Moisture and temperature-induced stresses, arising in a clearcoat system exposed to an accelerated weathering test, were determined in order to improve the understanding of the crack formation process. Chemical degradation by water, oxygen, and especially ultraviolet (UV) radiation, induces the breaking of bonds, an increase in glass transition temperature (T_g) and the formation of hydrophylic groups. This results in a harder, more brittle, and more water-sensitive coating. In the accelerated weathering test used, the cracking is due to a static and dynamic fatigue process at steadily increasing stress levels. Changes in mechanical properties of the coatings were studied using dynamic mechanical thermal analysis (DMTA); shifts in T_g were examined by differential scanning calorimetry (DSC); changes in chemical composition were measured using Fourier transform infrared spectroscopy (FTIR). The measurements described in this article can be applied to other types of coatings and paint layer systems, and thus facilitate our understanding of the degradation process.