Architectural Heritage Protection: Guidelines for Planning Authorities

1. Page 121

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   Architectural Heritage Protection Guidelines for Planning Authorities 119 a) identification of the existing stone; b) the specification of any replacement stone; c) a sample of that stone; d) the proposed surface finish of any new ashlar; e) the method of coursing; f ) the specification and extent of any proposed repointing; g) the techniques to be used in carrying out the works, and h) the experience and expertise of the people who will be responsible for the work. Indenting 8.3.7 Indenting is the replacement of an individual decayed stone where that stone has been damaged or decayed to the extent that its structural integrity is in doubt. The term is also used to describe the cutting out and replacement of a decayed part of a stone. 8.3.8 The need to indent all or parts of stones may arise from the existence of iron cramps originally used to fix the stonework. Iron is susceptible to rust and expands on rusting, resulting in the cracking or spalling off of parts of the surrounding stone. Where this has occurred, it may be necessary to take remedial action to remove the cramps, replace them with a non-ferrous cramp and repair the damaged stonework. 8.3.9 Any proposed indenting should be carefully assessed, as indented stones can be visually intrusive. Leaving the damaged original stone may often be a more acceptable option. New indented stones should be finished by hand, where appropriate, to provide a finish which would blend in with the existing stonework while allowing it to be clear on close inspection that this is not the original material. Redressing of stonework 8.3.10 Redressing an ashlar façade involves the removal of the original face of the wall. This can cause considerable damage to the appearance and character of the building with the loss of original tooling patterns, moulded detail and the patina of age. 8.3.11 There may, however, be exceptional circumstances where redressing could be permitted, for example: a) where so many stones are decayed that no other solution is possible; b) where the face of the stones has become badly disfigured by spalling; c) where the deterioration is so severe as to pose a threat to the general public. 8.3.12 Redressing should generally not be permitted, especially where there is carved detailing to the stonework. In many cases where redressing of stonework is proposed, it may be necessary to encourage the applicant to accept the existing appearance of the stonework. Mortar repairs to stonework 8.3.13 Damaged stonework can be repaired using specialised mortars, sometimes known as ‘plastic repair’. Extensive mortar repair work should not normally be permitted unless the façade has already been painted and is likely to continue to be painted. CHAPTER 8 WALLS AND OTHER STRUCTURAL ELEMENTS Where there has been mechanical damage or spalling of a stone, it can be repaired using a small indent, tooled to match the surrounding stone. The indented stone should respect the original joint lines of the wall Iron cramps were traditionally used to hold stones in place. However, iron is susceptible to rusting and, on rusting, expands, often cracking the surrounding stone which spalls off so exposing the iron to further rusting. In severe cases, such as here, it may be necessary to remove the iron cramp and replace it with a non-ferrous metal such as stainless steel or phosphor bronze and repair the damaged stonework The repair of stonework using specialised mortars may be permissible if appropriately specified. However, the long-term effect of weathering and other interventions should inform a decision as to its suitability. In this case the erosion of the face of the stone following grit-blasting has left an old mortar repair standing proud; it will inevitably fail taking more stone with it

