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Qadad (Qadâd, Kʉðað) or Qudad is a waterproof plaster surface, made of a lime plaster treated with slaked lime and oils and fats. The technique is well over a millennium old and can be used as a roof covering.
Volcanic ash, pumice or other crushed volcanic aggregate are often used as pozzolanic agents.
Due to the slowness of some of the chemical reactions, qadad mortar can take over a hundred days to prepare, from quarrying of raw materials to the beginning of application to the building. It can also take over a year to set fully.
In 2004, a documentary film Qudad, Re-inventing a Tradition was made by the filmmaker Caterina Borelli (preview). It documents the restoration of the Amiriya Complex, which was awarded the Aga Khan Award for Architecture in 2007.