The invention relates to an apparatus and a method for production of additives enhancing water tightness of structural and binding building materials. The method comprises the steps of: preparing a hydrophobing agent by esterifying 60-80 m % of vegetable oil by a mixture consisting of 20-40 m % ethyl alcohol and 0.1-5 m % of methyl alcohol of the whole mass of the agent, then adding 5-30 m % agent by spraying through nozzles and water to a body of burnt lime in a reactor, and prior to adding the agent and water a mixture of 2-8 m % ethyl alcohol and 0.1-1 m % of methyl alcohol of the whole mass of the body of burnt lime is added by spraying through nozzles, while the mixture is agitating mechanically till a homogeneous mixture is prepared, then adding 40-65 m % water to the mixture, and ceasing mechanical agitating after commencement of the fierce chemical reaction.