2. Page 122

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   CHAPTER 8 WALLS AND OTHER STRUCTURAL ELEMENTS Architectural Heritage Protection Guidelines for Planning Authorities 120 8.3.14 Where mortar repairs are proposed, the work should be carried out by specialists and be appropriate to the fabric and appearance of the original stonework. The applicant should be able to satisfy the planning authority that the specification of the work will not promote further damage of the stonework. For example, the use of hard cement-based mortars will accelerate decay in many cases. The use of large elements of cast stone (sometimes described as ‘reconstituted’ or ‘artificial’ stone) should not generally be permitted as a replacement for original stonework. Cast stone rarely possesses the same visual or performance properties of the surrounding stonework and will look and weather differently. Repointing of Stonework 8.3.15 Repointing has the potential to cause physical damage to the fabric of the building, radically alter its appearance and substantially detract from its character and quality. A proposal to repoint stonework of a protected structure, which would materially alter its character, requires planning permission; and, where permitted, the work should be carried out by experienced people and under the direction of a specialist with a working knowledge and experience of historic buildings. 8.3.16 Repointing should be considered a repair which replaces lost or damaged fabric with that of a compatible and appropriate mix (or series of mixes), material and appearance, providing always that the existing pointing is not inappropriate or damaging to the stonework. Comprehensive repointing of a structure is rarely necessary, unless the existing pointing has deteriorated and is causing damage to the stonework or other fabric. It should be a condition that sound old pointing is left undisturbed as it is an essential part of the fabric and character of a historic building or structure and should not be removed unnecessarily. 8.3.17 Visually, any new pointing should be subservient to the stonework and for this reason obtrusive pointing methods such as ribbon, weatherstruck or strap-pointing should not be permitted unless it is proven that that was the original design intention and not merely a previous unsuitable intervention. Care should be taken to preserve the original pattern of work in cases where the joints contain pinnings (spalls) or galleting. Any pinnings (spalls) dislodged in raking out should be retrieved and reused. 8.3.18 Existing mortar should not be cut out with inappropriate mechanical cutters, such as anglegrinders, as these will inevitably damage the arises of the ashlar, widen the joints and so materially alter the appearance of the stonework. The use of mechanical tools in the hands of specialist conservators may be appropriate for the removal of later cement repointing. Stone cleaning 8.3.19 The cleaning of stonework can materially affect the appearance of a protected structure or the character of an ACA. The potential of stone cleaning to cause irreversible damage means that where works would materially affect the character of such a structure, these works will require planning permission. Unco-ordinated cleaning can create aesthetic problems where a building forms part of a terrace. Where a proposal is made to clean a building that is part of an architectural composition The cleaning of one building in a terrace can lead to a patchwork appearance; on a detailed level it can result in ragged edges where chemical washes or blasted grit have been sprayed onto the neighbouring structure The use of mechanical cutters such as angle-grinders to remove existing pointing should be avoided because of the potential to damage the arrises of the stones and widen joints as is the case in this illustration. Needing to rake out historic joints with power tools is often a sign that the pointing has not failed. Mechanical tools, used by specialist conservators, may be appropriate for the removal of later cement repointing Repointing which is inappropriately specified and carried out will not only damage the appearance of stone walling but may accelerate the decay of the stone. Sound old pointing should not be removed unnecessarily but, where repointing is unavoidable, the mortar used should generally be slightly weaker than the stone to avoid damage to the historic fabric

