A Stone Glossary

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.

THE FURTHEST FROM THE FLOOR

NOVEMBER 2014

Imagine a room without a roof, where the sky can be seen and the seasons read. This room holds the capacity to frame dazzling colour and scaleless formation, silent motion and subtle evolution.

What if a roof challenged these things, and set out to generate a drama quite of its own?

Often we witness the world at eye-level alone. Much of our urban landscape positively encourages us to do so. Yet it is sad if, on the occasion we raise our eyes to the ceiling, we are not enamoured with what we find. It is often height that offers the best opportunity for expression. With height comes volume and the potential to present the greatest manifestation of depth and structure.

Our practice explores the roof and the complexity of a soffit as an ongoing theme. The notion of the exposed rafters in a barn has influenced the design of the soffit in our gallery at Auckland Castle. We are developing an array of rafters that create density yet delicacy in their mass when tightly multiplied. Though the roof is low, its lowest point occurs just higher than your fingertips, creating a definitive datum between the world of rafters and the world of exhibitions. This effect is further enhanced by the muted nature of the walls to increase the feeling of overhead awareness.

As contrast to this, your gaze is directed by the vertical piers that surround you as you move through Bishop Edward King Chapel in Oxford. Slowly they rise, higher and higher, until they meet the ceiling, at which point orientation is adjusted and the piers fuse with the weave of rafters. It is pleasurable to witness something simple become something complicated. Height offers the opportunity for elements in the space to take you on a journey. They “pick you up” at eye-level and carry you up to the roof, where often the brightest or darkest environments exist.

The requirement to defend from rain leaves the roof little choice but to protect, as efficiently and simply as possible, granting the interior more freedom for expression. And why not, when you consider where most building users will stand? However, as our towns and cities become denser, the roof, as seen from its surroundings, becomes an increasingly important issue to address.

The two examples I have given construct varying degrees of interest, leading me to suggest that it is possible for a roof to respond to that drama in the sky with a drama of its very own.

Katherine received a BSc Degree from the Bartlett in 2008. In 2007, she was awarded The Henry Herbert Bartlett Travel Scholarship and the UCL Expeditions & Travel Grant to conduct a construction project in Kampala. She joined Niall McLaughlin Architects in 2012 and has worked on London Academy of Music and Dramatic Art, St Cross College in Oxford, the T1 Argent Building in London and Jesus College in Cambridge.