Duration of Early Stage Drying of Aerogel-based Renders: Field Tests and Simulations in Four Swedish Cities

Paper i proceeding, 2022

Aerogel-based renders are considered as suitable solutions for energy retrofitting of building envelopes due to their energy and space-saving potentials. Their thermal conductivity measured in laboratory and dry state is within 0.03-0.05 W/(m·K) (0.21-0.35 Btu·in/h·ft2·℉), around one tenth of conventional renders. However, previous research showed higher thermal conductivities measured in field than the declared values measured in laboratory. Aerogel-based renders are wet during the early stage of application until the initial built-in moisture is dried out. This higher initial moisture content is often given as an explanation for the higher values measured in field.

To investigate the influence of the elevated initial moisture content further, the early stage drying performance of aerogel-based renders in Swedish climate conditions was studied experimentally and numerically. A section of a historical brick building in Gothenburg, Sweden, was renovated by applying a 30-40 mm (0.10-0.13 ft) thick layer of a commercial aerogel-based render. The construction was equipped with temperature and moisture sensors. Also, the exterior air temperature and relative humidity were measured. Numerical hygrothermal (heat and moisture) simulations were used to calculate the required drying time of the initial built-in moisture in aerogel-based renders. Several locations, representing different climates, and different application times of the aerogel-based render were considered in the simulations. The results of the field testing showed that a drying period longer than three months was required before the initial built-in moisture was completely dried out. According to the hygrothermal simulations conducted, a drying period of around 128-355 days could be expected for the built-in moisture in aerogel-based renders to dry out in four Swedish cities. The drying time depends on the time of application and the corresponding outdoor climate conditions during the early stage drying.