I hate to show my ignorance here, but how does using glutenious rice make it possible for ancient structures to still be standing?
Maybe the worker-slave puked into the mortar mix after he consumed the rice porridge.
I can't tell you how it works, but I have a small tin of rice paste and I can vouch for the fact that any bond made with it is permanent. It's every bit as strong as Gorilla Glue without the mess.
Maybe it serves the same purpose as the adhesion additives that are sometimes added to mortar and concrete mixtures here in the states. I don't know the exact formulation, but it looks and smells exactly like plain old Elmer's white glue. The additive, the instructions say, helps the mortar or cement stick to existing masonry work. I suppose it seeps into microscopic voids in the surfaces of existing masonry planes and creates a mechanical bond. In the old days, bricklayers and cement workers would mix a thin concoction of cement and water and paint it into crevices and pockets of existing structures before troweling in the concrete or mortar as the project dictated. That would be my guess.