3. Page 123

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   Architectural Heritage Protection Guidelines for Planning Authorities 121 and would result in an unacceptable patchwork effect, damaging the architectural integrity of the group of buildings, permission should normally not be granted. But if the stonework of the group in general is being damaged by dirt deposits, the planning authority may consider it necessary to encourage the simultaneous cleaning of all the relevant buildings to the same specification. 8.3.20 The applicant should be able to justify the necessity of cleaning the stonework of a protected structure. The most frequent reason is on aesthetic grounds. Cleaning is also undertaken to identify necessary repair works or to remove encrustation which is thought to be facilitating decay. It should be considered whether the appearance of the building would be improved by cleaning, which may reveal previously hidden patches or repairs that were specifically coloured to blend with the dirtied appearance of the building. 8.3.21 While a well-executed programme of cleaning may expose detailing of high quality and reveal a building’s true architectural merit or can remove damaging encrustations, incorrect decisions can lead to irreversible damage being caused to the building together with a loss of fabric, architectural detailing and character. In some cases, an inappropriate cleaning method will accelerate decay in the stonework. Grit-blasting can be particularly problematic. The proposed cleaning methods should be examined in detail and the planning authority should inform itself on whether the proposed cleaning technique is appropriate and all relevant matters have been properly addressed. 8.3.22 Proposals for the removal of localised stains will require careful consideration. Such stains can include organic growth, graffiti or paint. The use of biocides to remove organic growth should be treated with caution as inappropriate use can cause damage to stonework. Graffiti and paint can be difficult to remove successfully from porous stone surfaces. A variety of methods such as poulticing, steam stripping and abrasion may be used but expert advice should be a requirement of such proposals. 8.3.23 A sample of each of the cleaning techniques should be approved by the planning authority before work commences. The applicant should be able to prove, to the satisfaction of the planning authority, that the proposed works have been specified by experts and would not damage the fabric of the building by: a) promoting outbreaks of wet or dry rot, b) creating surface staining due to the release of iron deposits within the stone, c) causing damaging salt migration through the stone or d) distorting the architectural detailing, removing tooling marks and blurring arrises. Brickwork IDENTIFYING SPECIAL FEATURES FOR PROTECTION 8.3.24 Brick has been used in the construction of buildings in Ireland for several hundred years. Early examples of brick walls used soft handmade bricks, sometimes of irregular shape. Where examples of these exist they should be identified and protected. Specialised pointing methods such as tuck-pointing, the use of coloured mortars and the like should also be noted. 8.3.25 As the nineteenth century progressed, the manufacture of bricks became industrialised and bricks were usually mechanically cut, resulting in sharp arrises. The use of various coloured bricks became popular and these were often used decoratively in patterned courses. Moulded bricks were extensively used in architraves, string courses, cornices, plinths and in decorative panels. Where these exist they will normally contribute to the architectural character of the wall and they should be protected. CHAPTER 8 WALLS AND OTHER STRUCTURAL ELEMENTS These adjoining houses of the 1770s both retain original brickwork. On the right, the brickwork has an applied red wash and penny-struck pointing; the brickwork on the left retains its original flush pointing, now needing repair Inappropriate grit-blasting or chemical cleaning methods may ultimately shorten the life of stonework by removing the protective skin of the stone, exposing it to greater environmental damage, or may damage the appearance of the stonework by blurring arrises, tooling or carved work, as has happened in this example

4. Page 124

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   CHAPTER 8 WALLS AND OTHER STRUCTURAL ELEMENTS Architectural Heritage Protection Guidelines for Planning Authorities 122 CONSIDERATION OF PROPOSALS AFFECTING BRICK WALLING Specification of repair works 8.3.26 Many of the considerations that apply to the repair of stonework apply equally to brickwork. Brickwork repairs need detailed specification and an applicant should be required to provide the planning authority with all necessary information to allow an assessment of the proposals. This information could include: a) the specification of any replacement bricks; b) a sample of the replacement brick; c) the specification and extent of any proposed repointing; d) the techniques to be used in carrying out the works, and e) the experience and expertise of the people who will be responsible for the work. 8.3.27 In some cases, the planning authority may need to seek specialist advice to ensure that all relevant matters have been thoroughly investigated by the applicant. Replacement of bricks 8.3.28 The replacement of individual decayed bricks may be permitted where bricks have been damaged or decayed to the extent that their structural integrity is in doubt. It should be a condition that decayed bricks are cut out in a way that causes the minimum disturbance to the surrounding sound bricks. If an unacceptable amount of disturbance is likely, the use of brick slips may be permitted as replacements rather than full-depth bricks, providing the structural stability of the wall is not compromised and the adhesion of the slips is guaranteed. 8.3.29 Any replacement bricks should match the original as closely as possible in size, durability, texture and colour. For example, where the original bricks are soft handmade bricks, the use of machine-made replacements are likely to be inappropriate. In special cases, it may be necessary to have new bricks made in order to achieve an appropriate match. Any replacements should be laid with the same bond, joint size and joint colour as the original. Where the brickwork is patterned or coloured, the replacement bricks should match the pattern and colours of the originals. 8.3.30 Matching second-hand bricks should normally only be used where they have been weathered similarly to the existing bricks and providing that the replacement bricks have not been taken to the detriment of another building. Mortar repairs to brickwork 8.3.31 Damaged brickwork can be repaired by patching using specialised mortars, a technique also known as ‘plastic repair’. Extensive mortar repair work is not appropriate in brick walls. The technique should normally only be permitted where small amounts of work are required and where specialists will carry out the work. Mortar repairs should not be permitted in cases where it is seen merely as an inexpensive alternative to brick replacement. 8.3.32 The applicant should be able to show that the specification of the work will not promote further damage of the brickwork. For example, the use of cement-based mortars will accelerate decay in many cases. Repointing of brickwork 8.3.33 Repointing which is poorly executed or uses unsuitable techniques or materials can cause physical damage to the fabric of the building, materially alter its appearance and substantially detract from its character and quality. A proposal to repoint a protected structure, which would materially alter its character, will require planning permission. The planning authority should make it a condition of permission that the work is carried out Where the repointing of historic brickwork is proposed, the specification of the mortar and the style of work to be used in repointing should be provided. Where specialist work will be required such as wigging and tucking, demonstrated here, the work should be undertaken by experienced personnel The decay of the soft handmade bricks of this façade has been accelerated by the use of extensive and poorly-executed cementitious mortar repairs coupled with strap pointing

