Diagramas de interacción

Opposite page Glastonbury. The 12th century north portal of Glastonbury Abbey, UK, illustrates the survival of important sculptural detail in the context of a ruin and the par-ticular care that is needed in recording, condition monitoring, and carrying out periodic treatment. The orders of the portal still have evidence of polychrome. Soluble salts (mainly chlorides and nitrates), are present in the joints, and there are fissured gypsum crusts on much of the detail. Periodic poulticing and reversible lime mortar repairs and crack fillings form the principal mainte-nance interventions.

fixed in their places and settlements stopped. Where the coping stones remain in situ they should be firmly secured, and when they are destroyed, as is generally the case, the upper stones should be set in their places where they are found and means taken to prevent water resting on

the top of the wall and soaking into it. Wherever large apertures exist or where wrought masonry such as win-dow heads etc. have fallen out, they may be restored to prevent further dilapidation, but, in general, it is not desirable to make any restoration of work which is 84 Conservation of Ruins

Figure 4.1 The west front of Tintern Abbey c. 1860. This view is typical of the ‘romantic ruin’ which caught the imagination of Wordsworth and other poets. The heavy ivy mantles conceal the potentially disastrous development of several major structural prob-lems, including the collapse of the south wall of the nave.

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merely decayed and not likely soon to become loose, fall out or otherwise injure the rest of the fabric.

One hundred and fifty years later, English Heritage still seek to follow the same guidelines.

But the pioneering work of the Office of Works was often the subject of considerable criticism and acrimony. Entrenched romantics, defenders of the

‘ivy-mantled tower’, resented the heavy hand of offi-cialdom and, at least in some cases, believed that architects and stonemasons of the right calibre could devise solutions and produce results in a far more traditional and sympathetic way than an Office of Works engineer. Much of the opposition to the work being carried out at some of the first sites such as Tintern Abbey was based on a confidence bred of sound training and experience in the repair of trad-itional buildings. But the Office of Works’ innovative use of concrete and steel to ‘preserve as found’ was, in many cases, the only way to retain broken struc-tures in perilous conditions, and history has largely vindicated the action of its pioneer architects, engin-eers and masons. There is little doubt that without their ingenuity much of what survives today would have been lost; moreover, their achievements were remarkable in being largely undetectable on com-pletion. Where criticism can sometimes be justly made is in matters of detail, and then only with the benefit of hindsight. We know, now, that masonry is not well served by deep-tamping and grouting in cement-based material and that concrete poured against the tails of ancient stones can create stress and damage to the fabric it was intended to save. In truth it can be said, however, that we have learnt more from the experience of the old Office of Works than they might have learned from us, three-quarters of a century later.

A study of the conservation of the Cistercian Abbey at Tintern, one of the earliest sites to benefit from major ‘secret’ structural intervention, is informative and illuminating of the determination of a fledgling government body to implement a philosophy of preservation without restoration, and of the ingenu-ity and imagination of the engineers and architects of the time.

Tintern Abbey is picturesquely set in the wooded Wye valley of South Wales, built over a period of some 50 years, commencing in 1269. Following dis-solution in 1535 it was, as was usual, stripped of its lead roof covering shortly afterwards, thus beginning the slow process of decay and eventual collapse of its roof, vault and tower, and the mantling of its walls in ivy. The romantic appeal of Tintern was much

enhanced by artists and writers of the eighteenth and nineteenth centuries, and it was this legacy which seemed, to critics of the Office of Works (and there were many) in the early twentieth century, to be so needlessly and carelessly degraded.

William Woodward wrote to the Daily Express in July 1921:

It is acknowledged that Tintern was the loveliest of our ruined abbeys, and so it is upon this particular ruin that the Office of Works has bestowed its benign influence.

It has not been satisfied by the unnecessary stripping the walls of their ivy and wild roses, but it has intro-duced its favourite steel and concrete work as if it were complying with a London County Council Dangerous Structures Act.

But the ivy canopies were not only concealing but contributing to the further demise of the ruined buildings. Frank Baines was very positive on the subject and is famously quoted as saying:

There is no more pernicious weed in the country than ivy.

I once used to go about with a small saw, and whenever I saw ivy I cut its throat.³

One of the first structural analysts of the substantial ruins of Tintern at the time of the First World War was William Harvey, whose studies of Tintern, Rievaulx, Westminster and St Paul’s Cathedral were published by the Architectural Press in 1925,⁴ advo-cating the essential practice of knowing the whole building to understand its movements and the rea-son for distortion and fracturing. Two major areas of concern were identified at Tintern, once the ivy was removed. The first was a progressive westward movement of the north chancel wall, towards the great arch of the missing tower and the overhanging broken end of the north arcade of the nave (Figure 4.2). Local repairs were not able to contain this westwards movement, as the north-west pier distorted and developed a pattern of fine stress cracks. The drift of its masonry piers in the chancel to the west could only be restrained by the installation of the reinforced wall head beams shown in Figure 4.3. The corbelled masonry of the nave arcade could only be supported by the installation of the steel ledgers shown in Figure 4.4b.

