The invention relates to a pasty single-component polyurethane adhesive based on at least one polyurethane pre-polymer with an NCO terminal and at least one thickener, in addition to optionally at least one additive. According to the invention, A) the polyurethane pre-polymer with an NCO terminal is substantially linear, B) the thickener is a highly disperse silicic acid in a concentration of between 2.0 and 8.0 % by weight in relation to the pre-polymer, and C) the additive constitutes less than 10 % by weight in relation to the pre-polymer. The invention thus fulfils the practical requirements for an adhesive used for construction and assembly, both in terms of fluidity and non-sag properties.