Stone Restoration Handbook E-Book

Chris Daniels

• Herausgeber: Crowood
• Kategorie: Fachliteratur
• Sprache: Englisch

Veröffentlichungsjahr: 2015

Beschreibung

Whether you are an artisan, an architect or a homeowner, The Stone Restoration Handbook demonstrates the best approach and techniques to use when preserving and repairing historic buildings. It introduces the materials and the processes, and explains the proven methods to conserve, repair and restore stone, masonry, statuary and monuments. This new book is packed with illustrations, examples and advice on stone selection and working, lime and mortars, pointing, cleaning and repairing mortar and stone. It guides you through assessing the job on the first site visit through to discussing the options and difficulties you can face. This is essential reading for those who care for and repair historic buildings and monuments. Contents include: surveying for a conservation report; setting up workshop and tools; stone selection and working; lime and mortars; pointing; repairing mortar and stone; cleaning; consolidation; casting and scagliola. Superbly illustrated with 564 colour photographs.

Leseprobe

THE

STONE RESTORATION

HANDBOOK

A practical guide to the conservation repair of stone and masonry

CHRIS DANIELS

First published in 2015 byThe Crowood Press LtdRamsbury, MarlboroughWiltshire SN8 2HR

www.crowood.com

This e-book published 2015

© Chris Daniels 2015

All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopy, recording, or any information storage and retrieval system, without permission in writing from the publishers.

British Library Cataloguing-in-Publication Data

A catalogue record for this book is available from the British Library.

ISBN 978 1 84797 908 7

Acknowledgements

Thanks for help and support are given to Blossom, Lily, Rudi and Cadhla; Antony ‘Hank’ Denman; Richard Mortimer, David Good and students at Weymouth College; Ian Constantinides; Niall Finneran; Andrew Whittle, Ian Burgess and all other colleagues and past students.

CONTENTS

Introduction

1 Decay of Stone

2 Producing a Report and Selecting the Stone

3 The Workplace

4 Tool Skills

5 Limes and Mortars

6 Repointing

7 Dutchman Repairs

8 Mortar Repairs

9 Consolidation of Stone

10 Cleaning Stone

11 Casting

Appendix 1: Putting in a Slab

Appendix 2: Keeping it Together

Glossary

Index

Exeter Cathedral, Devon. Built in 1153, this is a major Gothic cathedral that, like most buildings of this style and period, needs consistent maintenance and repair. This is where the skills of the conservator and stonemason become one.

INTRODUCTION

Therefore when we build, let us think that we build for ever. Let it not be for present delight, nor for present use alone. Let it be such work as our descendants will thank us for, and let us think, as we lay stone on stone, that the time is to come when those stones will be held sacred because our hands have touched them, and that men will say as they look upon the labour and wrought substance of them, ‘See! This our fathers did for us.’ (John Ruskin)

Welcome. This is a book intended to give an introduction to the practical processes for the repair and conservation of stonework, covering techniques and application in the workshop and on site; it will also be useful to those involved in the commissioning and administrating work of this nature. ‘Artisan’ will be the term used for the person this book concerns itself with; my demand of you, the reader, is that you have an enquiring mind, an ability to learn and are willing to explore. The thread running through all the chapters will be the encouragement to enjoy and appreciate this work and objectives, in all their qualities and uniqueness. Complementing this will be an emphasis on the correct attitude to this work; the successful preservation of our built heritage is a task of such significance that, if you are not the masonry equivalent of a tree-hugger, then it may not be the career for you. Good luck with whatever you wish to do, or, better still, read this book, get excited, get involved, and perhaps join our ranks.

This replacement bracket in Bathstone involves a combination of topics covered in this book: bad practice – the building had been covered with a stone sealer to prevent damp, subsequently making the problem worse; decay – where the trapped salts have destroyed the stone and fabric as well as allowing moisture to be held in the fabric; stonemasonry -needed to work the replacement to match the original; fixing skill – to put it in; lime – for the mortar work and grouting of the core; and casting – copies were made in cast lime to put in as sacrificial units that would draw out the moisture.

