Edwardian Pebbledash and RoughcastJonathan Taylor
The mere mention of the word ‘pebbledash’ can silence a conservationist at 50 paces. The term is inextricably associated with the very worst excesses of the ‘home improvement’ industry. Acres of these harsh cementitious renders enveloped the facades of humble terraced houses in the late 20th century, irrespective of whether the underlying surface was brick or stone, plain or elaborately decorated, Georgian or Edwardian. The original surface details which give these buildings their character were obliterated, and the alteration was usually accompanied by the replacement of the sash windows with plastic or aluminium designs, often widening the openings. The result, which can be found in city centres throughout the UK, is the total annihilation of every last vestige of historic character. However, all that aside, there is another side to this material which is all too easily overlooked. Pebbledash was also an essential element in the palette of the Arts and Crafts movement. WHAT ARE THEY?Pebbledash and roughcast are forms of render in which the top coat is roughly textured by pebbles or stone fragments. As the terms are used today, they each have different meanings. For pebbledash, clean material is thrown at the freshly plastered surface then pressed in, so the colour of the material is visible. For roughcast, on the other hand, this material is mixed with mortar and then thrown at the surface, so all the material is coated with the mortar. This produces a slightly softer texture and the surface is usually limewashed.
In the Edwardian period it is unlikely that these distinctions existed, and the terms pebbledash and roughcast were widely used to describe the same thing. William Millar, in his epic Plastering – Plain and Decorative, which was first published in 1897 (reprinted by Donhead in 1998), gave pebbledash as another name for roughcast, and made no distinction between the two. He also commented that this form of render was known in Scotland as ‘harling’, as it still is today. ‘Cast’, ‘dash’ and ‘harl’ in any case mean much the same thing, and as with any vernacular craft, materials would have varied from one region to another. Millar’s invaluable guide gives a contemporary account of roughcast (or pebbledash) at the end of the Victorian era. The wall would first have been given a coat of ‘strong-haired coarse stuff’, that is to say a mortar of lime or hydraulic lime and aggregate with a high proportion of animal hair. This would then have been scratched to provide a good key. Next, when this coat had dried, a second coat of the same material, ‘well knocked up and of even consistency’ would have been applied, laid to an even surface ready for the shingle or other material to be dashed on. The material, he advised, should be well washed, passed through a quarter- to half-inch sieve, mixed with ‘hot lime (hydraulic for preference)’ and water in a tub. This suggests that quicklime was slaked with the pebbles, shale or gravel in it. When the second coat of render was ready, the material would then have been thrown quickly and evenly onto the soft surface using ‘a “scoop” or hollow trowel’, starting from the top and working downwards. The principal component of the finished surface is thus the pebbles or stone fragments with a thin coating of binder. For exposed environments Millar recommended the use of Portland cement rather than lime. Examples from this period which have survived would suggest that this approach was commonly followed, although it seems likely that most examples from the Edwardian period onwards contain Portland cement either on its own or as a gauged lime mortar. Pebbledash was an ideal finish for a Portland cement render. When production was perfected in 1852 and the material began to be used widely, it was found that renders made with the material tended to crack almost immediately. This was caused by the trowelling required to produce a smooth finish, since this increases the proportion of both small particles and moisture at the surface. However, a roughcast or pebbledash requires only the minimum of trowelling, and pressing the course stone aggregate into the surface consolidates it, minimising the risk. The result is a hard, durable surface, easily capable of binding a pebbledash coating. HISTORIC USERoughcast, as conservationists prefer to call the earliest material, probably has a history as old as lime mortar itself. It is widely found on medieval buildings, particularly in the rendered panels of timber-framed houses, but it can also be found on stone buildings, often with stone quoins and window surrounds projecting beyond the render. In some cases the pebbles or stone fragments are pressed in flush to form a rough, uneven surface. In other cases the stone material is left deliberately proud to create a sugary texture, often acting as a foil for smooth features such as window surrounds and quoins. It is this latter technique which is so commonly seen in Scotland, not only on medieval castles and tower