5. Page 125

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   Architectural Heritage Protection Guidelines for Planning Authorities 123 by experienced people under the direction of a specialist with a working knowledge and experience of historic buildings. 8.3.34 Repointing should be considered a repair that replaces lost or damaged fabric with a compatible and appropriate mix (or series of mixes), material and appearance, provided that the existing pointing is not inappropriate or damaging to the brickwork. Comprehensive repointing of a structure is rarely necessary unless the existing pointing is causing damage to the brickwork or other fabric. It could be a condition that any sound pointing is left undisturbed, as it is an essential part of the fabric and character of a historic building or structure and should never be removed unnecessarily. 8.3.35 Visually, pointing should always be subservient to the brickwork and for this reason obtrusive pointing methods such as ribbon, weatherstruck or strappointing should never be permitted unless it is proven that that was the original design intention and not merely a previous unsuitable intervention. Where examples of pointing exist, such as tuckpointing or lime putty used in gauged brickwork, as much as possible of the original material should be retained and should not be lost in a comprehensive repointing of the wall. 8.3.36 Again, as with stonework, existing mortar should not be cut out with inappropriate mechanical cutters, such as angle-grinders, as these will inevitably damage the arrises of the bricks, possibly widen the joints and so damage the appearance of the brickwork. The use of mechanical tools in the hands of specialist conservators may be appropriate for the removal of later cement repointing. Brick cleaning 8.3.37 As with stonework, the cleaning of brickwork can materially affect the appearance of a protected structure or the character of an ACA. The potential of brick cleaning to cause irreversible damage means that where the works would materially affect the character of such a structure, these works will require planning permission. Unco-ordinated cleaning of buildings, which are part of an architectural composition, can create a patchwork effect, damaging the architectural integrity of the group of buildings. In such cases, permission should normally not be granted. But if the brickwork of the group in general is being damaged by dirt deposits, the planning authority may consider it necessary to encourage the simultaneous cleaning of all the relevant buildings to the same specification. 8.3.38 The method of cleaning a brick building should be considered carefully. In some cases, the cleaning method may in fact accelerate decay in the brickwork. On the other hand, a well-executed programme of cleaning may expose detailing of high quality and reveal a building’s true architectural merit. As with stone cleaning above, proposals for the removal of localised stains, such as organic growth, graffiti or paint, will require careful consideration. A variety of methods such as poulticing, steam stripping and abrasion may be used but expert advice should be a requirement of such proposals. 8.3.39 Before any works are undertaken, careful research and a full assessment are needed and the onus should be on the applicant to satisfy the planning authority that cleaning will benefit the protected structure and that the methods used will not damage its fabric or character. 8.3.40 The planning authority should approve a sample of each of the proposed cleaning techniques before work commences. The risk of damage to the fabric should be assessed. Unlike certain types of stonework, brickwork is usually unaffected by dirt deposits except in its appearance. Water-washing, if incorrectly used, may saturate the fabric and cause outbreaks of wet or dry rot within the structure or cause damaging salt migration through the brickwork. Inappropriate abrasive systems such as grit-blasting will damage the outer surface or fireskin of the brick and accelerate the decay process. Specialised pointing methods, such as tuckpointing, will be damaged by inappropriate cleaning processes. Timber IDENTIFYING SPECIAL FEATURES FOR PROTECTION 8.3.41 Timber is found as a structural element throughout traditional buildings whether as framing, posts, beams, lintels, wall plates, rafters or trusses. Timber pieces are also found set into masonry walls as CHAPTER 8 WALLS AND OTHER STRUCTURAL ELEMENTS The conservation work carried out to the left-hand house – new tuck pointing and cleaned brickwork – appears to have been well specified and executed, however the architectural integrity of the terrace as a whole may suffer from the patchwork effect of uncoordinated works

