Qudad is an ancient lime waterproofing plaster that has been used for several millennia in the Arabian Peninsula. In Yemen, where it most likely originated, it is found on religious and secular buildings and archaeological sites. Because of its elaborate and labor-intensive application (it takes a full year to set properly), this strong, resistant material has barely been in use for the past 30 years. As a consequence, very few masons know how to make and apply it.