The Essential Human Toolkit

We are all imbued with basically the same learning facilities and have evolved brains that can control our hands to perform wondrous feats far beyond the requirements of rudimentary DIY. If you want to do something badly enough, you can acquire the skills to do it. So the first thing to be pulled out of the ‘toolkit’ is attitude. With a positive attitude, the work, no matter how insignificant, becomes part of your life. To be able to do things that enhance, prolong and beautify the environment we live in is profoundly human and leads on to the next attribute – pride. We are not talking about sin here, rather the warm satisfaction in looking at what you have done, feeling that it was the best work you could produce and reckoning that it has been done correctly.

New bottom half of a heraldic shield, pieced in to replace the decayed section. Although the original was wholly made from the same stone at the same time, it shows that there can be extremes of performance from what would, technically, be described as the same material. (Photo: Harry Jonas)

For those new to the use of tools, there will be the basic outlines for handling and using them. Rest assured that it is relatively easy and yet pleasantly satisfying to be dexterous in the use of your equipment. Just take care, practise in safety and if in doubt ask; most artisans are happy to help in the acquisition of skills by interested people, so knock on workshop doors and engage in conversation on site.

Added Interest

Throughout this book are photographs drawn from a variety of projects, many included to add another aspect beyond just the topic of the text. I hope they will begin to illustrate for you some of the range that can be found in work like this. Where there is little to illustrate in the text, interesting pictures will be shown that have some connection with what is being talked about. They will also demonstrate that many of the topics in the chapters are interrelated; in this work it is important to take a holistic view of issues and realize they cannot be categorized simply as having one thread. I have been practising this work for almost three decades now and have not had a single job that has not introduced new aspects, required novel solutions or needed the ability to adapt the technologies available.

The route to successful practice in this area of conservation work is not easily defined, for it is a mélange of many studies: architecture, art, history, science, technology and research, coupled with practical skills that, personally, range from welding and metal fabrication, through stonemasonry, sculpting, carpentry (not joinery though!), brickwork, plastering and mould making, to engineering and mechanics. Though this array may seem formidable, it is well within the grasp of most intelligent adults who find learning enjoyable and have the correct attitude for acquisition of new talents.

It would be nice to be able to decide on a proper definition for the work covered here, or for any practical work to the built heritage, and for ease it is termed ‘conservation’; this term can be interpreted in many different ways, such as restoration, repair, renovation, maintenance, amongst others. The bottom line is that work carried out is appropriate to the needs of the building and its preservation; how much and to what, is up to those involved.

Sometimes complicated issues can be resolved with experience and common sense; the cleaning of delicate marble statues, rather than raising it to complex levels of chemicals and poultice, often just involves a bit of time and some warm water.

Checklist

In the majority of this work the aim is to preserve and protect the historic fabric fittingly, using the least aggressive techniques and minimizing the amount of new materials used; hence our most used term, ‘minimum intervention’. Obviously, interpretation of levels of intervention deemed necessary for use in conserving historic buildings can vary widely; definitions become open to reason when taking the following topics into consideration:

•   Original material used in construction should, if possible, be preserved as is, without moving, adding to or covering up with new material. Obviously, some change will be wrought on a building; necessary alteration/repairs (as will have happened in the past) are often to be considered part of the history.

•   History is the visual and physical record of what has happened to the building and should be preserved as diligently as the original fabric. When the changes have been dramatic for change of use or expansion then this can have repercussions on the aesthetics.

•   Aesthetics cover how a building looks, which is as important as how it is constructed, so work that is necessary for the preservation of the fabric should be appropriate in finish, and should not disrupt the design of the building or its detail by imposing suppositions and modern material finishes inappropriately.

One of my first jobs as a conservation stonemason was to build a protective layer on this fallen chunk of masonry in Corfe Castle; it was to consolidate the exposed crumbling rubble infill in such a style as to still tell the story of what had happened by showing lines of rubble as they would have been during building. The use of flint has been suspended for some time for this work since then, as the realistic look was replaced with a safer, more anodyne ‘rockery’ style.

Slightly false historic evidence of a cannon ball lodged in a wall lends interest to a building. The problem for us is how this should be treated.

