Science and Heritage Programme
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Weathering and decay in historic magnesian limestone: Application of X-ray techniques to inform cathedral conservation in the 21st century

University of Cardiff/ York Minster

Award holder - Dr Karen Wilson
Student - Rachel Walker

PROJECT SUMMARY

Magnesian limestone is one of the most important building stones used in the construction of historical architectures in UK, Europe and North America. However, the sheer diversity of the stone has created problems with selection of replacement material, construction methods and conservation protocols. To date there has been little systematic or scientific study of the chemical composition and the weathering and decay mechanisms which result from the distinctive character of this stone. Decay mechanisms may be affected by changes in atmospheric pollution, climate change, or complex micro-climates that may exist in for example exposed or sheltered regions of a building.

This project takes advantage of a unique opportunity to explore these issues, namely the scaffolding and proposed restoration of the East End of York Minster. Cutting edge X-ray techniques will be applied to characterise the chemical composition and structure of materials (both building stone and mortars). This information will be used to explore the mechanism of weathering and decay to guide the use of conservation techniques and materials in future restoration of York Minster and other historical buildings.

RESEARCH OBJECTIVES

  • To apply X-ray based analytical techniques to determine the structure, composition and effect of impurities (e.g. Mg, Fe) on magnesian limestone weathering.
  • To identify how micro-climate affects weathering mechanisms.
  • To examine the effect of protective coatings on weathering and decay.

THE MOST IMPORTANT RESEARCH QUESTION

To understand the weathering and decay mechanisms experienced by historic magnesian limestone masonry (including ashlar and sculpted stone).

RESEARCH METHODOLOGY

To use a range of X-ray based techniques to characterise Magnesian limestone and mortars to understand the mechanism of erosion when exposed to atmospheric pollutants.

EXPECTED OUTCOMES

Year 1: Study the reaction of SO42- with dolomite and identify the role of impurities.
Year 2: Study the curing of mortars and recrystallisation during mortar weathering.
Year 3: Study mortar erosion by organic acids to assess the effect of modern pollutants.

SOCIAL, ECONOMIC AND ENVIRONMENTAL IMPACTS

In common with historic structures of this age York Minster has suffered extensive aging of both stone and glass, largely as a result of atmospheric pollution. Greater knowledge of the behaviour of lime-based mortars under the aggressive 21st century chemical environments prevalent in modern towns and cities is therefore essential to guide future conservation.

RESEARCH SUPERVISORS

Dr Karen Wilson, Dr Adam Lee (University of Cardiff) and Dr Kate Giles (University of York) in collaboration with York Minster.

ABOUT RACHEL WALKER

Rachel Walker

Rachel Walker is 29 years old, and was born and raised in Caerphilly, South Wales, where she currently lives with her 2 young daughters, Jennifer and Sophie, and their pet cats. She graduated from the University of Glamorgan in 2009 with a BSc in Forensic Science.

Rachel joined Cardiff University in October 2009, and is currently working on her PhD which focuses on the use of x-ray and spectroscopic techniques to gain a better understanding of the weathering and decay mechanisms of magnesian limestone, a popular building material employed throughout Europe and the USA for the construction repair and restoration of historic monuments. The project is in collaboration with York Minster, the largest Gothic cathedral in northern Europe, which has occupied the same site since 600 A.D.

Predominantly built from magnesian limestone, the Minster has undergone extensive reconstruction and renovation cycles over the past millennium due to the damage caused to masonry (both mortar and stone) as a result of atmospheric pollution and weathering, and also restoration treatments previously used. 

Samples of authentic stone from York Minster have been analysed via XRD, SEM and DRIFTS. These techniques have provided information in relation to the chemical composition and the morphological structure present within the samples. It has also been possible to quantify the minerals present. The next stage of the project will be to monitor the rate of the reaction when the samples are subjected to sulphation, to mimic the natural acid rain process in the atmosphere, which exposed such stone to sulphuric acid. 

By gaining a better understanding of the chemical composition of the stone, different stones which have been used over different time periods, and of the weathering and decay mechanism of magnesium limestone, it is hoped that preventative measures can be employed to potentially alleviate/delay the decay process.


LINKS AND CONTACT DETAILS

York Minster
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