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Great British Stone : Totternhoe Clunch

21 August 2015
The Totternhoe Clunch quarry today.

Clunch is just another name for chalk, which is not one the most durable of building stones. But Barry Hunt, as he continues his search for the great British building stones, believes Totternhoe Clunch deserves to be included. Here he explains why.

The White Cliffs of Dover. There have been songs sung about them, poems written to them, and even a movie made of them. The National Trust owns a five-mile stretch of them and is looking to secure more, believing them to have been a symbol of Britishness ever since Julius Caesar wrote about them in his Commentaries on the Gallic War.

William Shakespeare cemented their place in the British psyche by setting the climax of his play King Lear on them, with the blinded Earl of Gloucester wanting to throw himself from the top of them. And this natural fortress has long since provided a comfort blanket against potential invaders.

Most people are well aware the White Cliffs of Dover are chalk. But this is not the only place we find chalk. It is present along a vast swathe of the British coastline and underpins many southern hills, most notably the downlands.

Yet, in spite of there being so much of it and it often being easily accessible, chalk has been mostly passed over as a building stone. Understandably. It is an intrinsically weak material compared with most other building stones otherwise available.

Where it has been used, it is normally where it is found, because it has rarely been considered worthy of transporting any significant distance. It is far more amenable to crushing for use in cement production and, by that twist of fate, has become a stone widely used in construction.

Where chalk has been cut from the ground and used for building stone it has come to be known as ‘clunch’.

Clunch is a word that originally applied to chalk stone derived from pits in Cambridgeshire but has gradually come to be applied to any chalk stone.

Cambridgeshire clunch was mined from a seam of particularly hard chalk that ran all the way from the Chilterns of Buckinghamshire, through Bedfordshire and Hertfordshire and into Cambridgeshire.

The location of the stone was easily identified because a spring line formed where the stone occurred. The availability of clean water led to the establishment of small settlements, with the clunch being used as a building stone.

What is Totternhoe Stone?

Possibly the first use of chalk as a building stone was in the village of Totternhoe, in Bedfordshire.

Here there are the remains of a Roman villa built on the outskirts of what they called Durocobrivae, known today as Dunstable. The invading Roman legions set up a temporary fort there.

This was one of several temporary forts that were precursors to the building of Watling Street and the Icknield Way.

Totternhoe sits adjacent to a steep ridge of chalk that provided commanding views of the surrounding landscape, and it is here that the hardened seam of chalk reached its maximum thickness of around 5m.

After the Romans left Britain in the fifth century, quarrying essentially came to a halt until the invasion of the Normans in 1066, when it was kick-started again by the great church and castle building of the period. It is in the surviving remains of such buildings that we find Totternhoe stone today.

The geological story of Totternhoe stone is one of the inundation by the sea of much of southern England, beginning some 115million years ago during the Cretaceous Period .

Initially, sandy deposits now known as Greensand were formed but, due to global warming at that time, the sea deepened and eventually covered most of Britain and Europe. This resulted in a series of clays we now call the Gault, topped by another layer of Greensand.

It is estimated that 98million years ago the sea level was more than 20m higher than it is today and the conditions were such that there were huge blooms of plankton, the skeletal remains of which fell to the sea floor to form muds of lime (calcium carbonate).

These conditions continued for around 30million years, during which time hundreds of metres of lime mud were deposited. They eventually lithified into what we now know as chalk.

It is the fineness of the bulk planktonic fossil skeletons that were dominated by a microscopic creature known as a ‘coccolithophore’ that makes chalk such a dusty material. Because the sea level was so high there was little land erosion to introduce impurities, which is why chalk is so white compared with most other, less pure, limestones.

The Totternhoe stone was formed during the upper part of what is now called the Cenomanian Age, formerly referred to by geologists as the Grey Chalk Subgroup. The Cenomanian occurred between 98.5million and 93.5million years ago.

But the Totternhoe stone is a little different to the chalk that is generally passed over as a building stone.

During the formation of the chalk there were intervals when sedimentation slowed and more cementation occurred. In some instances the sea level dropped, allowing surrounding materials to erode so that a variety of pebbles and grits became included within the sediments.

Some of these materials included phosphates and the mineral glauconite (which typically has a green hue), shell, sharks teeth and bone fragments that make the stone of greater interest to fossil hunters and scientists.

Quarrying of Totternhoe Stone

In times past, the bed from which the Totternhoe stone is obtained was overlain by potentially up to 30m of overburden. This resulted in the majority of the stone being mined rather than extracted by open cast quarrying.

The last pit reportedly closed in 1914, when the mine galleries were sealed off because they were unstable.

This was yet another casualty of World War I and the changes in construction methods that followed.

Unfortunately, maps of the mines were lost during World War II and any survey of the mines would be too dangerous to carry out without them. It is known that the mines run at least 400m from exposed faces in some locations.

