Mortar binds the stones (or bricks) together, and is also a cushion on which they lie. The mortar we can see is called “joints”. The Great Wall’s joints are convex. Most of the time, the finer the jointing, the finer the stonework, because the cutting had to be done carefully, so that the surface was smooth, and the stones fit exactly. Usually, the mortar was a mixture of lime and sand or sticky rice, depending on the region. But the first brick and stone constructions were built without any mortar. The bricks were so well jointed with lime that still today, in undamaged places, weed cannot grow.