Ianto Evans of the Cob Cottage Company of Oregon has a web site that you should visit if you are interested in cheap housing and a long tussle with the authorities who control how those in a free country may build. Flemming Abrahamsson runs a small company in rural Denmark, thatching and making stoves and eco-toilets. Ianto, on the left, is explaining how to embed a window as the wall is built. I made some tiles from sand, clay and straw. These were air dried and then put to the test as a humidity buffer for museums, or anywhere else.
Mud works well.
The purple line is the RH of a room at 25 degrees, with one third of an air change per hour, and with no absorbent surfaces. The brown line is the same room with 30mm of mud on the walls. The graph shown above is a computer simulation, based on a much shorter period of measured results from a climate chamber. Now researchers are beginning to translate this 'feel good' factor into physical constants quoted in SI units to many decimals, so maybe there is some chance that we will soon be making public buildings out of the stuff that sticks to our boots. There are many building materials that are porous and water absorbent in varying degree.