Níall McLaughlin
Architects

A STONE GLOSSARY

MAY 2018

William ‘Strata’ Smith’s 1815 Geological Map, the first nationwide geological map ever published.

We are in the process of choosing the stone to be used for a new building in Cambridge. It has been an apparently exhaustive journey through marbles and limestones from the UK, Europe and beyond. We amass endless samples, and talk in detail to quarrymen, masons and engineers about bed heights, weathering, and reliability of supply, as well as the inevitable costs to quarry the stone, cut it to shape, and fix it together to form a building. One of the most fascinating elements of this process are the specialist terms used to describe building stones and their properties. Below is a list of a few favourite words, ordered to explain the material properties that have so far governed our explorations for this new project.

The Clipsham Quarry at Rutland in Lincolnshire. Clipsham Stone occurs in the Inferior Oolite of the Jurassic System, where it was laid down between 174 and 163 million years ago. Clipsham is a popular building limestone with a characteristic golden colour. We have recently worked with it at Bishop Edward King Chapel in Cuddesdon and the Sultan Nazrin Shah Centre in Oxford.

Bedding plane

Many building stones, including all limestones, are sedimentary rocks, formed by the gradual settlement and compression of underwater sediment over millions of years. The directional way in which they were formed governs their properties and how they can be used as building stones. Most UK limestones must be used ‘naturally bedded’, i.e. orientated in the building in the same way that they were formed in the ground. This means the height of the blocks is limited to the depth of the bed, rarely more than 1m in the UK. ‘Face-bedding’, when blocks are laid so their bedding planes are parallel with the vertical face of the block, can lead to rapid weathering and crumbling.

Metamorphic

A stone that began as another type of rock and changed as a result of exposure to heat and pressure over geological time. Marble was originally limestone, and is chemically identical to it. However, the metamorphic processes changed its physical properties so that it does not have bedding planes, and can be cut and orientated in any direction. This makes it ideal if tall blocks are required.

Precipitation

The chemical process by which Travertine is formed, usually when geothermally heated water is exposed to the air, causing it to degas and carbonate minerals to precipitate out from the water. Although a type of limestone, its distinctive formation means it also doesn’t have bedding planes and is workable in much longer, thinner pieces than sedimentary stones.

Oolitic

A type of limestone made from an amalgamation of individual grains called ooliths. An oolith is a tiny carbonate particle surrounded by concentric layers of calcium carbonate, which were deposited as the ooliths were rolled around on the bed of the clear shallow sea in which the stone was formed. This gives the stone an even structure so it can be cut or sculpted in any direction, a characteristic which makes oolitic stones ‘freestones’. Portland Stone is an oolitic limestone used extensively in London’s historic buildings, perhaps most famously in churches by Cristopher Wren and Nicholas Hawksmoor, including St Paul’s Cathedral and Christ Church Spitalfields.

CRAFTLINES

AUGUST 2015

My grandfather has worn many hats; soldier, civil servant, father of seven, husband, and winner of a county final in hurling (the achievement of which he is potentially most proud). He is fluent in Irish and recalls event and dates from 50 years ago with a staggering accuracy. Yet the residing image of him from my childhood is as a craftsman – in the garage next to his house in Dublin, whittling and sanding a piece of ash to form a hurley, sizing it precisely for the user, wrapping the handle to create the perfect hold. I remember sitting, playing surreptitiously with a clamp, watching this in awe: the creation of the perfect instrument from a piece of timber; a skill honed through practice and an unfailing attention to detail. I marvelled at the assurance of it all, the promise in his hands.

It would be satisfyingly simple to attribute my choice of career to these moments – to claim there was an epiphany in watching him, a sudden realisation that I wanted to be an architect, to create. In reality, however, the path was not so linear; instead the conviction that I wanted to become an architect embedded itself in my consciousness slowly, over time. The memory of him working in his garage was one I didn’t return to often, and like any story we fail to repeatedly tell ourselves, it languished, dormant, in the recesses of my mind.

I recently went to site at Jesus College, Cambridge, where we are working on a project that is part new build, part refurbishment. An aspect of the refurbishment involves the adaptation of eight bookcases in the magnificent former library into wall panelling. The existing bookcases are a dark stained timber, designed by Maurice Webb in the 1920s and wonderfully crafted by a masterful hand. Reworking these without compromising their beauty would be a challenge for any craftsman.

On seeing the work the joiner had done, I realised there was no cause for worry – it had been executed with confident, competent hands. In that moment, the memory of my grandfather in his garage came back to me in glorious Technicolor; and I felt a familiar thrill at the embodied potential of the right material in the hands of a craftsman, with promise in his hands.