A group of scientists* studied (.pdf) the fine structure of a termite mound. The mound was built primarily from sand and clay with a minor amount of organic material, either from the termites or soil organic material. The large grains of sand (63% quartz) are surrounded by irregular particles of kaolinite (20% clay). Larger sand particles provide the bulk of the material and the clay mortar makes the large structure cohesive. Termites add saliva to the clay during building. The saliva moistens the clay to allow the clay particles to flow and surround the grains of sand. Termite saliva may also function as a plasticizer additive that gives the structure more flexibility and resistance to cracking. Understanding the components and role of termite saliva could lead to artificial termite saliva for creating building materials from widely available sand and clay.
*Microstructure, Physical and Mechanical Properties of clayey material from termite mound: a stabilized material for adobe building. Younoussa Millogo, Mohamed Hajjaji and Jean Claude Morel. http://www.researchgate.net/publication/251527677