The story of the modern use of Totternhoe stone begins in the 1950s, when Woburn Abbey required major restoration works and the whole of one side was pulled down and the exposed ends re-built.

At that time, Totternhoe stone was not available and Doulting stone was used instead. However, it appears that a number of repairs were undertaken in what was believed to be Totternhoe stone but which may actually have been overburden chalk.

Stanley Clarke, father of Angus Clarke, the current owner of H G Clarke & Son, the company that quarries Totternhoe stone, revealed that in the early 1970s he was asked to cut stone for Woburn Abbey.

He began by supplying stone to replace badly failed masonry on the stable block. A newspaper was found that identified the stonework as being no more than 20 years old. Robin Russell, then the Marquess of Tavistock (later the 14th Duke of Bedford, whose family has owned Woburn Abbey since being given it by Edward VI in 1747) was advised that better quality stone should have been used and requested that the Totternhoe quarry be re-opened to supply it.

The quarry was visited by Stanley Clarke with the Woburn Abbey Clerk of Works, who saw that the roof of the quarry had collapsed some years previously, leaving large boulders of chalk. It was believed these boulders may have been used for the 1950s works instead of the true Totternhoe stone.

Having dug down into some of the tunnels, mini excavators were used to clear them and the best Totternhoe stone was exposed.

Approximately 200tonnes of stone were extracted for Woburn Abbey, the methods of quarrying being carefully developed to minimise the potential for damage to the stone as it was extracted. Careful drying was necessary to prevent the stone from distorting and cracking.

On completion of the work at Woburn Abbey, the quarry remained open with the assistance of the Marquess’ contacts.

Today, the stone is extracted under the auspices of the Wildlife Trust, which owns the land, now a site of special scientific interest (SSSI).

The Totternhoe stone comes in three distinct grades:

  • Firm grey sandy stone in beds totalling up to 2.7m thick
  • Hard brownish stone in two massive beds totalling up to 2.4m thick
  • Hard brownish stone in three beds with many phosphatic clasts at the base totalling up to 1.5m thick.

The current workings have a total bed height that can be up to 4m thick.

The Totternhoe stone deposit is underlain by a thin layer known locally as ‘fleck’, which sits on a layer of chalk marl. The top of the bed is marked by a thin black line, above which is grey chalk. These presence of these beds is fortunate as they allow the Totternhoe stone to be recognised easily.

The extraction process begins with the removal of over-burden. The stone is then cut using either hand or electric saws from beneath and behind and is allowed to fall or is slowly tipped on to the softer marl below.

Extraction takes place mainly during the spring and summer and it is believed that at the current rate of extraction there are supplies for at least the next 100 years. Block sizes vary from 0.5tonnes to several tonnes.

Properties and Use of

Totternhoe Stone

Normally I would provide a list of test results for a range of properties and discuss them in the context of how the stone performs in service, but test results available for Totternhoe stone are limited, so this is not possible.

The lack of test results is a consequence of the stone being used almost exclusively for repairs, which results in a relatively low output compared with most other British natural building stones.

Most customers simply want the stone for conservation purposes and do not feel the need to explore its properties.

This is contrary to the European Construction Products Regulation and the diktat that all natural stone used for construction purposes must have a range of tests undertaken and the results declared. The whys and wherefores of not having the stone tested is a discussion for another day.

The stone is considered to be fine for internal works, being extremely easy to carve. Externally, it is not expected to be as resistant to weathering as most other limestones, meaning that, ideally, it should not be used for the more exposed elements of a building nor be ornately carved.

Even in use as plain walling a high degree of weathering must be expected, especially if the stone is allowed to become saturated before frosts occur.

Chalk generally is particularly susceptible to deep laminar shaling under frost action and the Totternhoe is no exception, although it is more resistant than other chalks.

The water absorption is typically in the order of around 15%, while the saturation coefficient is relatively high – not a good combination of properties.

A density of around 1.9tonnes per cubic metre ought to put the stone in a category of its own – most limestones have densities of 2.1 up to 2.7. The stone also weathers by dissolution of the constituents at the outer surface by acidified rain, although this is of far less importance than the damage likely to be caused by frosts.

The high water absorption rate presents an almost unique problem with installation because of the stone’s high suction potential. Moisture can be rapidly drawn from mortars being used to set the stone, making them unworkable. It is reported that some stonemasons have coated hidden faces with linseed oil thinned with turpentine to reduce the suction while the stone was being fixed.

On completion of the construction there was sometimes an instruction that the face be treated with the same thinned linseed oil, which darkened the stone’s appearance. It is not known if this process had any effect, beneficial or otherwise, on long term durability. Without regular re-application, water might get in behind the treated surface, where it could be trapped and cause deeper problems.