6. Page 126

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   CHAPTER 8 WALLS AND OTHER STRUCTURAL ELEMENTS Architectural Heritage Protection Guidelines for Planning Authorities 124 bonding and levelling pieces, fixing points or simply as filling. Early timber-framed external walls are extremely rare in Ireland and where they are found they should be identified and protected. Timber stud internal walls can be either structural in function, sometimes trussed, or acting as nonstructural partitions. 8.3.42 In addition to their interest as evidence of original or early structural systems, old timbers are of importance where they can be used, by means of dendrochronology (tree-ring dating) or by means of the construction method used, to date periods of construction. Where original or early timber structural elements exist, such as timber flitch beams, cruck trusses and other trussed construction methods, they should be identified and retained. CONSIDERATION OF PROPOSALS TO REMOVE OR REPLACE DECAYED STRUCTURAL TIMBER 8.3.43 While a great quantity of historic timber fabric can been lost through the processes of decay, a great deal more can be lost in the process of treating it. The appropriate treatment and repair of timber decay in old buildings involves careful detailing, experience and an understanding of the decay processes. The use of chemical treatments is no substitute for good detailing and workmanship. 8.3.44 The timbers used in structures built before the twentieth century generally came from slowgrowing, often virgin, forests and as such are a nonrenewable resource. This timber is usually denser (often having greater load-bearing capacity than modern timber), more durable and more resistant to fungal infection and insect attack. In many cases original timber elements can outlast pre-treated modern timber repairs exposed to the same decay factors. 8.3.45 Where timber is a significant part of the structure’s fabric, the applicant may be required to provide detailed independent survey reports and methodologies for dealing with timber decay issues in a way which would minimise the damage to, and loss of, historic fabric. 8.3.46 The removal of original or early timber from a protected structure should generally not be permitted or, where proven to be necessary, should be kept to a minimum. The removal of important timber structural elements or joinery simply as a precautionary measure against possible fungal infection should not be permitted. Where an unavoidable risk has been identified, monitoring can be used as an alternative to the removal of timber. The only justification for the removal of original or early timber should usually be where structural decay has occurred and repairs require its removal. This is normally confined to bearing ends. 8.3.47 Proposals may be made to remove large areas of render, plasterwork or other finishes in order to expose structural timber, often resulting in a significant loss of historic fabric. These proposals should not be permitted unless the applicant can prove there is good reason to suspect that significant decay has occurred to concealed structural timber. If concealed timber is present, but is not structural, a case can often be made for its retention in situ. Stripping large areas of wall plaster in the pursuit of concealed bonding timbers can often be avoided by simply tapping the plaster surface and listening for voids. Localised removal and replacement with a non-timber element can then be carried out where necessary. Fungal attack 8.3.48 Structurally significant timber decay is generally only found where the timber is embedded in, or is in contact with, saturated masonry. Timber decay fungi in buildings are commonly grouped into ‘wet rots’ which includes a range of fungal species and ‘dry rot’ (Serpula lacrymans) a single fungal species. Although the typical conditions in which each thrive and the patterns of decay vary, the remedial actions required are the same. In the recent past, Original or early structural timbers contribute to the character of a structure. Rare elements of structural timber, such as this seventeenth-century bricknogged partition, are extremely important and should be identified and protected The localised removal of bonding or levelling timbers within a masonry wall may be appropriate where there is good reason to suspect that they have significantly decayed. However locating these timbers and removing them can involve the destruction of large amounts of historic fabric particularly plaster

