The present invention provides a process to prepare a powdery additive suitable for improving adhesion of building material compositions to substrates having a surface energy of 50 mJ/m2 or lower, measured according to DIN 5660-2:2011-12, the additive comprising a polysaccharide and a plasticizer, wherein the plasticizer is liquid at 50° C. or lower, has a boiling point of 100° C. or higher and is selected from a specific group, comprising the steps of a) admixing the plasticizer to an aqueous medium of the polysaccharide followed by the subsequent drying of the admixture, or b) preparing a first particle comprising the plasticizer by (i) adsorbing the plasticizer onto a carrier, or by emulsifying the plasticizer with a synthetic water-soluble polymer in water and subsequently drying the emulsion, and (ii) mixing this first particle with a second particle comprising the polysaccharide wherein the mean particle size of the coarser of the first and second particle is not more than 10 times the mean particle size of the finer particle, or agglomerating the first and second particles into one particle. The invention further provides the additive obtainable by this process, use of the additive and building material compositions containing the additive as well as a process to adhere such compositions to substrates having a surface energy of 50 mJ/m2 or lower.