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Building Stone Decay And Lime Mortar Compatibility - A Review

Part 1 Dissertation 2001
Rex Harries
Cardiff University Cardiff UK
This dissertation has arisen as a consequence of working with stone and lime-mortar at the Royal William Yard, Plymouth. It is primarily concerned with building stone decay and lime-mortar analysis and compatibility.

The review of stone conservation summarises the philosophy proposed by SPAB, English Heritage and International Organisations and outlines the current approach. The review of stone decay acknowledges the complexity of the underlying process that involves interactions between stone, its location, the landscape and the environment. These complexities are not unravelled by durability tests and exposure trials. Research has been focused almost exclsively on the younge r'Portland' type limestones and has ignored the oder limestones typical of the case study area.

The literature review on lime-mortar traces its rise and fall in popularity and hints at a current revival. This has been accompanied by a renewed interest in its analysis, both by simple and sophisticated techniques. Analysis is seen as the most effective way of matching old and new mortars. However, complexities of identification associated with the 'reaction product' of pozzolans and hydraulic limes has ledt unresolved the issue of methodology.

The case study at the Royal William Yard develops a methodology which explains the underlying process of stone decay. This has been achieved through on-site visual analysis, microscopic examination and structural analysis. The diffuse boundaries between stone replacement, stone repair and non-intervention are resolved with reference to aspects of safety, structural stability, depth and extent of decay, damage due to human activities and a projected life-span estimate of less than -100 years.

Lime-mortar analysis in the case study has focused on the simpler techniques of on-site visual analysis and microscopic examination to match old and new mortar. This has been effective in characterising the aggregate and in determining the binder:aggregate ratio. Compatibility in terms of performance is more difficult to evalute in the absence of acceptable specification criteria.

A comparative evaluation of the approaches adopted in the literature and in the case study informs my personal perspective of 'best practice' as applied to the conservation of stone and mortar.

Rex Harries

Rex Harries dissertation is exceptional in my experience both in the extraordinary amount of work that went into its preparation and the high standard of the result. it is an in-depth analysis of the differences between the approaches to stone decay, stone conservation and lime-mortar analysis set out in current and past literature and the approaches which are practicable and effective for use on site. The literature review and analysis is detailed, exact and thorough. The case study, which is based on personal experience of working on stone conservation at the Royal William Yard, Plymouth, is carefully reported and gives useful insights into the on site application of recommended techniques.

This mature student, who cares passionalely about his area of expertise, has follewed an unusual career path which has given him expert knowledge in the properties of stone and lime mortar. His external examiner felt the dissertation to be of an extrememy high standard, to be publishable 'as it stood', and to make an original contribution to the current body of knowledge in this field

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