Qadad

After collecting blocks of lime stone, they were fired in a kiln for 4 days, after which the fire and baked lime were extinguished with water, and allowed to cool for 2-3 days more. The baked lime (Arabic: nūreh) was then crushed and mixed with soft, black volcanic cinders known as scoria (Arabic: shāsh), a pumice having the consistency of gravel.[9] The scoria and lime were pounded with a stone to break them down into finer particles and thoroughly mixed together without water (the two ingredients being mixed together in a ratio of two parts of aggregate to one part of lime),[3] and then allowed to rest 3-4 days until settled. Afterwards, the two elements were mixed together with water (usually 1 volume of water to 3 volumes of lime/aggregate), during which time the batch is continuously agitated in a tedious process known as slaking and which required many long hours of manual labour (as much as 4-5 weeks), before a finer lime water solution was added thereto for 1-2 months so as to convert it to a paste. The more that it was pounded with a long shovel or wooden paddle, the more the qadad became adhesive.[9] With the now ready mixture of lime and volcanic cinders, they would apply three-layers of qadad-plaster to the walls of cisterns to make them impermeable; the first layer having the largest particles of volcanic cinders (scoria) and the least amount of lime was applied to rough stone, the plaster being added to a thickness of about two inches. They took a sharp-edged stone and, for several days, pounded and rubbed the first layer of qadad firmly onto the wall, all the while sprinkling it with lime-water to keep it wet.[9] The second layer was applied after fully working the first layer by beating. 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. A sharp-edged stone was again used to pound the qadad firmly onto the wall, all the while sprinkling it with lime-water to keep it wet. Finally, the third layer was applied containing the smallest particles of volcanic cinders and the largest quantity of lime and worked with a sharp-edged stone (one part aggregate to two parts lime, and pounded to a fine paste), and lime-water spattered on the wall to maintain its wetness.[3] After the final application, the wall was treated with a very finely-ground consistency of qadad which was allowed to dry, and when dried, an application of animal fat (suet) was then smeared on the wall for smoothing and burnishing.[9] The end result is that of a wall that is as hard as smooth-marble with beating.[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.[3] In Yemen it was traditionally made with two basic ingredients, baked lime and volcanic scoria, other countries have traditionally made-use of fine riverbed sand or pebbles instead of scoria, and which were mixed together with lime for use as a common mortar,[3] or to be used as an impervious wall plaster.

Ashrafiya Mosque in Taiz is covered with Qadad.[11]

Mudhaffar Mosque in Taiz covered with Qadad[12]

A house in the historic Town of Zabid covered with qadad carved into yeseria

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.[9] After applying the qadad, the coating was burnished with a stone.[9] Often its use extended unto the main kitchen room and to gutters and sinks, wherever water was likely to be used extensively[13] (see also tadelakt). The walls of store-rooms where grain was kept and which required being impervious to water were also frequently painted-over with qadad and which gave to the rooms an appearance of being painted with oil paint.[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.[13] The interior walls of public baths were sometimes brick, sometimes stone. If brick, they were protected with a thick layer of hard gypsum plaster which were then oil-painted.

In Islamic architecture, different consistencies of qadad were made for different usages: domes, flat ceilings, vertical walls and decorations in the geometric interlace.[14]

Wikimedia Commons has media related to Qudad.

• Limepit (old technique used in calcining limestone)
• Lime plaster
• Plasterwork
• Pozzolan
• Tadelakt, a similar waterproof lime-soap plaster
• Sarooj, a similar water-resistant plaster

• Caterina Borelli, Caterina Borelli: "QUDAD - reinventing a tradition - English version" on Vimeo, 2012, A Documentary on the renovation of the ‘Amiryia Madrasa and Mosque in Rada, Yemen, using the ancient waterproofing technique with qudad.