Great British Stone : Clipsham

This is Clipsham stone on Bishop Edward King Chapel, shortlisted in the RIBA Stirling Award and Highly Commended in the Stone Awards last year.

Clipsham limestone is probably best known as a stone that has come to the rescue when other stones have not proved as resilient as anticipated, notably at the Houses of Parliament. But that is not the only reason Clipsham deserves to be included among the Great British Stones, says Barry Hunt.

Britain’s Houses of Parliament are some of the most widely recognised buildings in the world, so surely they must have been built using a great British stone?

The story is not that straightforward. Anston limestone from Yorkshire was originally carefully selected for the project but proved unsuitable for the highly acidic conditions created by all the sulphur emissions from factories and houses in ‘the Big Smoke’, as London was once known and is still sometimes called.

In the 1920s, Clipsham stone entered the story, being deemed a suitable match in colour to the Anston but better able to bear the brunt of the worst that London’s acidic fogs could throw at it.

Throughout the middle years of the 20th century the failed Anston limestone was gradually replaced by Clipsham. This established Clipsham’s reputation and it is now frequently the stone of choice when there has been a limestone failure that needs to be sorted out.

So you have to ask why Clipsham is not more frequently the stone of choice to begin with?

Clipsham limestone is produced from an area around the village of Clipsham in Rutland in the English Midlands. Somehow it has not achieved the widespread reputation of the Portland and Bath stones. But why not?

One reason, perhaps, is that there was no major city near enough to the source of the stone to be built of it. There is Peterborough, but that had a source of stone even closer to hand – Stamford.

There are Leicester and Nottingham, and maybe Cambridge, but all are served by their own local stone resources, while the surrounding area of Lincolnshire is blessed with many different stone resources.

Lacking a major centre to showcase Clipsham stone’s true talents deprived it of a significant marketing tool. Another drawback in the early days was that it is hard. It has a reputation for being the hardest of all the Lincolnshire limestones, which means it was more difficult to process than the surrounding resources until more recent times brought mechanical excavation, sawing and shaping.

Transport links – or the lack of them – probably did not help, either. There was the Great Northern Road (now the A1) but stone did not go far by road until well into the 20th century. The Victorian railways helped by bringing all kinds of building materials from the Midlands into Kings Cross and St Pancras, but Clipsham stone took a long time to emerge from the wilderness.

What is Clipsham Stone?

In many ways Clipsham stone is similar to both Portland and Bath stones. They are all oolitic limestones formed during the Jurassic age. In other ways it is different.

Clipsham comes from a sequence of rocks known as the Lincolnshire Limestone Formation, which is part of a larger sequence referred to as the Inferior Oolite Series.

These rocks formed in shallow but energetic sub-tropical seas 174-168million years ago.

The constituent grains were precipitated out of solution to form ooliths, which are small, egg-shaped (ovoid) grains that form by gradually building up layers, much the way hailstones do.

The size of the grains is dictated by the energy of the prevailing currents of the seas the stone is formed in, as is the presence or otherwise of finer matrix materials.

The ooid formation process was described in the earlier article in this series on Portland stone (see NSS May 2014).

In the sea in which the Clipsham stone was formed there was a strong current that has left the stone with a relatively coarse grain size and minimal matrix. Later, calcite formed between the grains to ‘glue’ them together and create the solid stone.

Closely related rocks (essentially from the same rock sequence) include the Greetham, Ketton and Stamford stones, all well known in their own right and direct competitors of Clipsham stone.

With similar stones all within a relatively small region there has almost inevitably been an argument over what should legitimately be considered Clipsham stone. This is not a problem unique to this area and I have previously explained the problems of stone classification, most notably in my article on York Stone (see NSS July/August issue 2014), where the stone has no actual ties to the City of York. The argument about Clipsham stone, on the other hand, has been very much about the location and proximity of the resources to the village.

Historically, Clipsham is reported to have been quarried since Roman times, when it was used to build local villas. After that, Big Pits Quarry is known to have started operating in the 11th or 12th century and was used sporadically. Two faces were worked, one being known as Big Pits, the other as Old Quarry.

Holywell Quarry also operated in medieval times but was not used again for centuries. Holywell Quarry yielded a stone that achieved sufficient fame for it to be shipped to Windsor castle between 1363 and 1368, which is noted in the records of the English Exchequer, or Pipe Rolls.

Big Pits quarry re-opened in the early 20th century along with Longwells and Medwells quarries, the latter backing on to the then disused Holywell quarry.

Medwells was also called the New Quarry and was the only quarry operating in the area from the 1950s onwards until the Old Clipsham quarry re-opened.

Meanwhile, the Medwells quarry essentially moved operations into the old Holywell quarry, and these are the two Clipsham quarries currently operating.

Types of Clipsham Stone

Unlike Portland (with its Basebed, Whitbed and Roach), or Purbeck (with its Burr, Thornback, Whetson, Grub, Marble and more) and many other stones, there are not really distinctly different beds of Clipsham stone. Instead the variations are subtler between beds.

The stone presently quarried is described as exhibiting a buff colour that is relatively consistent. Occasionally there are pinkish tints that change to buff over time.

Some locations are found to exhibit what is described as a ‘blue heart’, which is actually less geologically weathered material that is typically much harder than the buff stone.

Potentially, the blue-hearted materials, although appearing stronger and performing better in tests, are actually less stable once exposed to the atmosphere. In total there is about 5m of workable beds.

Variations in the stone occur due to features known locally as ‘swallows’, which appear to be the result of small depressions in the original seascape so that thicker stone units are formed. These are the source of the finest stones.

