Abstract: A plastic refractory material or a refractory mortar which harden when dried and which contain at least one light-weight filler, a binder, fibers and/or wollastonite as well as water is characterized in that blown closed-cell volcanic ash is used as the light-weight filler, the ash being provided with a superficial water-protection layer, in that an inorganic-organic hybrid binder is used as the binder, the binder containing silicic acid and an organic polymer, and in that the material or the mortar contains kaolin or kaolinite and silicon dioxide. It is suggested to publish the abstract without a drawing.