Wrought iron armature dating to the nineteenth century, used to support a medieval vault; this was subsequently replaced with a stainless steel frame to do the same job. Wrought iron is incredibly resistant to rusting; it was only the later ferrous fixings that had caused the problems.

•   This work, if possible, should have a factor of reversibility. Our work should allow future historians and conservators, if necessary, to remove the modern interventions to get back to the original material, perhaps to carry out research or use more up-to-date repair techniques. Reversibility is often pushed down the table of desirable properties, especially if it affects the practicality.

•   Practicality: this is paramount to getting the job done effectively using techniques appropriate to the task -cleaning large areas of masonry with cotton buds and litre bottles of de-ionized water is not practical! Thus a major factor here is common sense. The extent of the work, the use of specialist techniques and the level of intervention will rely often on the funding.

•   Funding: clients are all too often given an indication of what a project will cost which, due to imprecise specifications written by non-practitioners, runs over budget; conservation specifications should be written by conservation professionals or specialist contractors to get the most pertinent deal, and these should deal with the building’s needs.

•   Vulnerability and needs: these aspects can come under threat so it is up to those with practical experience and skills to recognize the full extent of these criteria, how they can be worked with and how the repair work can be maintained.

•   Maintenance: aside from necessary repair, the permanence of our built heritage relies on someone looking after it, so a schedule of required care should be drawn up for the structure and any intervention must fit into this programme; this should be viable in terms of practicality and economy to ensure it happens.

Salisbury Cathedral, like most buildings of this type, has permanent staff continuously repairing, replacing, renewing and caring for the fabric. Their work will never be finished, due to the small number of people involved, the size of the building and, most pertinently, the cost.

Chemical cleaning trials in Wakefield Cathedral undertaken as part of the investigation as how to revamp the interior. This work was carried out prior to our engagement and unfortunately the records were vague and did not help in anyway; pressurized steam was our preferred method, which came up with comparable results that are more practical and kinder to the stone.

CHANGING TIMES

It is important to note that though the majority of conservation is carried out with the best of intentions, the use of seemingly correct materials in the wrong manner and application can not only be harmful but hasten decay. Conservation and restoration is an ever-evolving subject, and what may have been seen at a particular time as a suitable treatment, material or process may be acknowledged with hindsight, in some cases, to be detrimental. This may also come to be the view on methods in vogue today; while understanding of the factors involved in decay and how materials alters over time appears to be a much more precise science, there is still much mystery as to the precise nature and activity of many forms of decay.

Dichotomy

As there are policies (such as the Venice Charter) that adhere to the principle of producing work that should be readily identifiable as a modern intervention, it may be acceptable to use a stone or repair technique that may seem visually different, as long as it is physically compatible or its performance is supportive to the original material. This ‘honest repair’ is often evident in museum exhibits where it does not detract from the original piece, highlighting the found condition by not being afraid to show the extent of new work. John Ruskin was generally opposed to restoration that was hidden, in 1849 calling it ‘… a lie from beginning to end’. His opinion was that remedial work should be seen: ‘Do not care about the unsightliness of the aid, better a crutch than a lost limb.’

We are all in this game for the good of the structure while simultaneously preserving our heritage. While work should be harmonious and complement the existing, we must appreciate that function begets form, rather than the other way round, the accepted approach demanded by many organizations involved in heritage preservation. Clients (generally those not in the field but paying for the work) are more inclined to invisible restoration, where the work carried out blends in to the original, presenting the patinated appearance of an untouched building, occasionally leading to renewal; these two approaches are often a cause of contention, and probably will always be so. This book is not overly concerned with the specific theoretical reasons for doing the work, or what is to be used for possible situations; all those issues are for the artisan and the other players to hammer out. Here, the wish is to give some idea of how to do it, and what kit is needed, though my opinions will occasionally surface, and helpful asides will add to the pot.

