Q: I like the idea of gravel bags (double-bagged) for the stem/foundation wall on top of a rubble trench, seems very simple and straightforward. But how do you finish them? Since they would be in contact with the ground (and water), I'm guessing not with an earthen plaster. So would you use lime - or cement - plaster then? Would this stem wall need wire for such a plaster to hold onto? And if you wanted to use an earthen plaster for the rest of the building, would you need some sort of edging or lip for it to rest on and separate it from the stem wall below, so moisture couldn't migrate up the outside of the wall?

A: You are right that a stabilized plaster with either cement or lime is a good idea for a stem wall foundation, and using a stucco mesh is also a good idea. I don't think it is customary to place an edging between stabilized plaster and earthen plaster. I might suggest that you bevel the top of the stem wall plaster, so when you apply the earthen plaster it overlaps just a bit, like a shingle does. This should at least discourage moisture from draining behind the lower plaster.