Ancient Chinese mortar was made with a combination of limestone and sticky rice. Yes, sticky rice!
Recent research by Fuwei Yang, Bingjian Zhang and Qinglin Ma of the Laboratory of Cultural Relic Conservation Materials, Department of Chemistry, Zhejiang University, Hangzhou, China has shown through various analyses that limestone and sticky rice was the recipe for mortar by the ancient Chinese.
This same mortar recipe is now being used to restore ancient Chinese masonry structures which are in need of repair.
I personally found this very interesting. One of the important ingredients in sticky rice is gluten, a protein found in grains. I have several US patents on using gluten together with ceramics. It creates a very high green strength ceramics (green = unfired) so I am not entirely surprised that sticky rice was used in mortar.