Climate change and the greening of masonry: implications for built heritage and new build

Lead Research Organisation: University of Oxford
Department Name: Geography - SoGE

Abstract

SUMMARYThere is increasingly compelling evidence that stone decay environments vary significantly across the British Isles, and that these climatic and pollution regimes are themselves changing as, for example, climate itself changes, sulphur emissions are reduced and local levels of atmospheric NOX rise. Because of this there is an urgent need to review the changing nature of decay processes, investigate the new, and developing, environmental conditions that are driving these changes and to scope their impacts on the future decay of masonry materials and any required modifications to specification and remediation strategies. Nowhere is this need more apparent than in the northwest of the UK. The fact that building stones, especially sandstones, already react so adversely and so rapidly to the moist, often salt rich environments found in this region (Smith et al. 2002), must inevitably raise fears of what could happen as a consequence of any increase in their time of wetness associated with projected warmer, wetter and possibly longer winters. In short, in response to changing climate and pollution it is likely that we will have to radically rethink our understanding of masonry decay and conservation.Quartz sandstones have been chosen to investigate these issues because they have proven to be susceptible to, and highly sensitive indicators of, subtle changes in moisture and temperature regimes, as well as pollution conditions. They also provide acid, open-textured conditions that favour algal colonisation. If stonework were to remain wetter for longer and not dry out either as frequently or as thoroughly as before, there are a number of physical and chemical effects that could be hypothesised. These include: the deeper penetration of salts (especially those of high mobility) and increased biological colonisation leading to active biological decay, both chemical and physical, as well as unsightly soiling of buildings that is expensive to remedy.This project will therefore build on earlier research into sandstone decay processes to investigate the likely impacts of predicted climate change on future decay. To do this, it will concentrate on the effects of changes in moisture regime on quartz sandstones. This will combine laboratory simulations with environmental monitoring and the assessment of decay patterns related to conditions of exposure on selected sandstone buildings, linked to sampling and analysis of complete stone blocks. Central to this is the construction of test walls in a wet environment in the west of Northern Ireland with embedded sensor systems to monitor thermal and moisture regimes linked to biological colonisation. This will be validated against laboratory investigations of the colonisation process and the feedbacks that could affect stone decay, together with investigations of ion diffusion associated with prolonged 'deep wetness' of masonry. Because of the detailed knowledge already possessed by the partnership, and the access to buildings undergoing renovation provided by the industrial collaborator, environmental monitoring and sampling will concentrate across Northern Ireland, supported by limited selective sampling of sandstone structures in Scotland and northwest England.Underpinning all investigations into stone per se, is the statistical downscaling of national and regional climate change scenarios, linked to measurements of stone condition and the factors controlling it. This novel approach is essential at a much wider scale if such scenarios are to be successfully translated into meaningful strategies for adaptation to environmental change.

Publications

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Description Algal greening and moisture regimes in sandstone walls have been found to be complex and dynamic. Using a combination of field measurements on historic sandstone walls in Belfast, monitoring of test walls at Derrygonnelly and a series of small-scale field and laboratory experiments we have investigated the nature, dynamics and impacts of algal greening and deep-seated wetness on the deterioration of a range of building sandstones. Using innovative 2D resistivity surveys of historic sandstone walls in Belfast we found very patchy coverage of algal greening, and no evidence that such greening is correlated with, or causes, wetter conditions in the immediate sub-surface zone. State-of-the-art molecular methods have been used to characterise the biological communities within the green areas - finding higher diversity than expected, with a relatively homogeneous group of algae and considerable fungal diversity across different walls and

