One particularly interesting aspect of architectural history is that historic buildings are made from whatever materials were available in the immediate locality.   This is why we have such a rich and diverse variety of vernacular architecture.   We see this worldwide.

Earth building, and the use of earth materials, is as basic as it can possibly be.   You just need some sticky clay based material, add some cut up straw and then it can be used as a mortar for building walls or plaster for wall and ceiling finishes.   It is not unlike daub used to be used on historic timber frames.

In these pictures you can see an increasingly rare example of the earth material used for a ceiling and wall plaster.  At first glance it looks like a lime lath and plaster but it is actually an earth mix.

The ceiling material seen in these photos probably dates from the mid-1600’s, or thereabouts – with some later repairs.