So after a few more weeks of work, we have a little less than half of the layout with an initial plaster shell. Once the paper shell has been primed with an oil primer, then we took a very thin mixture of plaster, dipped paper towels in it, and laid that over the paper shell.
A paper towel dipped in plaster is rather like working with a fish skin (as my dad put it). In addition, we have been playing with putting some dye in the plaster. Lesson number one on that venture was that the dark brown dye turns rather purple… and that when the plaster fully dries, the color gets a lot lighter.