Qadad

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.

The first process was repeated, this time the wall being plastered with a mixture of qadad containing smaller particles of volcanic cinders and more lime.

[10] According to archaeologist Selma Al-Radi, qadad can only be used as a plaster on buildings constructed of stone and baked brick, but it will not adhere to mudbrick, cement blocks or concrete.

In Sana'a of the early 20th century, qadad-plaster was used to line pools, reservoirs, drainage pipes, and cesspits, and to make them impermeable.

[13] Carl Rathjens, who visited Yemen in the first half of the 20th century, mentions seeing in Sana'a "the houses of well-to-do people" where the entrance halls were often painted with qadad up to a certain height.

In Islamic architecture, different consistencies of qadad were made for different usages: domes, flat ceilings, vertical walls and decorations in the geometric interlace.