Keep in mind that clay bodies are different, clays like bentonite will have vast resistance to water drops or rain. You migh find the appropriate clay pits in your area, and most of the time sealant clay has a very light pastel color. I tested red clay vs a kaolin/bentonite clay cob brick and the endurance of the second block spent a year exposed to a few hurricanes and yearly rain and it lost less than 1% of uta volume. I used a heavy clay/sand/straw mix 1:1:2 by volume made for thermal mass and it seems that you want to prioritize insulation.
