Sarooj is a traditional water-resistant mortar used in Iranian architecture, used in the construction of bridges, and ice pits or earth refrigerators (yakhchal).
It is made of clay and limestone mixed in a six-to-four ratio to make a stiff mix, and kneaded for two days. A portion of furnace slags from baths is added with fiber Louis (egg and straw) is added and newly fixed, then beaten with a 10 cm wooden stick for even mixing. Egg white can be used as a water reducer as needed.
References
Sarooj Wikipedia(Text) CC BY-SA