Abstract: A method of incorporating a material in a settable binder is disclosed. The binder includes a source of caustic magnesium oxide. The method involves mixing the material with the binder, either as part of a slurry or for subsequent formation into a slurry, and then adding a setting agent to the slurry. The Setting agent is added to enhance setting of the binder. The material can be a hazardous waste material or components thereof. The inventors have surprisingly discovered that when the setting agent is added after mixing of the material with the binder, that a superior setting of the material in the binder can be achieved. The settable composition can comprise only a caustic magnesium oxide binder and a setting agent for the binder, as the inventors have surprisingly discovered that there is no need for any other binding agents, thus providing a simpler binder composition and method of use.