An Arch Never Sleeps
by Patrick McAfee
Patrick McAfee of the Building Limes Forum Ireland (BLFI) in conjunction with Drimnagh Castle, Dublin ran a Heritage Week event over the course of three mornings in August called ‘An Arch Never Sleeps’. The aim was to introduce the general public to the wonderful world of arches having a brief look at their history and then to experience in practice how they were built.
Facing each days audience were the many arch shapes of Drimnagh Castle itself. As one member of the audience said ‘It is only when you really look that you see arches everywhere’, this is equally true of our cities, towns and villages.
For the audience to assist in the building process then the voussoirs (individual stones that make up an arch) had to be either small scale or full size of a lightweight material. Light weight insulation type blocks were selected and cut to shape using traditional stonecutting tools before the workshop commenced.
Each day a young volunteer/s from the audience came forward to assist with building the semi circular and gothic arches. When the final stone of each arch (keystone) was laid and the timber centre removed the arch came alive, it was as if suddenly something magic had occurred and it had, not only in the eyes of the young helpers but also amongst the adults in the audience. Something taken for granted and not thought about until now became something to think and marvel about. The response from the audience was always the same, spontaneous applause, with the young helper/s taking a bow.
Since Roman times lime mortar was very much a part of arch building and is one reason why so many arches still survive. Why? because lime allows movement; the arch barrel of the bridge moves with traffic and expands and contracts with changes in temperature but these movements mostly occur in the lime mortar joints and not in the stones themselves otherwise they would crack and fail. A segmental arch was built in brick and lime mortar. This is another common arch but it often hides away where we cannot see it behind plasters and renders relieving or taking the weight that would otherwise be applied to the timber lintel underneath.
The expression ‘an arch never sleeps’ is attributed to the Arab world and beautifully sums up what an arch does, it safely transfers its own weight and applied forces down its sides, it is therefore ‘alive’ dynamic, relentlessly working.
If the world was abandoned for a millennium I doubt we would find many surviving examples of modern buildings, the steel would have rusted and destroyed the concrete and anyway very few buildings today are designed to last much more than half a century. Amongst the thick undergrowth stone and lime mortar structures would be found that are historic even in today’s terms and a prominent feature of those structures would be the arch, still working, dutiful, tired but never once in a thousand years having fallen asleep.
The Building Limes Forum Ireland is a voluntary organisation that seeks to encourage expertise and understanding of the use of lime in building www.buildinglimesforumireland.com