7. Page 127

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   Architectural Heritage Protection Guidelines for Planning Authorities 125 treatments of dry rot have tended to be very destructive of the existing fabric of buildings. These treatments often require the cutting out and destruction of all timber within a specified radius of the infection and the introduction of large amounts of fungicidal chemicals into the surrounding fabric. In light of a greater understanding of the processes of fungal decay in buildings, this type of treatment is now considered inappropriate. The removal of timber should be confined to that which is structurally decayed. 8.3.49 Proposed opening-up works and treatments that require the extensive disturbance or loss of fabric (such as ceilings, floors and finishes) and the widespread removal of uninfected timber should not be permitted and are not necessary to control a fungal attack. Dry rot requires water and masonry in order to decay timber. When the source of water has been removed, the fungus will die back naturally once the timber has dried out. 8.3.50 Where proposals are made to treat fungal attack within a protected structure, the applicant should be able to show that the sources of moisture (past and present) have been identified and that proposals have been made for remedial action such as the drying-out of masonry, ventilation, repair of structurally decayed timber and the isolation of existing and new at-risk timber, with a minimum disruption of the historic fabric. 8.3.51 Proposals to irrigate walls of any structure with fungicidal chemicals should be treated with caution. In cases of dry rot decay, the drying out of the structure, the provision of adequate ventilation and appropriate detailing of repairs will be sufficient to control the infection. Where the structure is difficult to dry out, for example where there are thick masonry walls, the detailing and monitoring of the moisture contents of critical timbers, localised ventilation and, occasionally, the use of dehumidification can control rot during the dryingout period. This may arise particularly in cases where the fabric of a building has been saturated as a result of fire-fighting or flood damage. Insect infestation 8.3.52 Only two types of wood-boring insect are commonly found in structures in Ireland: woodworm, which is the larval stage of a beetle (Anobium puncatum) and wood-boring weevils. Wood-boring weevil damage, unlike woodworm, is caused by the adult weevils. Conditions required for weevil damage include persistently wet timber partially (and often substantially) decayed by fungi. 8.3.53 Wood-boring insects require timber of a high moisture content to survive, so the elimination of dampness and the provision of appropriate ventilation should usually be sufficient to control the infestation. Appropriate remedial action to deal with wood-boring insect damage is to cut out and replace structurally affected timber and to isolate replacement timber from the moisture source, combined with clearing dirt and debris from relevant voids and the provision of ventilation to protect against future infestation. Mud and sod walling IDENTIFYING SPECIAL FEATURES FOR PROTECTION 8.3.54 Unbaked earth was used throughout Ireland in the construction of vernacular buildings, usually where free stone was not available in sufficient quantities or quality for the construction of rubble walls. Mudwalled houses can be substantial single or twostorey buildings. Clay from the subsoil was mixed with chopped straw, water and other materials to form the building material. The mud walls were constructed off a plinth of stone and the walling built up in layers, sometimes using timber shuttering to support the work. Often the cross walls of the house containing the chimney stacks were built in stone or brick but they could also be constructed of wickerwork plastered with daub. Clay and mud were also used as mortar materials. CHAPTER 8 WALLS AND OTHER STRUCTURAL ELEMENTS Where an outbreak of fungal attack in timber has been identified, the removal of historic fabric should be confined to timber directly infected by the rot or structurally weakened by it. Once the source of water has been removed and adequate ventilation provided, the fungus will die back naturally, thus avoiding the need for the wholesale stripping out of timber Where timbers contain flight holes from past infestation by wood-boring insects, it is important to establish whether or not the infestation is current. In this case a furniture beetle, or woodworm, is visible on the surface of the timber beam, indicating ongoing attack

