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.

LARGE-SCALE MODEL MAKING

SEPTEMBER 2014

The use of physical models by architects is well established, and can be seen throughout history as the natural partner to drawings for exhibiting a proposal of the building prior to construction. Within our practice, models are rarely produced as mere presentation pieces, but rather as tools for exploration. This role makes them less precious and complete, with the ability to change and adapt the design following the feedback that the model has initiated.

The type of models that I enjoy most are those of a larger scale, of 1:20 and above where you are able to get your head inside and truly appreciate the space. In addition to the final form of such models, much is learnt through the process of construction. Structure, surfaces and junctions are some of the issues that require resolution during the making of the model. Within our studio space, we have a large area dedicated to model making, which allows for building and display of sizeable pieces.

During our work on a new build private residence in Hampshire, we carried out much of the design work on the external envelope through the use of physical models. They were worked up in increasing scales including a 1:10 piece of the facade. In particular, we were considering the form of the heavy external piers, fascias and cornices against the lighter timber elements that sat within them. We made the model using a similar sequence to the proposed building construction. We put the more solid facade elements in place so that we could begin considering a number of different forms for the timber window framing that sat within. The glazing was again produced in a similar method to the full-scale building, with a timber-framed bay built separately prior to installation in to the existing facade. We fixed these delicately so that removal would be possible.

We worked on a number of iterations of the window form, adapting the frames and constructing new versions when modification was not possible. Each time, the model was left on display within the studio so that everyone in the practice could consider the alternative versions and provide feedback. Once we had a favoured form, we used the same model to illustrate the proposal to the clients for approval.

I believe that such iterative assessments and amendments would only have been possible through the use of a large-scale physical model. Building models is about constructing space, and many of the activities are similar in technique and execution as the construction of a real building. By carrying out these actions in miniature we may appreciate the building as a physical form and understand the three dimensional mass. Building of models is our primary opportunity to test and refine our building form, whilst experiencing and discovering an approximation of the processes that will be required to make it.

Alastair Crockett studied at the University of Bath, University College London and London Metropolitan University. Since joining Niall McLaughlin Architects in 2012 he has worked on the T1 building in King’s Cross; a private residence in Hampshire and the Nazrin Shah Building for Worcester College in Oxford.