Roughcast or pebbledash is a coarse plaster surface used on outside walls that consists of lime and sometimes cement mixed with sand , small gravel , and often pebbles or shells. 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. 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. 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. This exterior wall finish was made popular in England and Wales during the s, when housing was in greater demand, and house builders were forced to cut costs wherever they could, and used pebbledash to cover poor quality brick work, which also added rudimentary weather protection.
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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. Those jagged little stones gleam from the walls of semi-detached houses in the suburbs of almost every town and city in Britain, from Birmingham to Glasgow to Swansea. 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.
He studied architectural conservation at Heriot-Watt University, Edinburgh and has a background in architectural design, conservation and urban regeneration. Loading comments… Trouble loading? In other projects Wikimedia Commons. Roughcasting incorporates the stones in the mix, whereas pebbledashing adds them on top.
Grey, lumpy, impossible to remove – but pebbledash isn’t all bad | Life and style | The Guardian
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. Where unpainted pebbledash is suffering from surface cracks, layers of dirt may hide some cracks and cleaning may be necessary. The wall surfaces are a patchwork of textures, with areas of solid brickwork, roughcast renders and tile-hung gables.
Brickwork joints are then raked back to provide a key for the new mortar which is applied in two coats to match the existing. Steve Cadman, on Flickr.
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.
A Tudor style semi in Brook Street, Port Sunlight by Grayson and Ouldwith leaded lights, clay tile hangings over a pebbledash ground floor and tall pebbledash chimneys. Pebbledash and roughcast initially proved popular because they offered texture and because they were seen to be traditional craft techniques.
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. Here and on the Voysey-esque elevation beyond by CH Reilly, the surface appears to be an original roughcast, rather than a pebbledash which has been painted. 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.
Grey, lumpy, impossible to remove – but pebbledash isn’t all bad
The principal threat facing Edwardian pebbledash architecture is inappropriate alteration. Being impervious, the material is also vulnerable from trapped water. 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 also an essential element in the palette of the Arts and Crafts movement.
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.
pebbleeash For example, is a flashing required to prevent moisture ingress? Pebbledash repairs must therefore be carried out by skilled conservators and backed up by mortar analysis.
Edwardian Pebbledash and Roughcast
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. These views were widely shared by a generation reacting to the architecture of the previous generation.
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. Understandably, owners often find a patchwork effect 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. Pebbles were dredged from the seabed to provide the building materials needed, although most modern pebbledash is actually not pebbles at all, but small and sharp flint chips, and should correctly be called Spar dash or spa dash.
For pebbledash, clean material is thrown at the freshly plastered surface then pressed in, so the colour of the material is visible. Show 25 25 50 All. Nevertheless, cracks can appear, particularly as a result of structural movement.
For exposed environments Millar recommended the use of Portland cement rather than lime. The modern variety is a mixture of sand, cement and pebbles or aggregate crushed stonesapplied to the exterior of houses to protect them from the vagaries of British weather.