Investigating the performance of solid walls with water-repellent surface treatments

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A damp solid wall has poorer thermal performance than a dry wall, hence affecting its energy performance. Under future climate scenarios, the moisture content of solid walls is likely to increase, particularly due to higher rainfall intensity. Moreover, solid wall insulation changes the moisture balance of the existing wall; hygrothermal simulations often highlight the need for additional rainwater protection if internal wall insulation is to be installed.Therefore, providing rainwater protection is often necessary for solid-wall buildings that are facing higher exposure to atmospheric agents. Traditional methods include incorporating additives (e.g. tallow or linseed oil) into limewash, perhaps in conjunction with rendering and bedding mortars, which might affect the aesthetic appearance of the building, e.g. if the building was not previously rendered. On the other hand, there is some evidence on the long-term effectiveness of modern colourless water-repellent surface treatments, which would allow preservation of the aesthetic appearance of the building. If effective, these surface treatments have the potential to be an enabling technology for the improvement of the energy performance of solid-walls.Although water-repellents can have benefits, in the past, there has been evidence of the poor performance of silicone water-repellent surface treatments associated with the reduction of vapour permeability of the external surface. Recent developments in the chemical composition of water-repellent treatments are claimed to have improved this feature. However, there are uncertainties of long-term performance, particularly on building materials of different mineralogy and porosity.In a broader level, little evidence is available on the positive and long-term adverse effects of water-repellent surface treatments on building energy performance, occupants' health and durability.The research aims to investigate the long-term hygrothermal performance and effectiveness of solid walls with water-repellent surface treatments. In particular, the research will address the following research questions, which are in line with both the Technology and system performance and Comfort, health and well-being ERBE themes:1. What evidence already exists in relation to water-repellent surface treatments in traditional solid walls?2. What is the influence of these treatments on the pore structure of material usually found in external walls of traditional buildings?3. What is the influence of these treatments on the improvement of the thermal transmittance of solid walls?4. What is the long-term hygrothermal performance of solid walls with water-repellent surface treatments?5. What are the long-term adverse and positive effects on solid walls with water-repellent surface treatments?a. What are the long-term harmful and positive effects on reapplying water repellents?6. What is the influence of water-repellent surface treatments on the indoor air quality and energy performance of a solid-walled building?