The invention relates to a process for the thermomechanical surface treatment of flat webs of material, particularly those made of paper and carton, and to agents for performing said process. According to the process of the invention, adhesion between the flat web of material and the surface of the tool used in thermomechanical surface treatment, e.g., a roll or a press, is reduced or prevented by using an abhesive agent, which contains dicarboxylic dialkyl esters and/or diisoalkyl esters of C.sub.2 -C.sub.12 dicarboxylic acids with C.sub.1 -C.sub.13 n- and/or iso-alkanols as component with abhesive effect. The abhesive agent is preferably employed as an oil-in-water emulsion and is either applied to the surface of the tool used in said thermomechanical treatment or is added to the impregnating fluid or the paper coating mass or the moistening water or the steam in pre-moistening, or is applied to the paper web after the impregnating unit or directly before the smoothing roll. A steam-volatile abhesive agent is preferably used which then is metered through the steam line for steam moistening.