Sodium sulphate weathering and the disintegration of Mohenjo-Daro,Pakistan

In Pakistan various brick building structures are currently disintegrating in the Indus Valley. These include the Harappan site of Mohenjo-Daro. The environment of this site is described, the nature and speed of the disintegration problem is outlined, and the cause of disintegration is discussed Weathering occurs in association with the development of salt efflorescences and some bricks disintegrate only a few years after being laid down. Chemical and X-ray diffraction analyses show that the predominant salt is the sodium sulphate mineral thenardite. The reasons for its effectiveness are discussed. They include its high solubility, the rapid change of solubility with temperature, and its hydration characteristics.