8. Page 128

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   CHAPTER 8 WALLS AND OTHER STRUCTURAL ELEMENTS Architectural Heritage Protection Guidelines for Planning Authorities 126 8.3.55 Because earth walling was traditionally covered with lime-based roughcast or limewash coatings and sometimes a stone facing, the construction of these buildings may not always be readily identifiable. Their increasing rarity means that the preservation and maintenance of the surviving examples is extremely important. 8.3.56 Sod walling is another form of vernacular walling where trimmed lumps of topsoil were used as building blocks. These blocks were sometimes pegged together or bound together with a clay mortar. Examples of this type of construction are extremely rare and any surviving examples should be identified and protected. CONSIDERATION OF PROPOSALS AFFECTING MUD AND SOD WALLING 8.3.57 Alterations or extensions, that might endanger the stability of an earthen structure should not be permitted. Where alterations or repairs are proposed to mud-walled structures, expert advice needs to be taken by the applicant. 8.3.58 The strength of mud walling is dependent on its moisture content. Consequently, the introduction of damp-proof courses should be avoided as these may lead to a drying out of the wall and to instability in the structure. For the same reason, strong and impervious cement renders or plasters should not be permitted to the exteriors or interiors of these walls as these damage the walling material’s ability to breathe and can lead to its failure. 8.3.59 The addition of impervious building materials, such as the insertion of bricks and concrete blocks into the fabric, should always be avoided as these can undermine the structural stability of the walling. Iron and other metal structures IDENTIFYING SPECIAL FEATURES FOR PROTECTION 8.3.60 Wrought or cast iron are found in use as structural elements in a variety of protected structures, including industrial buildings and conservatories. Because of technical advances during the nineteenth century in the production of iron, iron structural elements were used extensively in many Victorian industrial buildings such as railway stations and warehouses. Wrought iron has a high tensile strength and so tends to be found in beams. Cast iron on the other hand, has little tensile strength but considerable compressive strength and so was commonly used in posts and columns. Both forms of iron, and a combination of the two, were also used in architectural embellishments such as balconies, verandas, cresting and railings. Mud walling was generally built up in layers or occasionally using unbaked blocks of clay. Mud-walled buildings are not always readily identifiable as they were usually finished with a roughcast render coating of mud or lime mortar. It is in the nature of the material that mud-walled buildings tend to decay rapidly unless well-maintained and prompted repaired when damaged Structural ironwork is found in a large range of building types where it is usually clearly identifiable. However, cast-iron elements were also formed in imitation of masonry, as in this balustraded bridge parapet, and the material used may not always be obvious The early twentieth-century cast in situ concrete repair to this mud-walled house at Mayglass, Co. Wexford was the subject of careful consideration during recent conservation work, but was left in place once stabilised. Unbaked brick was used elsewhere for repairs to the walling

9. Page 129

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   Architectural Heritage Protection Guidelines for Planning Authorities 127 CONSIDERATION OF PROPOSALS AFFECTING IRON STRUCTURES 8.3.61 In situ repairs will usually cause less damage to historic ironwork than dismantling and re-erecting. However it may be necessary for the planning authority to permit partial dismantling and reerection of an iron structure in cases where movement or distortion of the structure has occurred, in order to effect repairs. Dismantling may also be necessary in order to apply rust treatment to inaccessible areas. 8.3.62 Where dismantling of an iron structure is permitted, it should be conditional on the structure being recorded in detail before work commences by means of drawings and photographs, with each element tagged and numbered and cross-referred to the relevant drawing. As much of the existing material as possible should be retained and consolidated rather than renewed. Additional and appropriate material may be added, where necessary, to reinforce or to support the existing material where this would not adversely affect the fabric or appearance of the protected structure. 8.3.63 When permitting the removal of paint prior to repair, it must be realised that this action eradicates the paint history of the ironwork, where this survives, thus making it impossible thereafter to determine the original or earlier colour schemes. Where the planning authority considers important evidence of an earlier paint scheme may exist, it could be a condition of permission that a small area of ironwork be left unstripped or a proper paint analysis carried out before an appropriate method of paint stripping takes place. 8.3.64 Where small elements of ironwork are missing, a case could be made for restoration or replication of the missing element. However, such restoration should be based upon firm evidence of the original element using old photographs, drawings, or other reliable information and should not be conjectural. Where it is necessary to replace wrought-iron structural members, recycled wrought iron should be used or new wrought iron obtained, if available. This is preferable to introducing a replacement material, such as mild steel with its different physical properties, such as thermal expansion coefficient, which may be potentially damaging to the structure. Mass concrete and reinforced concrete structures IDENTIFYING SPECIAL FEATURES FOR PROTECTION 8.3.65 Mass concrete has been used for construction in Ireland since the middle of the nineteenth century. Although the use of iron, and later, steel rods to strengthen concrete began in the eighteen-fifties, the use of reinforced concrete in Ireland is primarily found in buildings of the twentieth century. 8.3.66 Both mass and reinforced concrete were commonly used in the construction of engineering structures such as bridges. In the twentieth century, mass concrete was often used as a walling material which was commonly rendered or clad. Concrete was also CHAPTER 8 WALLS AND OTHER STRUCTURAL ELEMENTS Early mass- and reinforcedconcrete structures, as well as early blockwork and cast or reconstituted ‘stone’ structures may be of technical interest. This silo of 1905 is constructed of reinforced concrete using the pioneering Hennebique technique and is one of the few such structures surviving in Ireland While it may sometimes be necessary to carefully dismantle an ironwork structure for repairs, some structures may consist of iron-clad sections on timber and masonry supports and may be more difficult to successfully dismantle and reassemble

