7 Building Stone Walls
The relationship between stone and the mortar is basic: every ingredient that makes mortar was once stone. Balance and compatibility are the qualities needed when adjusting the mortar to the hardness of the stones being used. Not all stone constructions uses mortar. Some extraordinary walls are built with no mortar at all. The famous Inca walls at Sacsayhuaman and Machu Picchu are made with shaped interlocking stones, carefully trimmed to snuggle up to each other. Their design is credited with resisting centuries of earthquakes. Not everyone can build such walls. Tetsuroh Tanabe in Japan is one of the few contemporary masons building similar walls. A more extreme, and more critical, version of the same principle is used in the interlocking bases of lighthouses on the westcoast of Scotland. Granite blocks are carved so that they can interlock both vertically and horizontally and are thus able to resist the normal sea and the occasional storm with 90-foot waves.
Instead of shaping each stone to interlock, many walls are built using only available stone of random shapes. This seemingly simple process requires more skill than many other stone working processes. It is also one of the few human skills that has been practiced nearly unchanged since prehistory.
Mortar-free constructions anywhere in the world follow the same building. The structure of support in a dry stone wall is one of invisible efficiency. No stone is independent in a stone wall, each stone is held in place by a network of neighbouring stones and in turn is held in place by others. When using found stone the skilled waller learns to quickly judge the weight and shape of eachstone. This is clearly a developed skill based on assessment and response. Although somewhat less than interlocking shaped stone constructions, these random stonewalls also have an elasticity that walls made with mortar do not have. A successful dry stone wall can last for centuries without maintenance and yet it is not always possible to see in a new wall whether that particular wall will be long-lived. A single point where the balance is not perfect, or where water and ice may weaken a link, can make the entire wall vulnerable.
Every type of stone construction has its own character, almost like a social construction. Most stones in a cathedral, for instance, will have roughly the same geological age. They will have come either from the same quarry, or the blocks used will have been matched according to similar qualities. A dry wall, in contrast, is a pluralist structure. Stones will have come from widely different time periods. Glacial rocks may have brought stones from great distances. Diverse age and geography come together for a single purpose. As a wall they must all work together.
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