AbstractThis paper aimed at studying thermal contribution to the UV ageing process, trying to understand which decisive changes reduce the protective effectiveness of polymer coatings. In this paper the effects on the shielding efficacy of different protective polymers, applied on different low porosity stones have been studied, comparing ageing of a 1000 h simulated solar UV radiation with thermal ageing at about 50 °C, which is the temperature usually reached in UV chambers. The aim of the study has been the evaluation of a possible thermal contribution: the testing methods have been suggested by UNI‐Normal Italian protocol and include capillary water absorption, static contact angles and colour variation measurements. A reduction in protective efficacy has been highlighted, probably due to both oxidation and a surface rearrangement of the polymeric material; in most cases chemical degradation of the macromolecules did not occur.