Mutual Understanding

The preponderance of educated people with few or no practical skills is an issue that affects all walks of life, but here we must concentrate on our world. There is a substantial chasm between those that pay for or need craftspeople’s work and the actual craft workers themselves; the former may well feel detached from the structures for which they are responsible, and the latter may often be too busy actually getting on with the work to spend time carrying out the necessary social milling. This will always be an issue; and overall the downside is a glut of experts and facilitators who contrive to organize, manage and inspect the work to our built heritage without real attachment. The society in which we find ourselves creates a system where people do not appreciate the experience and skills of the artisan, considering that to do manual tasks indicates a lack of intelligence and wit, and many artisans feel that with no practical skills these people lack the same, so there is a barrier between these two factions that has caused some ridiculous errors or wastes of time. This does not mean that all is lost. There are many people on both sides of the fence who respect the other’s contributions; when this occurs the result is outstanding and worthwhile. The future of our profession should be full of cooperation and respect.

The mortar design bench, for on-site production of a matched repair mix. Much of this work involves improvisation and adaption of methods to deal with singular issues; recipes will not be doled out in these pages as it could be dangerous to bring preconceptions to the project – they are all going to need their own tailor-made mixes.

The Society for the Protection of Ancient Buildings (SPAB) was one of the founding bodies that concerned itself with conservation rather than restoration. In 1877 its founder William Morris wrote in the manifesto:

It is for all these buildings, therefore, of all times and styles, that we plead, and call upon those who have to deal with them, to put Protection in the place of Restoration, to stave off decay by daily care … to treat our ancient buildings as monuments of bygone art, created by bygone manners, that modern art cannot meddle with without destroying.

Sound words up to a point, that point being the last bit, where he underlines the reason why many academics and critics do not trust practitioners to do the right thing; the implication is that it is better they are not encouraged to do so in their mundane manner. We must set this to rights and prove him wrong.

During this conversion of a great house to a hotel, advice on behalf of statutory bodies was that all the mortar repairs be ‘eroded’ rather than follow the existing lines, as they wanted to show the eroded and interesting history of the building. This desire to produce a faux appearance of ‘artistic’ wear and tear can be a thorny issue between the artisan (who wishes to respectthe building with work that states the quality of the hand) and the white-collar specialists who, in fear of being blamed for too strong an intervention, opt to reduce the result to a safe level that they can argue for. Happily this cowardly approach was successfully argued against and the sharp Victorian masonry was skilfully bought back to life.

A rainy day in Bath. The façade of this shop is soiled by scurf, the result of acid rain pollution and accumulation of sooty particulates. The impervious painted sign is causing water to run off and keeping the stone clean directly below it by washing, while under the cornice the scurf builds up.

CHAPTER ONE

DECAY OF STONE

The problem with buildings, and the reason for this book, is that over time they will wear out. The process can pass unnoticed until it gets really bad, as buildings are at the mercy of the ravages of time, the elements and, quite often, of people. With such a hardy material as stone it is often an accumulation of factors that will set about the demise of a building, and once started it is very difficult to reverse the process.

Heritage conservation has the responsibility for reducing the impact and, where possible, setting things right – but always without losing the essential character of the structure.

What is the Problem?

The first step is to identify what is happening and what is causing it. A building will tell us what is happening to it; interpreting the story requires an ability to read the signs, plus common sense and intelligence. What will become noticeable in this chapter is that there is one unifying factor: water.

The Inspection

The extent of investigation here is assumed to be an overall view of what is happening to a building; the depth of this study will be defined by what is found. First, make sure you have all the kit needed and try to choose a good day: too much sunlight may mean that significant details may be hidden in shadow (though you will get nice pictures) and, obviously, it should not be too wet.

Roman column, Nîmes, France. Gently wearing away with time, inevitable but true to nature.

THE ROLE OF WATER

It can be generally assumed that where there is decay of stone that is not wholly caused by structural movement, water will be or has been significant to the process. Stone will at some time come into contact with water, or be contaminated by moisture; problems arise when the water carries soluble materials, is blocked in its travel or exerts unwanted pressure. If a stone could be isolated from any form of moisture it would probably remain whole, with no significant degradation taking place. As this situation is one that is impossible to maintain, because buildings are exposed to the elements, it is in the best interests to identify the deteriogens, to render them and their source inert or to remove them. Obviously artefacts such as monuments or statuary can be insulated to a degree from moisture ingress by the use of DPMs underneath or where they touch walls, but this is impossible with buildings.