Woburn Abbey remains the primary example of the use of Totternhoe stone, but there are many secular buildings in Bedfordshire and the surrounding counties where it can be seen. Eileen Roberts’ article ‘Totternhoe stone and Flint in Hertfordshire Churches’ (published in Medieval Archaeology, 1974, and freely available on the internet) is a pretty comprehensive read on the history of the subject.

Totternhoe stone is commonly used in combination with flint, a material formed within the chalk that might be considered its antithesis, being ferociously hard, impossible to cut, and present in small nodules only.

Records show that Totternhoe stone was used further afield – for the Palace of Westminster and Windsor Castle – during the 14th century. In the same period it was used in conjunction with flint to build the Dominican Priory at Kings Langley.

Totternhoe stone often exhibits zig-zag jointing, which is not perceived to be a problem until it is cut more thinly, when it can allow the joints to open up. It is for this reason that the stone should not be used for ashlar.

It is also important that the stone is used on bed, even though the beds may be difficult to see. Some stonemasons believed they could tell the bedding direction by the way in which water was absorbed at different faces.

Concluding Remarks

The stone industry has been through a considerable renaissance over the past 20 to 30 years. It has also now become subject to mandatory CE marking for construction products, and various codes of practice and Stone Federation guides have been published to help customers choose and use natural stone. A wide range of tests has been developed to help determine how best to use a stone. Just keeping up-to-date with the standards costs a small fortune, which I am convinced is a result of the monopoly operated by the British Standards Institution.

But there is a part of the stone industry that is either fighting against, or is blissfully unaware of these requirements – restoration.

Restoration is a difficult part of the stone industry that typically relies on truly dedicated people who love stone and do not seem to care about wealth creation.

Stone blocks are pulled out of the ground on an apparently ad hoc basis using relatively basic equipment often because there is insufficient money available to invest in anything else.

But with Totternhoe stone, simplicity appears to be the most appropriate course of action. There is no need to test the stone because those using it simply want to match existing material that has weathered away over the centuries.

Some may argue against putting something back that has previously not done too well, but failure is not necessarily always the stone’s fault and replacement offers a chance to set things right. And, of course, most restoration is driven by aesthetic requirements. The lightness of Totternhoe stone is difficult to match, making an alternative difficult to source.

Small quarries struggle to survive and those that somehow have managed to hang on in there in these increasingly demanding times deserve to be recognised. Totternhoe is a good example of a stone that survives on the basis of being part of the history of a particular area, one of the few survivors of the wealth of small quarries that once existed the length and breadth of Britain.

And it is because Totternhoe stone is a survivor, and chalk an icon of the British landscape, that it deserves to be considered a great British stone.

With thanks for the contributions of Angus Clarke, his late father, Stanley, and John Bysouth. Stanley kept a journal of the events leading to the re-opening of Totternhoe Quarry and the use of its stone, although it was discovered by Angus only after his father’s death. The events were independently corroborated by John Bysouth, who has been in the stone industry throughout a long and distinguished career. John also provided some of his own insights, as his father had worked on Woburn Abbey in the 1950s and he had worked there himself 20 years later. The histories knitted together to complete the bigger picture.
 

The Author: Barry Hunt

Barry Hunt is a chartered geologist, a surveyor and scientist. He has been awarded the designation of European Geologist and is a Corporate Building, Conservation and Specialist Surveyor. He is also a Member of the Chartered Institute of Building and a Fellow of the Royal Microscopical Society.
Barry has served on a number of professional committees, including the Technical Committee of Stone Federation Great Britain (SFGB), which provides advice on all stone construction issues. He is one of the authors of the SFGB team that has published codes of practice for the installation of stone floors and internal stone finishes.
Barry gained 14 years’ experience working as a consultant for two renowned civil engineering materials consultancies before, in 2001, establishing his own consultancy, IBIS, specialising in the investigation of construction materials.
The specialist knowledge and services provided by Barry have allowed him to be instrumental in the resolution of problems ranging from blast damaged claddings in London’s West End to advice on the quarrying and extraction of stone from abroad for import to the UK. Other areas of experience include the investigation of all types of building finishes, specialist advice on remedial treatments and the preparation of advice for potential and actual use in litigation or arbitration.
Having worked for consultancies that both undertook in-house laboratory investigation to UKAS requirements, Barry is also able to conduct or oversee a wide range of on-site and laboratory techniques and ensure they are carried out to traceable standards.
One speciality in all investigations is Barry’s hands-on approach. Being trained in industrial roped access (abseiling) allows him to get close to the problems with external building envelopes quickly, efficiently and cost-effectively.
Throughout his working life Barry has published findings from the many investigations he has undertaken. He has also authored chapters for two books on building stone and is currently engaged in other book projects in this field. His most important contribution is considered to be the chapter on the repair and maintenance of stone in the landmark Geological Society publication Stone.
Barry is also a regular contributor, covering the full spectrum of natural stone use, for Natural Stone Specialist magazine.    

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