The effect of a protective layer on the optical behavior of retro-reflective paintings for building envelopes

Retro-reflective (RR) materials, applied to building envelopes, constitute an option to tackle Urban Heat Island phenomenon, thanks to their capability to reflect the sunlight predominantly towards the solar incidence direction. RR coatings are obtained with the deposition of glass beads on traditional diffusive materials. During their lifetime, outdoor aging and soiling affect their optical behavior. In addition, without a proper protection, some glass beads could detach from the paint and disperse in the environment. Hence, a necessity arises for the application of a safeguarding stratum on RR materials to avert the separation of glass beads in RR coatings following the aging process. In this paper, five RR samples were produced, employing a highly reflective paint as foundation, RR glass beads and a protective layer. A diffusive sample, without glass beads, was made for comparison. Samples underwent spectrophotometric and angular distribution analyses. The effect of the protective layer on the optical behavior was assessed comparing the results with those obtained for the same RR materials without the protective layer. RR samples with a protective layer exhibit a higher reflectance with respect to the same RR sample without a protective layer. In the near-infrared (NIR) region, a lower reflectance occurs for all RR samples with a protective layer. A less concentrated angular distribution of the reflected light was observed for all RR samples with the addition of a protective layer.