Aerogel-based Coating Systems in Swedish Climate: Early-Stage Drying and In-Situ Thermal Conductivity

Paper in proceeding, 2025

Aerogel-based coating mortars (ACMs) are energy-efficient coating systems with thermal conductivities of 0.03-0.05 W/(m-K) (0.21-0.35 Btu in/h ft² °F). This work investigates the early stage drying of a fresh ACM-system used as exterior render in a moderate and humid climate. Temperature and relative humidity within a 40 mm (1.57 in) thick ACM applied on a brick masonry wall in Gothenburg, Sweden, were monitored over 15 months in the field. Additionally, the moisture-dependent thermal conductivity of the same type of ACM was measured in the laboratory using the transient plane source method. The field measurements showed that the built-in moisture dried out within approximately six months, with no subsequent accumulation. In the laboratory conditions, thermal conductivity increased by up to 13% within the hygroscopic region, i.e. from the absolutely dry state to 80 % relative humidity. Fully saturated laboratory samples, however, showed conductivities 10 times higher than the declared value. By combining the field moisture data with the laboratory results, it was found that the in-situ thermal conductivity during the first 3-4 months was 5-8.5 times higher than in the dry state. A fter drying, it stabilized at about 10% above the declared value. These findings highlight the need to account for 3-6 months of initial drying in similar climates. For long-term evaluations, thermal conductivity around 10% above the declared value should be considered. Future work should include extended monitoring, especially on facades exposed to wind-driven rain.