Our house (in Spain) is 200 years old, and built w. Cobb and rocks, traditional Spanish style. Most of the walls are plastered, but in the living room we have opened up some of the wall bc we think it is so beautiful. However it needs care... the cob is crumbling and falls of bit by bit. So how do I care for it? And how do I seal it, without covering the beautiful stone work, so that it doesn't continue to crumble?
That wall was probably meant to be plastered, and the coating was what gave the surface integrity. If you really want to see the stones, you will need to get creative.
If you're brave, you could mix a rather dry grout of sandy cob and press that into the voids as firmly as you can. Before it's completely dry, take a damp sponge and go over the area to clean the surfaces of the stones and fill all the voids with cob grout. Try this on a small patch, because it might not work and you may need to cover it with a lime plaster after all. See how this turns out, and if you like the effect then do the whole wall. When it's done, give it a coating of flour water to keep the cob from dusting and flaking off.
It depends on how much clay is in your soil. You just want enough clay to hold things together. Too much will shrink and crack as it dries. Start with a test area to get a feel for it and you can adjust the mix as you learn the properties of the material.