houses, but also on post-medieval houses and stately homes, continuing in an almost unbroken tradition through to the Arts and Crafts movement, and buildings such as CR Mackintosh’s Hill House. Roughcast renders continued as a vernacular tradition in England too, and the finish became fashionable in the cottage ornée style of the early 19th century, and in the Tudor domestic style of architecture of the late 19th century, particularly as the background for half-timbered gables. However, it was probably the work of Richard Norman Shaw more than anything else that was responsible for its popularity at the end of the 19th century. The Queen Anne style that he developed in the 1860s and ’70s was enormously influential for the next 30 years, typified by his work at Bedford Park, such as the Tabard Inn (1880). Here, the asymmetric composition of steeply pitched roofs, jettied floors, small-paned windows and rough textures evoke an atmosphere of cosy cottage comforts with roaring log fires, albeit on a grand scale. The wall surfaces are a patchwork of textures, with areas of solid brickwork, roughcast renders and tile-hung gables. The Arts and Crafts movement that ensued adopted the palette of materials and forms popularised by Shaw, including tall chimneys, small-paned windows, clay tiles, and roughcast or modern pebbledash. The list of exponents included architects like CFA Voysey, Lutyens, Baillie-Scott, and Charles Rennie Mackintosh, and by the turn of the century the material adorned the homes of the avant-garde and the rich, as well as those of the residents of garden cities and the expanding suburbs. Pebbledash and roughcast initially proved popular because they offered texture and because they were seen to be traditional craft techniques. However, their revival flourished because they were cost effective, and they were ideal for use in the new suburban developments of the late 19th century. At Port Sunlight, a development much influenced by Bedford Park, the aim was to create affordable housing with the delights of the countryside. Roughcast and pebbledash enabled solid, brick-thick walls to be constructed of common bricks, relying on the hard, impervious render to keep out the damp. This garden suburb was created in the late 19th century by William Hesketh Lever (later Viscount Leverhulme) in the Wirral, Cheshire to house the employees of his soap factory, Lever Brothers (now part of Unilever). Here pebbledashed buildings included a school, a cottage hospital and civic buildings, as well as hundreds of houses of varying sizes, all laid out with broad tree-lined streets. Architectural styles were combined with complete eclecticism, with Edwardian Queen Anne style jostling shoulders with pastiches of local timber-framed Elizabethan buildings like Little Moreton Hall or Sussex tile-hung and jettied medieval buildings.
Similar examples of pebbledashed suburban housing can also be seen in Hampstead Garden Suburb. This pioneering experiment in social housing attracted some of the most influential architects in the country, including Lutyens (who also designed one terrace in Port Sunlight) and Baillie Scott. The architectural styles found at Port Sunlight and Hampstead Garden Suburb were replicated with endless variety through the suburban developments springing up around the major conurbations across the country. Seen from today’s perspective, and under the influence of our own tastes, pebbledash works well when used sparingly and with other materials such as tile-hanging and brickwork. Where the material covers whole buildings it needs robust detailing to make it work, and many smaller buildings with weak detailing can appear drab as a result. Nevertheless, there are many superb examples of buildings plastered entirely with unpainted pebbledash, such as Voysey’s Broadleys on Lake Windermere (1898-9) and his own house, The Orchard, Chorleywood, Hertfordshire (1899-1900). In both cases the walls of the first floor almost disappear under the low-spreading roofs, and large heavily mullioned windows break up the remaining mass of render into small elements of surface texture. Perhaps one of the most stunning examples of the period was Edwin Lutyens’ magnificent stately home at les Bois des Moutiers, Varengeville-sur-Mer, France. Here again all the external masonry is plastered with pebbledash, including the soaring chimneys. Here, however, the expanses of unpainted pebbledash are much larger, and it is the richness of its detailing which lifts it, including its jewel-like small-paned oriel windows in particular. THREATSThe principal threat facing Edwardian pebbledash architecture is inappropriate alteration. Through the mid- to late-19th century the architecture was derided by critics. In The Pattern of English Building, Alec Clifton-Taylor, writing in 1962, commented that ‘one often recoils with acute distaste from [pebbledash’s] coarse and lumpy texture and its drab yellow-brown colour’. These views were widely shared by a generation reacting to the architecture of the previous generation.
