with *lots* of water and blotted various elements of this mix all over, blending and sopping up the excess with a wet brush and a paper towel. The idea was just to get some variety and lay out a little bit where the final colours are going. The packed ground behind the barricade will be lighter and browner, the piled up earth reddish, and the wet area on the front edge darker.
Last step (so far) was to airbrush less-saturated thinned blended colours (Tamiya flat earth, red brown, and deck tan in various quantities) over to flat things a bit and bring them together. There's also some olive drab on the wet bit:
While the paint was in the airbrush I misted a few passes over the feet and lower legs to provide some connection between the ground and the robot. I've since attached the concrete blocks and am waiting for them to dry - not sure how strong the glue bond will be, so I've drilled up into them from below and inserted PVA-dipped skewers to provide a mechanical bond as well.
I need to figure out a soil mix for the top layer of ground, and make/paint a load of small bits of rubbish to drift against the concrete blocks on the bumpy side. Having trouble getting into this at the moment, maybe too much work going on?