Blocks vary in size from 0.5tonnes to 9tonnes and the greatest bed height reaches 800mm. A variety of local names have been used for different visual grades of the stone based on colour and the finest stone is considered to be the lightest and most consistent in colour.

Properties of Clipsham Stone

Test results obtained for Clipsham stone are for ‘standard block’ stone and ‘hard white’ stone.

The results suggest that the stone is borderline between what may be regarded as low to medium density limestone.

What is interesting about the results is that the hard white stone exhibits twice the compressive strength of the standard block but performs far worse under the action of salts during the salt crystallisation test.

The saturation coefficient of the hard white is significantly higher than that of the block stone, suggesting its apparent lack of microporosity is being exploited and in the long term could indicate lower resistance to frost damage. This is yet another example of where good strength results do not necessarily imply best performance.

It is possible that Clipsham stone shares some of the special properties of Portland stone, notably a granular oolitic structure and a low grain connection that allows water to drain from the stone relatively quickly.

The reduction of retained water means that the potential for any remaining water to freeze and cause damage is reduced.

The presence of significant microporosity also provides a buffer to the freezing effects, reducing the internal pressures that could otherwise build up.

However, Clipsham stone will be damaged by frost if it is used in a situation where it cannot drain.

Clipsham stone tends to weather by slow dissolution of the constituents at the outer surface. Dirt eventually builds up and sticks to the surface, darkening the colour, although it is a simple matter to remove this thin veneer to bring the original stone back to life again.

The dissolution rate of the stone has not been determined so far, but it appears likely to be just a few millimetres every hundred years.

The stone can also suffer the discolouration that afflicts most limestones when placed in contact with grey Portland cements, so white cements and lime should always be used with it.

Use of Clipsham Stone

The principal use of Clipsham stone is for traditional masonry, typically hand-set ashlar, given the limitations on bed heights and block sizes.

It is a perfect material for this job due to its consistency and ease of use.

This is why it was selected as the stone for the replacement of the Anston at the Houses of Parliament and it is this role of a replacement stone for others that have suffered failure that seems to have dominated its use, although some would question the wisdom of using a more resilient stone to repair weathered stone as it could lead to accelerated decay in the surrounding original material. That is a subject for debate at another time.

Notable buildings where Clipsham has been used as a replacement stone apart from the Houses of Parliament include York Minster and a number of college buildings in Oxford.

Clipsham stone is readily used for copings, cornices, stringers and occasionally for monumental work and statuary.

John Bysouth, a doyen of the stone industry who ran his own highly respected stonemasonry company in London for many years and is a former President of Stone Federation Great Britain, recollects a tale told to him by his father, from whom John inherited the business, when he used to visit the Medwells quarry to select stone.

A man from the Ministry used to arrive and select stone for the repairs to the Houses of Parliament, marking up the stones and having them put to one side. When quoting for work at the Houses of Parliament, masonry companies were informed that the block would be made available from the Ministry stock at the quarry and you were told what price you had to pay.

The system was in place when John joined his father’s company in 1958 but was eventually discontinued as the amount of necessary repairs dwindled.

Across the country in Oxford the poor performance of the local Headington stone had left Victorian Oxford in a crisis of dilapidation. The Architect Thomas Graham Jackson cemented his place in Oxford architectural history by being the first to use Clipsham stone there, for the Examination Schools (1876-8). He employed a Jacobean style never before seen in Oxford.

Jackson ignored Oxford traditions to bring a more modern style of construction to the City and in doing so launched Clipsham on to the landscape. Jackson then continued to use it in both new constructions and for bringing new life to existing buildings.

The extensive use of Clipsham stone in Oxford feels like a statement of intent to Cambridge: if you are not going to use your best local stone, then we will.

And so, slowly but surely, Oxford has become a city of Clipsham stone and as such is ready to face the centuries ahead.

Of course, Oxford is not famous for its Clipsham stone, that is just incidental to the architecture and the University. But it has its moments and gained significant recognition last year as the material used in innovative ways for the construction of the façades of the Bishop Edward King Chapel, which was short-listed in the architectural Stirling Prize and recognised in the 2014 Natural Stone Awards.

Niall McLaughlin Architects’ Bishop Edward King Chapel for Ripon Theological College in Cuddesdon, Oxfordshire, was described by the Guardian newspaper as “… the kind of building every architect dreams of making. A jewel-like distillation of ideas about materials, light and space, it is beautifully built in hand-cut Clipsham limestone…” (Oliver Wainwright, the Guardian, 18 July 2013).

The stone came from Clipsham Quarry Company’s New Quarry and was worked and supplied by Stamford Stone Company. It included 14,480 pieces of hand cut dog tooth walling along with radial ashlar, plinth, coping and treasury windows.

This is just one particularly notable example of how the stone continues to be used for new build as well as for renovation.

More recently, the interiors market has also started to embrace Clipsham stone, and Clipsham Stone Company has joined forces with another local business to supply a range of lamp stands, placemats and other domestic items not widely associated with limestones.

Concluding Remarks

Clipsham stone deserves greater recognition than it has historically received.

It is a direct competitor to Portland stone in performance and has been mostly used as a universal panacea to replace other limestones that have not stood the test of time.

I stated at the start of this article that Clipsham stone had not benefitted from a local major town or city using the stone to showcase it, and although Oxford has seen fit to step into this role, there is still a long way to go.

Nevertheless, Clipsham stone has managed to overcome the adversity of a difficult location by virtue of its undoubted quality – a quality recognised in particular by some of those saving significant contributions to the country’s built heritage.

And despite being a relative latecomer (or late returner, perhaps) to the party, Clipsham certainly deserves a place in the pantheon of the greatest of British stones.


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.