Dry stone
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Dry stone is a building method by which structures are constructed from stones without any mortar to bind them together. The structure is supported by a unique construction method of the outer weight pushing inward toward the wall core; the stones must be carefully selected by shape to ensure that they have a significant contact surface area with their neighbouring stones and thus do not wiggle or slip. Dry-stone technology is best known for wall construction, but dry stone buildings, bridges, markings and other constructions are also abundant.
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[edit] Dry stone walls
A dry-stone wall, also known as a dry-stone dyke, drystane dyke, dry-stone hedge or rock fence is a wall that is constructed from stones without any mortar to bind them together. The wall is held up by a special construction method and by its own weight, and the stones must be carefully selected by shape to ensure that they have a large contact surface area with their neighbours and so do not slip. Such walls are used both in building construction and as field boundaries.
[edit] Location and terminology
Terminology varies regionally. When used as field boundaries, dry-stone structures are often known as dykes, particularly in Scotland, and to some extent in the North of England. Dry-stone walls are characteristic of areas of Britain and Ireland where rock outcrops naturally or large stones exist in quantity in the soil. Dry-stone dykes are characteristic of Scotland, rural parts of Ireland, and of the upland countryside of England and Wales. They may also be found in the Apulia region of Italy as well as New England in the United States. Such constructions are common where large stones are plentiful (for example, in The Burren) or conditions are too harsh for hedges capable of retaining livestock to be grown as reliable field boundaries. Many thousands of miles of such walls exist, most of them centuries old. This article will generally use the word "dyke" to describe them. The term "wall" will be used here for a dry-stone structure that is part of a building, or part of a dyke.
In the United States they are common in New England and are a notable characteristic of the bluegrass region of central Kentucky, where they are usually referred to as rock fences. This type of structure is common in areas with rocky soils, such as New England, Central Kentucky, and the Napa Valley in north central California. The technique of construction was brought to America primarily by Scots-Irish immigrants
Similar walls are also found in the Swiss-Italian border region, where they are often used to add the missing sides of the natural covered spaces under the large natural stones. Dry stone roofs are also common here, resulting the complete dry stone buildings. Near a home it is not uncommon to find artwork embedded in the drystone wall in this locale. (photo)
Dry stone wall construction was known to Zulu tribes in southeastern Africa as early at 1350 to 1500 AD. When some of the Zulu migrated west into the Waterberg region of present day South Africa, they imparted their building skills to Iron Age Bantu peoples who used drystone walls to improve their fortifications.
In Peru in the fifteenth century AD, the Inca made use of otherwise unusable slopes by drystone walling to create terraces. They also employed this mode of construction for free-standing walls. Their ashlar type construction in Machu Picchu uses the classic Inca architectural style of polished dry-stone walls of regular shape. The Incas were masters of this technique, in which blocks of stone are cut to fit together tightly without mortar. Many junctions are so perfect that not even a knife fits between the stones
[edit] Construction
There are several methods of constructing dykes, depending on the quantity and type of stones available. Most dykes are constructed from stones and boulders cleared from the fields during preparation for agriculture. In areas where stones are plentiful, double wall dykes are preferred but where stones are scarcer, single wall dykes may be made. If the area contains boulders, boulder dykes will often be constructed. Boulder dykes are a type of single wall dyke in which the bottom row consists of boulders, upon and around which smaller stones are placed.
A double wall dyke may be constructed by placing two rows of stones along the boundary to be walled. The rows are basically large flattish stones. Smaller stones may be used as chocks in areas where the natural stone shape is more rounded. The walls are built up to the desired height layer by layer, and at intervals, large tie-stones are placed which span both walls. These have the effect of bonding what would otherwise be two thin walls leaning against each other and greatly increase the strength of the dyke. The final layer on the top of the dyke also consists of large stones, called cap stones. Like the tie stones, the cap stones span the entire width of the dyke and prevent it breaking apart.
Single wall dykes work best with flatter stones. Ideally, the largest stones are be placed at the bottom and the whole wall tapers towards the top. Sometimes a row of capstones completes the top of a wall, with the long rectangular side of each capstone perpendicular to the wall alignment.
