Resistance to artificial daylight of paints used in urban artworks. Influence of paint composition and substrate

Abstract

Solar radiation is one of the deterioration factors par excellence of modern urban artworks, as among other manifestations, it causes loss of colour. This deterioration can compromise the durability of the works, although it is not known to what extent this durability can vary depending on the substrate supporting the paint. We evaluated the susceptibility to sunlight of 10 paints of differing compositions as typically used by urban artists, by exposing them, applied to concrete and brick, to artificial sunlight ageing test in laboratory conditions. Colour changes over time were studied, along with mineralogical (x-ray diffraction), chemical (scanning electron microscopy-energy dispersive x-ray spectroscopy) and physical (contact angle and peeling tests) changes. The durability of the paints on these substrates depends mainly on the paint composition (base, pigment and filler) but also on the type of substrate, as this influences paint adhesion capacity. The greatest colour modification was detected in fluorescent paints, which lose colour due to degradation of the organic phase, and with aggravation of defects during drying, eventually detach from the substrate.