Lots of scale scenes could use a simple stone wall, or a stone finish on a simple building. These instructions show you how to use various supports and model all kinds and colors of stone walls from dense insulation foams, florist's foam or styrofoam beadboard, and various protective and paintible coatings. The durability of the piece will depend on the coating you protect the foam with, as well as how much handling the piece must endure.
Although foam can easily be made into stone for walls, model horse jumps or buildings, or left to free fall down mountain terrains in railroad scenes, you may prefer more structured modelled stones from plaster, clay or paper clay. Instructions for using modelling materials to make stone finishes are given in this tutorial using paperclay to make a faux stone foundation for a porch on a rustic cottage.
I've tried to give a number of methods in the following pages for creating walls and stone buildings from a range of materials. The carving and coating methods will work regardless of whether you want a single stone wall for a model horse jump, a few stone walls for a Christmas village, building fronts for a nativity scene, blasted stone buildings for gaming terrains or scree slopes for a model railroad display.