Knowledge gaps regarding the hygrothermal and long-term performance of aerogel-based coating mortars

Aerogel-based coating mortars are an emerging class of multifunctional wall finishes that stand out for their thermal insulation performance. Commercial and trial mixtures, studied under laboratory conditions, have a declared thermal conductivity of about 30-50 mW/(m center dot K). This is comparable to conventional insulation materials such as polystyrene and mineral wool. Aerogel-based coating mortars are primarily intended for use in existing and uninsulated building envelopes. Currently, there is a high research interest in the development of aerogel-based coating mortars. Nevertheless, the knowledge about their hygrothermal and mechanical properties have not been fully explored yet. These properties are needed to assess the moisture risks and long-term durability in different applications and to justify the higher investment costs for aerogel-based coating mortars compared to conventional ones. Apart from the material properties of aerogel-based coating mortars, results from full-scale studies focusing on hygrothermal performance are scattered and representative for limited number of climate conditions and specific products. In this article, available information on hygrothermal and mechanical properties of aerogel-based coating mortars is collected and systematized. The aim is to map the missing data needed for moisture risk assessments. This study focuses on knowledge gaps regarding the hygrothermal and long-term performance of aerogel-based coating mortars, both commercial products and laboratory-based trial mixtures. In addition, economic perspective and health related concerns of the material are discussed. The results indicate that future research efforts should focus more on moisture risk assessments of the material to ensure moisture safe designs especially in areas with humid climates and freeze-thawing. More information needs to be readably available on the mechanical and hygrothermal compatibility of aerogel-based coating mortars with other materials in multilayer wall systems. In addition, available information on the hygrothermal and mechanical properties and long-term performance of aerogel-based coating mortars need to be further explored.