The second major potential collapse was of the south wall of the nave. There it was found that the head of the wall, at its centre point, had a lean to the north of just over half a metre. The instability of the wall was confirmed by cracking patterns. Two options to correct the problem were considered:

either to replace temporary timber shoring on the

north side erected by the Office of Works, with masonry buttresses, or to devise a method of tying back the head of the walls. This second option was selected both for reasons of avoiding visual intrusion in the nave and through fears of possible settlement of massive buttresses which would exacerbate the problem.

The proposal to tie back the wall head was made distinctly more feasible by the presence of a south aisle which once had a single pitch roof. Replacement of this roof, whose line was clearly evident at east and west, would enable a system of reinforcement to be introduced. A lattice girder was installed to restrain the nave walls and bolted through the nave wall with-out attempting to correct the distortion. The lattice girder was finally covered with oak rafters and tile-stones, leaving the soffit exposed. A secondary oper-ation involved the substituting of the heavy timber shores with brick masonry supports to enable the shattered masonry of some of the piers to be strengthened by cutting out and inserting steel stan-chions within the core of the nave piers; the steel was subsequently concealed by replacing original stones, or new stones where the originals had been shat-tered, and the brick supports removed.

These were the engineering works that so enraged William Woodward and others in the 1920s, but illus-trate the ingenuity and care which were taken to

transform a dangerous structure into a stable ruin. A certain pride developed based on the ability of archi-tects, engineers and masons to execute major and minor works that were subsequently not easily detectable. Other major sites that received early structural attention and general masonry consolida-tion were the abbeys of Jedburgh, Furness, Rievaulx, Whitby, Byland and Netley, and the castles of Caernarvon, Kirkby Muxloe and Goodrich. It was on such illustrious sites as these that the ‘Ancient Monuments’ team of professionals and craftsmen cut their teeth and developed considerable expertise.

Undoubtedly there was, and remained, a critical benefit in accumulative experience of the group and its continuity between and after the two world wars.

While adverse criticism may be levelled, sometimes justly, against directly employed specialist works teams, there is little doubt that they have a distinct advantage over contractors in becoming familiar with their historic sites over many years and in knowing the techniques and standards required. In the absence of any such in-house team of expertise, the provision of adequate specialist training for architects, survey-ors, archaeologists, engineers and craft technicians becomes even more important. This subject is addressed in Chapter 8. Based on review and study of the many pioneering works in monument con-solidation, which were practical interpretations of 86 Conservation of Ruins

Figure 4.2 William Harvey’s drawing of the north chancel wall showing the drift of the masonry to the west.

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Figure 4.3a William Harvey’s elevation and plan showing the proposed installation of reinforced concrete wall head beam linked to a ring beam at the head of the tower.

Figure 4.3b Reinforcement of the corbelled masonry of the broken nave arcade.

conservation philosophy and which, at a major structural level, are illustrated in Figures 4.2 – 4.4, certain disciplines and methods have been developed in the approach to the ruin sites which can now be described.

Context and definitions

The most often repeated phrase in historic fabric conservation must be ‘conserve as found with min-imum intervention’.

‘Conserving as found’ is, of course, a philosophy whose implementation is governed, at least in part, by the nature and condition of the site, but it should influence every decision and remain as the ideal goal.

In particular, essential conserving works should never introduce speculative restoration, or damage or alter evidence of the original buildings, or conceal the cause and character of their past deterioration and collapse.

‘Minimum intervention’ is the other familiar guiding principle for conservators of ruins, as for conservation of more complete historic buildings.

Unfortunately, fundamental as the principle is, ‘min-imum intervention’ cannot always mean doing very little, and a virtue should not be made of it where more serious intervention is actually needed. Largely worthless, low-key interventions are really only placebos, and may be illustrated by, for instance, the tamping and pointing of fractures without analysing the cause of fracturing, or installing an anchor within a crack or a bulging wall when what is needed is a programme of recording, taking down and rebuild-ing ‘as found’.

Difficulties arise in two common ways. The first may be illustrated by a scholarly, theoretical demand that everything should be ‘conserved as found, with minimum intervention’, which is partly or largely ignorant of the materials or construction and the dynamics of an impending collapse. The second may 88 Conservation of Ruins

Figure 4.4a Tintern Abbey - North west pier showing timber shoring under broken nave arcade. This overhanging masonry was repaired in the manner shown in Figure 4.4b.

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be illustrated by an ignorance of any real belief in conservation principles, coupled with preconceived ideas of how standard building repair solutions will resolve the problem. The combination of both atti-tudes, which again is not uncommon, is inevitably damaging for the site where they meet.

Research into, and monitoring of, conditions found on ruin sites are often desirable and are sometimes essential. The benefit of a multi-disciplined team with continuity of experience is that information is collec-tive and the risk of unnecessary duplication is avoided;

but the individuality of ruin sites is such that there is always likely to be an element of investigation and treatment trial, most commonly in the design of mor-tars and often in the monitoring of fractures.

