Khalili in California for further research into earth architecture. Each of his projects achieved moderate publicity, but Khalili's geltaftan technology has seen little use since the 1980s. This is in part because of the pollution involved in oil firing. The Geltaftan Foundation, and Cal-Earth has since carried on experiments with ceramic housing, but Nader Khalili is most noted today for his work developing Super Adobe: an earth building technique using earth-filled bags as structural elements. Building and firing The earth used for building ceramic houses is essentially a type of adobe with a higher clay content and fewer impurities. The earth and water are mixed until the substance has "the consistency of bread dough" The clay/earth mixture is worked into forms, and the blocks dry over a period of one to two weeks. A mortar is made with a "flux" (glass, soda, or colmanite) to help fuse it. The adobe blocks are laid so that the joints are staggered. There is no mortar in the vertical joints to allow for expansion and contraction during firing. Rammed Earth and Mud Pile can also be fired, but must be fired from both sides because of the thickness of the walls. Building with stiff wet mud, like a potter, allows for thinner walls, and the possibility of incorporating flue systems into the walls. Arches can be formed by stacking non mortared blocks as form work, and removing them after firing. The firing system used is based on the availability of fuel and local know how. In Iran, village kilns used oil for fuel, so a simple, gravity flow oil burner could be used to fire each room. Flues are created (either integrated into the structural, or made for removal) and openings are closed with un-mortared brick. Joints are covered with a thin layer of mud plaster. The burner is placed at a low opening with room for air circulation, but protected from wind. During the early stages of firing, water vapor escapes through the flues located on the roof. Once the steam escapes, roof flues can be closed and heat will circulate the room before escaping from floor vents. This is when the room is heated to at least and the adobe is baked. After the firing, only the ceiling flues are opened to allow slow cooling over at least 48 hours. The outside walls are finished with either a mud straw plaster,