Track 3: DELIVERY – INTERVENING INTO HISTORIC PLACES / Volet 3 : Réalisation – Intervenir dans les lieux historiques

Designing and evaluating repointing mortar mixes for highly exposed and damp historic buildings (church towers) in South-West England

Saturday, October 14
10:45 AM - 12:15 PM

Many historic buildings of architectural significance, especially churches, are highly exposed to harmful environments, such as wind and driving rain. Moisture is one of the most common agents in the deterioration of building materials, leading to biological growth, salt damage, and dampness, that may have negative effects on the inside conditions. To ensure preservation of historic masonry, rain penetration needs to be mitigated. This is one of the main roles of mortar in the masonry joints. To cope with a specific environment, mortars can be tailor-made by choosing appropriate compatible materials to enhance some key properties. For example, a pointing mortar to deal with rain water ingress would ideally have a combination of high permeability to draw moisture out of the wall, and should be more porous than the surrounding stones, removing harmful soluble salts.
Looking at different traditional materials and compositions, this research aims to design and test a repair pointing mortar able to mitigate driving rain-induced moisture problems in historic buildings. This three-year project, in collaboration with practitioners from Historic England and the Churches Conservation Trust, combines laboratory experiments and test wall trials simulating driving-rain and natural evaporation, focusing on the South-West (SW) of England climatic environment.
In the first phase of the research, wood ash from a biomass boiler, a traditional hydroscopic material, was added in different concentrations (0%, 10%, 20%, 30%, 40%, 70%) as replacement of the aggregate by volume, in mixes using air lime putty and natural-hydraulic lime (NHL, 3.5 St Astier). Evaluation of water absorption by capillarity coefficient (WACC) (BS-EN 1925-2000), vapour permeability (BS-EN 1025-19-1999) and open porosity (BS-EN 1936-2006) were performed. It has determined that wood ash generally increases the open porosity and vapour permeability of lime mortars and from 20% added in a mix, slows down the WACC and the carbonation.
In the second phase, mixes were designed to evaluate the difference between siliceous and calcareous aggregates and binder rich mixes in the formation of the pore size and water absorption and drying property. Samples were exposed to wet curing conditions, similar in average to inland SW England in Summer: 15°C, 85% RH, and compared to laboratory curing conditions: 20°C, 40% RH. Selected mixes from both phases and using quicklime slaked with NHL were applied on granite test walls trials simulating driving-rain in SW England to determine whether the mortar joints help mitigate the ingress of rainfall.
Testing these mixes will improve the scientific understanding of the behaviour of the materials to inform the future design of repair mortars for damp buildings. It will also ensure that repair interventions, conducted by experienced masons using best practice methods, contribute to a sustainable preservation of historic masonry at risk.

Learning Objectives:

Lucie Fusade

PhD Student
University of Oxford, School of Geography and the Environment

Lucie is a doctoral student at the University of Oxford, and part of the UK Centre for Doctoral Training in Science and Engineering in Arts, Heritage and Archaeology (SEAHA). From studying Art and Architectural History at the Ecole du Louvre, Paris, Lucie became interested in the conservation of built heritage at risk, completing an MA in Heritage Management at Newcastle University, UK, in 2012. This interest took her to New Orleans where she researched the recovery of built heritage after Katrina and to undertake work with ICOM in Paris and ICCROM in Rome with the disaster recovery team. She then transitioned into scientific research in built heritage conservation through earning an MRes in Heritage Science (SEAHA) at University College London in 2015. Her current work at the University of Oxford focuses on the design and evaluation of lime based mortars for highly exposed buildings in England in collaboration with Historic England and the Churches Conservation Trust. She aims to continue research linking science and practice, contributing to inform the conservation and management of historic buildings.


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David Edgar

David Edgar is a British conservator, stone carver and restoration stonemason with 15 years experience working on heritage buildings and monuments - most recently the West Block Rehabilitation Project at Parliament Hill, Ottawa.
David has lectured for the Ontario Association of Architects, The Canadian Association for Conservation and the APT, as well as the Universities
of Carleton and McGill. David has recently started his own company, based near Ottawa: David Edgar Conservation Ltd.


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Designing and evaluating repointing mortar mixes for highly exposed and damp historic buildings (church towers) in South-West England

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