Muralism is becoming increasingly significant in the field of urban art and a symbol of a city’s identity. The works are endangered by diverse factors including vandalism and meteorological agents, among others. Consequently, the necessity to find methods to lessen degradation such as fading or cracking emerges.

This study evaluated the physical, chemical and mineralogical changes in two acrylic fluorescent and four alkyd paints applied to concrete samples under different conditions: samples with a pre-coating and/or colour protectors (varnishes manufactured by Proa or Ega and commonly used to protect murals). Thus, six conditions (paint-only, paint with Proa, paint with Ega, paint with pre-coating, paint with pre-coating and Proa, and paint with pre-coating and Ega) were assessed. In addition, paints, concrete, and protective products were mineralogically and chemically characterized by X-Ray Diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR), respectively. A total of 36 samples were exposed to the QUV accelerated weathering test for 1512h, and throughout the test, colour monitoring was carried out. After the exposure period, a multi-analytical evaluation based on stereomicroscopy, contact angle measurement, peeling tests, XRD, FTIR and scanning electron microscopy coupled with energy-dispersive spectroscopy was conducted.

The findings suggested that the orange alkyd and fluorescent (orange and green) paints experienced the most noticeable colour changes while the green alkyd paints were the most resistant. Unexpectedly, the colour differences at the end of the test were not slowed down by the fixing primer. Using a colour protector might help preserve murals. Even though both protectors studied altered the original colour, Proa was the most effective in terms of colour reduction, but it caused more intense craquelure and the existence of tiny whitish Ti-enriched deposits.