Abstract: A method for the production of an additive for building materials, wherein a hidrophobization agent is mixed with a solvent and the resulting emulsion is applied to quicklime, and then the material obtained is hydrated by adding water, wherein the hidrophobization agent is an oil having a dry matter content of 3 to 50% by weight, the quicklime in a quantity of 60 to 96% by weight is soaked with a quantity of 4 to 40% by weight of the mixture of the oil and the solvent, and after dying of the hydrated material a foaming agent is admixed thereto in a quantity of 0.25 to 0.6 part by weight of the foaming agent, preferably sodium bicarbonate, to one part by weight of the hydrated material. By using this additive, a binder comprising an additive is produced so that a hydraulic binding component and/or an isocyanate based binding component are/is added to the additive in a quantity of 4.8 to 14.8 parts by weight of the binding component to one part by weight of the additive.