sample areas. Slow development of algal greening on the Derrygonnelly test walls precluded more detailed observations within the timeframe of the project, but the developing communities can be studied in future. Field experiments using smaller blocks and architectural elements (balusters) illustrated the importance of aspect and slope angle to the rate of greening. Laboratory experiments under highly controlled conditions showed how algal greening is 'fine-tuned' to the amount of surface moisture present - both too much and too little moisture retards growth. 2D resistivity surveys of Belfast walls also revealed several instances of deep-seated wetting, with areas 20-30cm inside the stone surface appearing highly wet. Patchy moisture regimes were the norm. Monitoring of wetting and drying on the Derrygonnelly test wall site further illustrated the importance of aspect, and the non-linear progress of wetting. Only after long wet periods did the moisture front penetrate far (> 20cm) into the walls, predominantly on the exposed, SW-facing side, with very slow drying. Statistical downscaling of GCM data shows that such wet periods are projected to increase in the coming century, though the magnitude of this increase varies across NW UK. Laboratory experiments, carried out over 2 month periods, show the importance of diffusion of ions under saturated conditions and the complications introduced when mixed salt solutions are used. Very high pHs were found in some experiments (> 10), indicating that mobilisation of silica could be an important weathering process under conditions of deep-seated wetness. In sum, our multidisciplinary, multi-method study has demonstrated the complexity of responses of sandstone facades (historic and new build) to prolonged heavy rainfall. Algal greening has not been found to directly influence surface deterioration, but may act as a signal of altered moisture regimes which in turn have the potential to induce deep-seated chemical transformations likely to make sandstone more vulnerable to deterioration (because of mobilisation and patchy re-precipitation of silica). Our research has involved the development of many innovative techniques for monitoring moisture in walls and characterising algal communities and their impacts (several of which are available to view on the internet as a result of additional EPSRC Pathways to Impact funding). There are several practical implications of our research, which have been discussed with our external advisory panel and further disseminated through two linked EPSRC-funded Knowledge Transfer Scheme activities. Firstly, algal greening has been shown to be less directly damaging than commonly thought, and KTS work with Historic Scotland has included this information in improved INFORM guidance notes for practitioners. Secondly, KTS work with S McConnell & Sons Ltd on surface treatments has shown some to be effective on porous sandstones, delaying water uptake, and potentially reducing moisture-driven decay.
Exploitation Route Both algal greening and deep seated wetting can cause problems for conservators and architects managing sandstone buildings. Our findings can help their decision-making, by providing advice based on our integrated field and laboratory programme. Furthermore, our findings can be taken forward by those wishing to develop optimised techniques for measuring moisture in walls and determining its impacts on deterioration and algal colonisation.
Sectors Construction,Environment

URL http://www.qub.ac.uk/schools/ClimateChangeandthegreeningofmasonryimplicationsforbuiltheritageandnewbuild/Project/
 
Description Our research findings have been used by a KE project with Historic Scotland to develop updated briefing on greening and deterioration; and as the basis of a workshop on non-destructive techniques for diagnosing moisture and other problems in masonry walls. Furthermore, our findings have led to longer term collaborations with Consarc Design and Historic Scotland, to provide better toolkits for monitoring moisture dynamics in masonry walls.
First Year Of Impact 2012
Sector Construction,Culture, Heritage, Museums and Collections
Impact Types Policy & public services

 
Description Consarc and Stone Conservation Services 
Organisation Consarc Design Group
Country United Kingdom 
Sector Private 
PI Contribution Research on the implications of climate change for algal greening and deep wetting of stone masonry
Collaborator Contribution Contributing design and conservation advice, including designing the test walls; providing access to database of stone deterioration acorss northern Ireland; advice on how to make our findings relevant to practitioners
Impact Project workshop April 2012 and associated online resources. Collaboration is multi-disciplinary, involving architects, engineers, geologists, geomorphologists, climatologists and ecologists.
Start Year 2009
 
Description Consarc and Stone Conservation Services 
Organisation Stone Conservation Services
Country United States 
Sector Private 
PI Contribution Research on the implications of climate change for algal greening and deep wetting of stone masonry
Collaborator Contribution Contributing design and conservation advice, including designing the test walls; providing access to database of stone deterioration acorss northern Ireland; advice on how to make our findings relevant to practitioners
Impact Project workshop April 2012 and associated online resources. Collaboration is multi-disciplinary, involving architects, engineers, geologists, geomorphologists, climatologists and ecologists.
Start Year 2009