Another variation is the "Cornish Hedge", which is a stone-clad earth bank topped by turf, scrub or trees, and characterised by a strict inwards-curved batter (the slope of the 'hedge'). As with many other varieties of wall, the height is the same as the width of the base, and the top is half the base width.
Different regions have made minor modifications to the general method of construction - sometimes because of limitations of building material available, but also to create a look that is distinct to that area. Whichever method is used to build a dyke, considerable skill is required. Selection of the correct stone for every position in the dyke makes an enormous difference to the lifetime of the finished product, and a skilled dyker will take time over the selection.
As with many older crafts, skilled dykers today are few in number. With the advent of modern wire fencing, fields can be fenced with much less time and expense using wire than using stone dykes. However the initial expense of building dykes is offset by their sturdiness and consequent long, low-maintenance lifetimes. As a result dykers remain in demand, as do the dykes themselves.
[edit] Notable dry stone walls
- Mourne Wall - 22 mile long wall in the Mourne Mountains location in County Down, Northern Ireland.
- Ottenby Nature Preserve, built by Karl X Gustave in mid 16th century, Öland, Sweden
[edit] Dry stone buildings
While the dry-stone technique is generally used for field enclosures, it was also used for buildings. The traditional turf-roofed Highland Black house was constructed using the double wall dry stone method. When buildings are constructed using this method, the middle of the wall is generally filled with earth or sand in order to eliminate draughts. During the Iron Age and perhaps earlier, the technique was also used to build fortifications such as the walls of Eketorp Castle (Oland, Sweden), Maiden Castle, Reeth and the rampart of the Long Scar Dyke. Many of the Dry-stone walls that exist today in Scotland can be dated to the 14th century or earlier when they were built to divide fields and retain livestock. Some extremely well built examples are found for example on the lands of Muchalls Castle.
In Swiss Italian region, dry stone buildings are also covered by the dry stone roofs, but this construction also needs wooden logs to support the roof span over the building space. Logs reduce the durability of the construction: it is common to find the buildings that have collapsed because the wooden parts have rotted away.(photo).
[edit] Dry stone bridges
Since at least the Middle Ages some bridges capable of carrying horse or carriage traffic have been constructed using drystone techniques. An example of a well preserved bridge of this type is a double arched limestone bridge in Alby, Sweden on the island of Oland (shown right).
[edit] Dry stone markings
In England and Switzerland, it is possible to find the dry stone constructions without any obvious functionality. The largest and oldest of them, like Stonehenge, are likely related to the ancient beliefs. However the smaller constructs may just be built as labels, marking the mountain pathes or boundaries of the owned land (some stand on the boundary between Italy and Switzerland, see photo).
[edit] Dry stone paths
In the mountain regions it is possible to find the dry stone paths. Apart the flat surfaces, they may also have the dry stone risers. Some are old; other are more recently build to prevent the erosion. In these days, the dry stone path is more difficut to build than other alternatives, but, once built, no maintenance is needed for a long time.
[edit] History
Some dry-stone wall constructions in North-West Europe have been dated back to the neolithic. Many cornish henges are believed to date from 4000BCE, although there appears to be little dating evidence. In County Mayo, Ireland, an entire field system made from dry-stone walls, since covered in peat, have been carbon-dated to 3800BCE.
[edit] References
- Murray-Wooley, Carolyn and Karl Raitz. Rock Fences of the Bluegrass, University Press of Kentucky. 1992.
- Francis Pryor, 'Britain BC', Harper Perennial. 2003.
[edit] See also
[edit] External links
- Dry Stone Walling Association of Canada
- Dry Stone Walls Association of Australia
- Dry Stone Walling Association of Great Britain
- The Guild of Cornish Hedgers
- British Trust for Conservation Volunteers skills page on dyking
- BTCV dry stone walling book
- Current Archaeology notes on Working Holidays repairing dry stone walls
- Dry Stone Conservancy, dedicated to preserving and promoting dry stone masonry.
