My state (Maine and formerly MA) does allow cob structures, as long as they will have some type of on or off-grid wiring/plumbing that can be inspected, and you can prove they are safe/load bearing with architectural plans. They do need to have at least some light straw or full straw bales added for R-factor insulation, since the winters up here are very cold though. It is wild to me that so many states are still making this harder than it needs to be for people.

There is actually an awesome company I learned about while doing a Tadelakt workshop a couple years ago. The teacher, who had years of natural plasters/finish experience highly recommended it as a simpler alternative that was still Earth friendly. It holds up well, but costs a bit more than the alternative. It is called Earthhaus. They make all kinds of completely natural, non-toxic pigments and washes from only minerals that are totally beautiful. If, for example, you wanted to just do a lime wash over something, they have a whole range of softer colors. It is so pleasant to work with, and easier IMO than the old fashioned way of doing both lime plastering and Tadelakt finishes. Here is their website, in case it might help anyone: https://earthausplaster.com/

I think once you add cob to everything, it might shift underground with these. The cob is really heavy. I am not sure where you are located, but here in New England with all the rocks and frost heaves, this definitely wouldn't work with cob. It might be ok for something like a deck though.

What if you used some coffee and some sand? Would that help to keep bugs away, but also if the coffee breaks down, you would still have some structural integrity? I wonder if you could build something small, like a mini-oven or mini hut this way to test it. Please let us know how it holds up if you do. I think this is a terrific idea!

I was also thinking of building a hobbit cobin into a hill, but am not sure it will be a good idea in this climate. Here in Maine, it is pretty damp with lots of frost heaves in winter. I know Earthships don't usually work without getting mold problems up here. I am thinking cob might have some of the same issues. Has anyone done this in Maine or New England or Eastern Canada without mold/mildew issues underground?