I refer to the article in the January issue of Natural Stone Specialist which reports that Maurice Rogers has suggested that as the proposed high speed train route passes through areas which have, in the past, supplied sources of building stone, the development could be used as a source of building materials, providing “adequate stocks of stone to last for a hundred years”.
Unfortunately, there are a number of factors which make the suggestion unlikely to be practical. Furthermore, such a concept could be a potential problem to those struggling to secure sources of our important historic stones.
Although building stones tend to be referred to as coming from a certain geological horizon, it is often not appreciated that this does not mean that all that particular horizon will yield stone suitable for building.
The location of building stone for restoration use can be extremely complex, as a range of factors has to be considered. These are discussed in outline in English Heritage’s Technical Advice Note on Identifying and Sourcing Stone for Historic Building Repair, as noted by Mr Rogers in the article on Baddesley Clinton in Natural Stone Specialist July 2011.
I agree that the suggested high speed train route passes over strata, such as the Triassic Arden sandstone, from which building stones have been obtained in the past. However, the strata which is suitable for use as a building material is extremely limited. Even that stone which is potentially suitable, may be found to be unsuitable due to its petrography, bed height or form, jointing or depth of natural weathering.
This last point is important since although an horizon may have yielded building stone at the surface, at depth its petrography can change sufficiently to make it unsuitable as a replacement material. Stone extracted from railway tunnels could well be completely different to the same strata at the surface.
Where an horizon from which building stone has been extracted extends over any distance, the petrographic changes can be very important. For example, the Arden sandstone used at Baddesley Clinton occurs in at least three different forms, none of which are inter-changeable for conservation use.
As building stone advisor to English Heritage, as well as being tasked with locating acceptable stone for conservation work for the National Trust, many cathedrals throughout the UK, major stately homes, as well as hundreds of parish churches and other historic stone buildings, I am only too aware of the complexity of finding suitable materials for repairs to historic stone buildings. If it were only as simple as heading for the nearest major construction site in the relevant geological strata!
There are two further points which are pertinent to the concept of using stone from excavations along the route of the proposed train route. The first of these is the method of stone extraction. The aim of the contractors will obviously be to excavate as quickly as possible. This involves the use of equipment which will break down the stone as efficiently as possible, in order that it can be removed at minimal cost from the advancing face. In the tunnels in the relatively soft strata along the route, this will involve the use of tunnel boring equipment, the broken stone probably being removed by conveyor. Furthermore, since fill is expensive, a system of cut and fill will undoubtably be used, stone from cuttings and tunnels being used to build embankments. There will certainly be little chance of slowing down the development while blocks of stone are carefully removed using completely different equipment. Furthermore, if hard stone is encountered, blasting would be employed to comminute and remove the material. No stone which has been subjected to blasting should ever be used as a building material, especially for conservation use.
The second point arises from the suggestion that ‘stocks’ of stone could be available for a hundred years. Building stone can only be stored in the ground, or at least in a frost-free environment where a high humidity stops it from drying out. This is the reason why, when a building stone quarry ceases extraction (for example over winter) the exposed stone is often covered with overburden. The logistics of locating storage areas which can conserve extracted stone in an in situ condition would result in extremely expensive stone.
I noted above I consider the suggestion that stone for conservation use could be obtained from the route of HS2 could also create other potential problems for those involved in the extraction of stone for conservation projects.
Those of us involved in such work are only too aware of the problems encountered when attempting to obtain planning consent, even for small quantities of stone.
Sadly, the conservation of our historic built environment appears to be extremely low on the political agenda, especially compared with ‘biodiversity’, also known as gardening, that even the smallest hedgerow or tiniest pond can take precedence over the building stone upon which it is situated, or the historic building for which it is required.
The cost of fulfilling all the requirements – from ecological studies to flood-risk assessments – is astronomical in the context of conservation budgets. To potentially mislead those responsible for planning by suggesting that we may not need to open up small extraction sites for conservation stone because HS2 and other construction projects could provide all the stone we need, could amount to sounding the death knell for many of our historic stone buildings and monuments. We just do not have the financial resources to deal with yet another obstacle within the planning process.
Certainly, if a stone which is required for ongoing conservation work is encountered during a construction project – be that HS2 or any other ground engineering work – the viability of extracting that stone should always be considered.
Planners and others involved in such work should be aware of the need to recover such conservation materials, just as they are aware of having archaeological features investigated when they are encountered and act accordingly. However, the suggestion that significant quantities of scarce conservation materials could be found and stored, could well make the job of those responsible for locating and extracting very specific building stones, which are often required if the original fabric of a building is not to be further damaged, even harder.
Dr David Jefferson, B.Sc.(Hons), Ph.D., C.Eng., C.Sci., F.G.S., F.I.Q., M.I.M.M.M.
Director, Jefferson Consulting Ltd
Geology & Petrography in Conservation, Restoration & Archaeology
The Old Armoury, Crown Business Park, Old Dalby, Melton Mowbray, Leicestershire LE14 3NQ.