Structural archaeology

The informed, visual examination of any structure, but particularly an historic ruin, will usually enable some, and perhaps a great deal, of its building his-tory to be deduced. This kind of examination was described by the late Patrick Faulkner as ‘structural archaeology’.⁵The process is multi-disciplinary, and in the first stages architect, surveyor, engineer, archae-ologist, historian and materials scientist may all be involved. In the later stages the ‘conservation tech-nicians’, those who must unpick, clean, consolidate and stabilise, are always also involved; in fact, they are often the first to see anything not immediately exposed on the surfaces. This is one of the many reasons why their role is so important and so demand-ing of traindemand-ing. They are in a position both to reveal and illuminate or to destroy.

Structural archaeology is quite distinct from tural analysis, which is based on a study of the struc-tural content and condition as described in Chapter 2;

its evidence is final and incontrovertible, overriding even archival record. Typical features occurring and to be looked for in the ruined structure may be listed as follows:

● Shadow lines indicative of the removal or decay of a feature

● Surface cavities such as putlog holes or lost fixings

● Assembly marks

● Changes in wall thickness

● Changes in construction type

● Changes in materials.

The last category may be immediately obvious but more often is rather subtle in character, especially in the case of mortar or plaster. Long exposure to, and experience of, the materials can become very important if evidence is not to be unwittingly destroyed. In some countries, especially, for instance, those which formed part of the Roman empire, mor-tar (used as lumps of aggregate), stone, brick and tile were extensively salvaged and reused. Areas of salvaged material may crop up randomly in post-Roman con-struction, indicative of periods of demolition and spasmodic delivery, and some may be recycled more than once.⁶ Accurate survey plotting of properly identified materials is an important aspect of struc-tural archaeology.

Temporary supports and protection A condition survey, or even a more basic, prelimin-ary survey, will identify parts of a building and its site which are at risk and which may present imme-diate dangers. In this category might be, for instance, seriously leaning walls, new or spreading fractures, bulging facework with open joints, displaced stones at high level or major landslips. Conditions of this kind often require immediate intervention both to support, contain and protect the ruin from further loss, and to protect visitors, legitimate or not, from injury and possible loss of life. Work of this kind will also be required on sites in poor condition which are unlikely to be consolidated and conserved for many years, and, within the context of a current con-servation programme, areas which could be lost or cause injury to contract personnel.

In order to design and place such support and pro-tective temporary structures, a thorough understand-ing of such ruined buildunderstand-ings and their condition is essential. A heavy-handed and ignorant approach could cause collapse of large areas of masonry and possible loss of life of those carrying out the works.

Typical temporary support and protection works are illustrated in Figures 4.5 – 4.9.

On some sites, removal of vegetation is required in order to inspect the masonry and make some assess-ment of its condition. This operation requires more care and understanding than is generally appreciated, and should in any case be preceded by consideration of the ecological impact removal will entail (see Chapter 6).

Figure 4.5 Installation of temporary timber supports in the form of plates, props and wedges and synthetic rope net over vegeta-tion and loose wall head, weighted with sand bags.

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Figure 4.6 Small lancet window largely unconnected to its original masonry has been provided with corset plates bolted through the open-ing to provide temporary stability.

Figure 4.7 Leaning and fractured wall provided with simple temporary buttressing of concrete blocks, and ringed with security fencing. Myross Church, Ireland.

92 Conservation of Ruins

Figure 4.8 Temporary support of high leaning wall in the form of board facings and flying shores.

Figure 4.9 Temporary protection and insulation of masonry against rain and frost and temporary support works, County Cork, Ireland.

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Removal of the foliage and thin, easily accessible stems with shears can usually enable a condition assess-ment to be made of the masonry without trying to move heavy growth. Well-developed plants such as mature ivy (Hedera helix) are often found to be clasp-ing and supportclasp-ing unstable areas of masonry, so that premature or injudicious removal can result in local collapse and injury. Where trees have established themselves in the masonry, the usual approach is to cut them back to within 600 mm of the building face; however, consideration must always be given to effects that the release of the applied loading may have on the wall as the weight of the tree is removed.

To avoid local collapses it may be necessary to install some temporary support to vulnerable areas before trees are cut.

A common practice in removing ivy is to cut out a metre section of the plant close to the ground to allow the plant to die on the wall and to poison the root by forming a frill girdle and applying a paste of ammonium sulphamate. There is no reason why this practice should not be followed unless a long period of time is going to elapse before clearance and con-solidation of the wall can take place. If there are considerable delays, the dying plant may no longer be able to support unstable, overhanging masonry and may penetrate the structure at higher level in order to seek out the nutrients it has been denied at ground level, leading to further disruption, displacement and stress within the wall. In these situations the plant should not be cut at ground level until a work pro-gramme can proceed.

Wall tops (Figure 4.10)

Where walls still stand to their original height, the exposed and untouched wall tops of a ruin are often

Where walls still stand to their original height, the exposed and untouched wall tops of a ruin are often