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Walls partly or completely of stonework one stone thick can be found in most areas where large building stone predominates, notably in Scotland and South West England. Single walls are nearly always built of field clearance stone, as opposed to quarried stone, and the rock type is usually igneous, with granite the most common type. Because of the size of the larger boulders, a team of two wallers is usually needed. Take great care with moving large stones (Chapter 4). There are two main styles of single walling. The 'single' has single stonework throughout. The 'half-single' is built double in the lower part, with the upper part single, and is widespread across much of Scotland. The half-single probably developed as a way of using both large and smaller stones in the same wall. For the same reason, sections of single wall are sometimes mixed in with double, a style known as 'butt and hudd' (Chapter 11). Singles are rarer than half-singles in Scotland, being mainly associated with granite areas such as the South West and parts of the North. In Aberdeenshire granite double walls predominate. As single walling is characteristic of Scotland, the following information concentrates on Scottish methods and terms. To distinguish between single dykes and 'standard' walls the Scots refer to the latter type of stonework as 'double' or 'doubling', as it has two skins of stone. A half-dyke is often termed a Galloway dyke, the history of which is discussed in Rainsford-Hannay (1972) and Prevost (1957). Single dyking has several advantages over double. It is simpler and faster to build and repair, and generally uses less stone for a given height. It requires tough coarse-grained stone such as granite in order to bind properly, and the style is a good use of this type of stone. Single dyking is surprisingly stable, but looks so unsteady that all stock, including the notoriously adventurous black-faced sheep, are supposed to be deterred from climbing it. Single and half-dyking require less hearting than a double wall, and regular topstones are not required. Single dyking does not however give as much shelter as double stonework, because of the gaps between the stones. Dyking procedureDismantlingGenerally the dyke is dismantled to one side only, leaving a working space of about 3' (900mm), although larger stones might be spread on both sides. Stones should be reasonably well spread to give good access to individual stones, especially larger boulders. Set any pins or wedges to one side. FoundationThe foundation of single dykes can either be double stones as for 'standard' double walls, single stones or a mixture of the two. A double foundation provides a good level start to the wall and disperses weight well, sometimes aided by a small scarcement (Chapter 11), and is preferred by many single dykers. It also uses up some of the stone which, in single walling terms, is rather small. For a double foundation follow the procedure given in Chapter 6. For a single foundation, dig the trench to an accurate line, and then set the stones centrally by eye. Occasional long stones should be accommodated by widening the trench at that point, and setting the stone so that it extends equally on both sides. It's permissible to 'trace' stones, provided that they completely span the wall, or half span it. A three-quarter span is no good, as it leaves a gap too narrow to place a secure stone.
ProfileWhilst the profile of single walls is 'A' shaped, as with double walls, the width of the single stones in any layer varies, and consequently the face is not flat and frames are not appropriate. BuildingStones are set 'upright', like coping.
The pattern is generally determined by the need to maintain very good contact between stones. Fairly regular stones can be layered and resemble coursing. Where the stone is less regular the pattern is more random, but the stones are still set upright. Generally the size of stone decreases higher up the wall, but the location of any individual stone is determined more by its fit across the wall than its height, as care needs to be taken to maintain the overall 'A' shaped profile. 'Taller' stones are thus often placed on top of 'shorter' ones. As with a doubled wall, work should be sequential, completing one layer before starting on the next. The techniques are in many respects similar to those of clawdd construction (Chapter 8), with the stones set vertically on edge and jammed together, or like setting rows of topstones on top of each other. Essentially the technique is 'upside down' compared to doubled walling, where the rule for each stone is generally 'flat side down, irregular side up'. Single walling is stronger if the irregular side is down, fitting into gaps and dips, with Keep the following in mind when placing each stone: a The longest face of the stone should be set across the wall. This rule should only be broken for very long stones which still span the width of the wall, as in the example from the Isle of Bute (Chapter 11). PinningPinning of single walls is subject to some debate. Most old single walls have many gaps which are not pinned. Some wallers claim this was deliberate, in order to create a 'fragile and tottering appearance' (Rainsford-Hannay, 1972) that would discourage sheep from jumping. It's claimed that sheep won't try to jump a wall which they can see through. Other wallers maintain that there would have been extensive pinning originally, but that much has worked loose during settlement. The 'belt and braces' approach is favoured by some wallers today, arguing that as the wall settles it will grip more tightly the pins that are needed, and the others will slip out anyway. Others claim that the real skill lies in building a strong but fragile-looking structure, without too much pinning. Pinning is carried out as for other walls (Chapter 11), usually pinning each section as you build. CopingCoping is nearly always the level top type (Chapter 11). The line for the top of the coping is normally set up before the layer preceding the coping stones is laid on the wall. This allows the stones in this layer to be chosen to give the right height for the available coping stones to fit. Normally a level finish should be avoided for the layer below the coping, unless the coping stones are of unusually uniform size. Any taller coping should be used in gaps or dips, and occasionally very large stones are used to 'jump' from the preceding layer to the top of the cope. This helps to promote a tighter cope, as it provides a solid stone against which the others can key.
Avoid sloping taller coping to achieve the correct finished height, unless it is held by a complementary stone.
Nearly all wallers agree that every nook and cranny between the coping stones, and between the cope and the preceding layer, should be pinned, as the cope stones rarely sit as well as they would on a doubled wall top. Regardless of the care taken though, the coping is relatively fragile, and so 'scare' fences of one or two strands of barbed wire alongside the coping are common in cattle areas. Further considerationsWhilst most stones are set vertically, awkward shapes can be sloped provided this is done to make them sit solidly, and that good contact is maintained with neighbouring stones. Large stones are sometimes set horizontally, although there is a tendency for them to wobble on any slight irregularity. They need to be matched carefully to the layer below, either 'very flat on very flat', or of a suitable shape to fit any irregularities. Although it's preferable to avoid running joints between layers, it's more important to ensure that each stone sits solidly and has good contact with its neighbours. The principles are similar to those for cloddiau (Chapter 8). For other considerations see 'general points' below (Chapter 11). All content copyright © 1986-2008 BTCV Ltd. Registered charity No. 261009 |
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