Wetting and drying of aerogel-based coating mortars in Swedish climates
Doctoral thesis, 2023

Aerogel-based coating mortars (ACMs) have emerged as energy-efficient wall finishes with thermal conductivities of 30–50 mW/(m∙K). These coating mortars represent a promising alternative to traditional thermal insulation materials for retrofitting uninsulated building envelopes particularly in culturally significant structures. Although previously used in Central Europe, their moisture absorption under rainwater wetting, early-stage drying, and long-term hygrothermal performance in other climates remain inadequately explored. This gap in knowledge presents challenges in designing moisture-safe solutions and evaluating in-field thermal insulation performance in regions characterized by high moisture loads and limited drying potential.

Therefore, an investigation was conducted to increase knowledge of the moisture performance of coating systems with ACMs. This investigation combined field and laboratory-based measurements with numerical hygrothermal simulations to study their moisture absorption under diverse wetting scenarios and evaluate their drying performance. Furthermore, the impact of surface water-repellent properties and surface cracks was assessed. The laboratory studies employed a newly developed small-scale test setup designed to simulate runoff wetting caused by typical wind-driven rain intensities in Sweden. Moreover, two supplementary capillary suction experiments under zero (free suction) and elevated hydrostatic pressure (created by Karsten tube) were conducted to explore additional wetting scenarios. A 15-month field test in Gothenburg, Sweden, combined with hygrothermal simulations were utilized to evaluate the early-stage drying and long-term hygrothermal performance of the coating system with ACM for four Swedish cities.

The laboratory measurements demonstrated minimal moisture absorption in the undamaged coating system with ACM, even during prolonged 24-h runoff wetting. As expected, applying water-repellent paint (sd = 0.01 m) to the exterior of the coating system effectively reduced the water absorption while maintaining the drying capacity. Conversely, coating systems with a 1 ± 0.5 mm wide surface crack had 3–5 times amplified water intrusion due to hydrostatic pressure from the created water film on the surface. This could increase the risk of local moisture accumulation. Capillary suction tests of the ACM revealed a substantial increase in water absorption after repeated wetting exposure. Meanwhile, the same tests on the complete coating system showed a consistently stable water absorption. Field measurements indicated that the built-in moisture in the ACM dried out within six months. Hygrothermal simulations for four Swedish cities revealed an early-stage drying period ranging from 134 to 336 days based on the climate and time of application. Over time, the ACM exhibited no hygroscopic moisture accumulation; however, walls highly exposed to wind-driven rain could experience elevated relative humidity within the ACM, thereby resulting in an average increase in thermal conductivity of up to 9%. The findings show that the examined coating system with ACM presents a moisture-safe solution for retrofitting external homogenous concrete and masonry structures, preventing moisture accumulation from rainwater wetting. However, considering the information regarding the anticipated early-stage drying time and the moderate elevation in thermal conductivity is crucial when evaluating the in-field hygrothermal performance of the coating system.

runoff

Aerogel

retrofitting

coating mortar

wetting

drying

wind-driven rain

render

SB-H5
Opponent: Professor Nathan Van Den Bossche, Ghent University, Belgium

Author

Ali Naman Karim

Chalmers, Architecture and Civil Engineering, Building Technology

As building regulations have evolved to demand greater energy efficiency, there is a growing need for retrofitting older buildings, including heritage buildings. Many of these structures already today have moisture-related issues, making it crucial to find energy-efficient and moisture-safe retrofitting solutions. However, it is not just about improving energy performance or moisture safety - it is also about preserving the unique appearance and character of culturally significant structures. These heritage structures often have strict rules governing any changes that might affect their historical aesthetics. This is where aerogel-based coating mortars (ACMs) can come into play, offering outstanding thermal insulation properties that can potentially replace both traditional coating mortars and insulation materials such as mineral wool.

Despite their potential, ACMs remain relatively unexplored in Scandinavian countries like Sweden. To ensure their successful adoption, we must understand how they perform in the local conditions, especially in terms of moisture resilience. However, currently there is a knowledge gap regarding the fundamental properties of ACMs, such as watertightness under rainwater wetting and drying performance at early stages. Closing this gap is essential for developing moisture-safe designs and accurately predicting ACMs' thermal performance in real-world applications.

This thesis aims to contribute towards bridging this knowledge gap and provides insights into the practical applications of ACMs in the Swedish context. The thesis comprises experimental and numerical results obtained from a field test in Sweden, along with a tailor-made small-scale test setup. The latter is developed to evaluate the moisture performance of wall assemblies when subjected to realistic rainwater runoff based on typical wind-driven rain intensities in Swedish climates.

Super insulation render for renovation and new constructions

Swedish Energy Agency (2018-006152), 2019-01-01 -- 2021-12-31.

Super insulation plaster for sustainable renovation

Swedish Energy Agency (P2022-00872), 2022-11-01 -- 2023-12-31.

Subject Categories

Civil Engineering

Other Civil Engineering

Building Technologies

ISBN

978-91-7905-925-5

Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 5391

Publisher

Chalmers

SB-H5

Online

Opponent: Professor Nathan Van Den Bossche, Ghent University, Belgium

More information

Latest update

2/28/2024