Inspired by the new Frary video, I tackled the back corner where some topography goes. I've taken a lot of photos and will go back and do a more comprehensive build, but I wanted to get these out. Basically, there's styrofoam, rough shaped and then painted with Zinzer primer (to provide better adhesion. Then I covered the painted styrofoam with nylon self-stick wallboard tape, allowing me to adjust the contours and providing a really sturdy underlayment. 2 layers of plaster wrap followed, and that gets us to this point, where I'm test-fitting rock castings:
Then I grouted the castings into shape with sculptamold*:
A spray of ink and water brings out a lot more relief:
You can see that I used two different kinds of plaster for the castings. I prefer the Woodland Scenics Lightweight Hydrocal, which is the hard stuff at the base. The other castings are done with conventional plaster of paris.
There's white paper taped over the photo backdrops, by the way...
* AC Moores carries Sculptamold, a great use for a 50% off craft coupon.