I would never even consider hay in a building under any circumstances. It’s food therefore will attract ants ,termites and god knows what. Straw is basically silica it’s typically from the second cutting and has no grain. If you’re doing bale cob and using cob to sandwich bales you may want to build a mock wall and use a moisture meter. Clay is water greedy and you will see how it can wick untold amounts of moisture into the center of your walls where it is sequestered and cannot easily dry out. Mold and rot may occur
