An assessment of adhesives for the re-adhesion of flaking acrylic paint on outdoor murals

Abstract

Outdoor murals are typically subject to deterioration due to a number of reasons, including environmental factors, which may lead to phenomena such as flaking of paint. To date there have been few studies regarding the remedial intervention to treat such deterioration phenomenon on modern outdoor murals. The stabilization of this is typically performed using an adhesive, which aims to re-adhere the flake to the support. This dissertation assesses six adhesives for the re-adhesion of flaking acrylic paint on outdoor murals, with the focus on a case study: the acrylic-based Market Street Railway Mural in San Francisco, California. The general criteria for the intervention of re-adhesion were considered prior to establishing the site-specific performance criteria and working properties of adhesives. After testing on site, the selection of adhesives was shortlisted and Rhoplex AC 2235M (applied on site), Primal AC 35 and Paraloid B72 were further tested and analysed in the laboratory. The laboratory study made use of samples in order to test properties such as adhesion (bond-strength), adhesive deposition (SEM), flexibility and elasticity, hygroscopicity and glass transition temperature (Tg). The working properties of the adhesives were assessed both on site and more in-depth in the laboratory through flow test and surface tension test on the liquid adhesives. The results showed that Rhoplex AC2235M displayed the overall most suitable performance including a Tg within the desirable range for the specific case study. Primal AC35 generally showed to be suitable on many points, however one major drawback was its low Tg. Paraloid B72 did not show satisfactory results, due to generally poor performance and working properties, proving not to be suitable for the purpose of this research.