Even now, few Edwardian suburban developments are protected by conservation areas, and as a result, much of this architecture has been destroyed by inappropriate alterations. As the success of Edwardian pebbledash architecture is heavily dependent on strong detailing, including leaded lights and mullioned windows in particular, the aesthetic changes dramatically when these are replaced by large-paned double-glazed windows. Tile hanging is also often replaced by other materials when the nails supporting them start to rust through, and paint is often applied to disguise repairs, or to provide an alternative to the ‘drab yellow-brown colour’. Structurally, the material performs extremely well where the underlying brickwork has been constructed of the same cement-rich mortars, as the structure is relatively rigid, and the render coat does not have to accommodate as much movement as it would over traditional masonry with soft lime mortar. Nevertheless, cracks can appear, particularly as a result of structural movement. Being impervious, the material is also vulnerable from trapped water. Parapets and Queen Anne gables are particularly prone to saturation from rain absorbed through the copings and through the back face where inadequately protected by flashing. Trapped water can freeze, causing the render to fall away in sheets. Salt crystallisation may also occur around cracks as water evaporating here leaves a build up of salts, causing salt crystals to grow in the substrate. CONSERVATION AND REPAIRThe repair of Edwardian pebbledash and roughcast is still a relatively new area for conservators. The standard solution to cracks and coat separation (either the outer coat or the base coat from the substrate) is to hack back to sound material, leaving edges slightly undercut where possible to improve the key. Tapping with a wooden implement such as the handle of a chisel will help to identify sound areas. Brickwork joints are then raked back to provide a key for the new mortar which is applied in two coats to match the existing.
At Port Sunlight, conservation officers at Wirral Council recommend that, for a moderately strong and porous background, a typical mix for dubbing out and the undercoats would be Portland cement, lime (hydrated high calcium lime) and sand, in the proportions 1:1:6 by volume. The mix for finishing coats would be cement, lime and well graded sand (to BS 1199), in the proportions 1:2:9 by volume. For the pebbledash, stone which has been selected to match the original in size, colour and type, should be dashed on evenly using a scoop while the topcoat is still soft and then firmly tamped into the render to give an even-textured appearance over the whole wall face. Where unpainted pebbledash is concerned, the appearance depends on the colour and texture of the mortar, the ratio of stones to mortar, and the appearance of the stones themselves. It is therefore difficult to achieve a good match, and repairs are often highly visible. Understandably, owners often find a patchwork affect difficult to accept, and as a result there is a tendency to overpaint repaired pebbledash, substantially changing the character of the building and its historic integrity. Pebbledash repairs must therefore be carried out by skilled conservators and backed up by mortar analysis. In some cases it may be possible to avoid repairs by injecting with a fine hydraulic grout or other consolidant. Where unpainted pebbledash is suffering from surface cracks, layers of dirt may hide some cracks and cleaning may be necessary. The selection of the most appropriate method of cleaning will depend on the nature of the dirt layer, but generally the use of solvents and degreasants in conjunction with gentle washing are likely to be the least damaging, provided that care is taken to avoid saturating the material. Edwardian roughcast, since it is based on hard cement-rich mortars, displays much the same problems as pebbledash. However, it is usually painted over, and so repairs are more easily hidden.
Before carrying out any repair, it is important to consider the cause of the problem. If the original detailing and the original materials are at fault, repairing as found may be inadvisable. For example, is a flashing required to prevent moisture ingress? Or is the use of a dense cement-rich render itself causing the problem? There are many cases where really important historic buildings have been treated with a cement roughcast or pebbledash in the 19th or 20th century which is now causing problems. Damp finds its way in through cracks and is then trapped, causing the underlying structure to deteriorate. In a situation such as this, where a modern cement render is obviously inappropriate, the natural reaction would be to replace the render with a softer and more porous lime-based alternative that can allow the building to breathe. However, cement renders tend to adhere to the substrate extremely well, and separating the two can result in the loss of the underlying face, causing more damage than it prevents. It is therefore essential to start with a test panel to determine whether complete removal is a practical solution. There are many cases, from medieval church towers to fine Georgian terraces, where the decision has been taken by conservators to leave a cement-based render in situ, and to maintain it as a waterproof coat rather than risk removing it. Pebbledash and cement render have been widely criticised in recent decades for being ugly, too hard, impervious and highly damaging to historic fabric. However, as this article shows, they are an important feature in the architectural vocabulary of the Edwardian period, and original examples deserve better understanding and careful conservation.
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The Building Conservation Directory, 2009 AuthorJONATHAN TAYLOR is the editor of The Building Conservation Directory and a co-founder of Cathedral Communications Limited. He studied architectural conservation at Heriot-Watt University, Edinburgh and has a background in architectural design, conservation and urban regeneration. JOANNE STOREY of Wirral Council kindly advised on repairs at Port Sunlight. Further informationRELATED ARTICLES RELATED PRODUCTS AND SERVICES
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