10. Page 130

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    CHAPTER 8 WALLS AND OTHER STRUCTURAL ELEMENTS Architectural Heritage Protection Guidelines for Planning Authorities 128 used as a self-finished material sometimes boardmarked from the shuttering to give the finished concrete a textured appearance. Early mass or reinforced concrete structures will be of interest and should be identified and may often be worthy of protection. CONSIDERATION OF PROPOSALS AFFECTING CONCRETE STRUCTURES 8.3.67 Where repair works are proposed to concrete structures it is important to ensure that the applicant has carried out adequate investigations to determine the cause and extent of damage. An incomplete understanding of the mechanisms of decay can lead to inadequate, or possibly damaging, repairs. 8.3.68 Where voids in the surface of exposed concrete allow water to enter and cause spalling, these will need to be filled. However, superficial methods of repair to concrete, such as spraying with new concrete, should generally not be permitted without assessing and treating the underlying problem of rusted reinforcement. Spraying on new concrete may be visually unacceptable where it will alter the profile of the concrete components of a protected structure. Specification and methods of repair should be approved by the planning authority prior to works commencing. 8.4 Cladding Materials Plain and roughcast render IDENTIFYING SPECIAL FEATURES FOR PROTECTION 8.4.1 Plain and roughcast renders are traditional coatings applied to rubble, brick and other structures throughout the country and usually form an integral part of a building’s weathering system as well as its designed appearance. 8.4.2 Roughcast renders were the traditional external coatings applied to rubble-walled buildings. These were made of a mixture of lime putty and sand with other additives, including animal hair, creating a relatively soft and porous render which was applied by throwing the mixture at the wall resulting in a gentle, undulating finish. Roughcast render was usually finished with layers of limewash, reapplied on a regular basis. Where original or early limebased roughcast finishes are identified, they may be worthy of protection. 8.4.3 The late eighteenth and nineteenth centuries saw much experimentation with render mixes leading to the development of a number of patented renders including oil mastic stuccoes and Roman cement. The patenting of Portland cement in England in the early nineteenth century allowed for the production of harder, more brittle coatings which could be applied by trowel and finished to provide a smooth surface. 8.4.4 Plain renders are found on buildings throughout the towns of Ireland and often on the minor elevations of high quality ashlar or brick-faced buildings. Plain render is a harder and smoother material than roughcast render and often included the use of cement. In many cases, the render was ruled and lined out to imitate the pattern of ashlar blocks. The repair of concrete structures should be carried out so as to resolve the underlying problem without a visually obtrusive result. In this illustration the repair to the reconstituted ‘stone’ will tone down in time although the strap repointing is inappropriate Render is a traditional coating which contributes both to the weathering performance and appearance of a structure. This house has been partially faced in Roman cement in imitation of rusticated ashlar and, while not the original finish, clearly contributes to its character

Source Department of Arts, Heritage and the Gaeltacht: Architectural Heritage Protection: Guidelines for Planning Authorities (2011) · Licence the publisher's termsText read from the publisher’s PDF; tables, maps and drawings do not survive as text, and page numbers are the PDF’s (its first page is 1). Check the original before relying on a passage.