REIGATE STONE RECORDING AND RESEARCH PROJECT
Historic Royal Palaces Surveyor of the Fabric's Department
Reigate stone occurs in the upper greensand beds at the foot of the North Downs in Surrey. The outcrop runs from Godstone in the east to Brockham in the west, centering on the town of Reigate. It is one of the few buildings stones to be found in south east England, although its use as a building stone had ended by 1939.
Reigate stone was used extensively in high status buildings in London in the medieval period. Significant areas of Reigate stone survive at both the Tower of London and Hampton Court Palace, although the condition of the stone has been giving cause for concern in recent years.
The research project was instigated by Historic Royal Palaces in 1996 to survey and record the extent and condition of the surviving Reigate stone in the Palaces, and to further our understanding of the nature of the stone and of conservation techniques.
Given the vulnerability of Reigate stone, and its diminishing extent, recording was given high priority in the project. The surviving Reigate stone at Hampton Court Palace was recorded in early 1997 using stereo photography. Selected areas of Reigate stone were also photographed at the Tower of London in early 1998. The photography was carried out by the Downland Partnership. Locations of stone were also marked on CAD plans.
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The condition of Reigate stone The variability of decay rates in Reigate stone is particularly noticeable. Some Medieval and Tudor stonework is still intact, while other areas are in a decayed state with decisions conserving their conservation or replacement imminent. Adjacent stones can display markedly different rates of decay. At the present time there is no explanation as to why adjacent stones decay at different rates. The Reigate stone in the upper chamber Wakefield Tower at H.M. Tower of London is giving particular cause for concern. Here the variability in the decay of adjacent stones is not seen. Instead an entire pier is eroding at a uniform rate. To assist in understanding the causes of the decay here, a GIS project has been set up in collaboration with the University of Portsmouth. (See section on GIS below.) |
At the present time, the HRP uses the lime method in the conservation of Reigate stone. At the Tower of London a series of conservation jobs by Nimbus Conservation using the lime method on Reigate stone carried out in the 1980's and early 1990's were successful technically and aesthetically, although the technique does need to be repeated in exterior locations after ten to twelve years.
Elsewhere in London, silica based consolidants have been used in the conservation of Reigate stone. The Annunciation Door at the Chapter House of Westminster Abbey was conserved using silica based consolidants in the 1970's, seemingly with success. (See Taylor et al below.) Brethane trials were carried out in the Wakefield Tower in the 1970's, although it has not been possible to trace records of this to date.
The HRP's policy is to use Chilmark stone where Reigate stone needs to be replaced. This was the case with repairs carried out to the south facade of the White Tower in early 1998, which is the first occasion on which the HRP has found it necessary to replace Reigate stone. Previously German "grun" sandstone has also been used, for instance for dressings to the exterior of the Cradle Tower, carried out by Nimbus, circa 1990.
Elsewhere in the London area, limestones from northern France have been used to replace Reigate stone. Lepine stone has been used to replace Reigate stone at St. Katharine's Church, Mershtham. At the present time (early 2000) Richemont Bleu stone is being used to replace decayed Reigate stone at St. Margaret's Church, Chipstead.
A group from the HRP were taken down the abandoned Reigate stone mines at Merstham in February 1998, guided by Paul Sowan and Vince Allkins of the Wealden Cave and Mine Society. The former working face can be seen and three distinct beds of stone can be made out. However it is not known which of these beds provided the best building stone, a factor which may explain the variation in decay rates seen in buildings.
The impression gained from the visit was that the possibility of reopening any of the mines in order to extract new stone for use in repair work is unlikely. There is however some scope for the used of salvaged stone; a practice that has a long history. Reigate stone from Merton Abbey was used to build Nonsuch Palace in the 1530's, and was reused elsewhere when Nonsuch was demolished in the seventeenth century.
More recently Reigate stone from Merton Abbey, extracted as a consequence of a road building project in the early 1990's, was salvaged for use in the repair of the grotto at Carshalton House. Banstead and Reigate District Council keep a small store of Reigate stone, salvaged from agricultural buildings that have been demolished, for use in the repair of listed buildings.
In January 1998 Phillip Hartley and Jo Thwaites of HRP, and Keith Garner, the project co-ordinator, visited the the Bavarian State Conservation Office in Munich. The visit was at the invitation of Professor Rolf Snethlage. The purpose of the visit was to compare German and British practice in the conservation of masonry monuments. It was clear from the visit that significant differences of approach exist; particularly with regard to the use of chemical consolidants.
The visit to Munich also highlighted the development "decay mapping" of masonry monuments. In Germany, the technique has been pioneered by Professor Berndt Fitzner of Aachen Technical University (RWTH), although there are other systems. In March 1999, Phillip Hartley and Keith Garner, accompanied by Rob Inkpen and Dominic Fontana of Portsmouth University, visited Professor Fitzner and colleagues in Aachen.
The interim report of March 1998 set out a number of conclusions and recommendations for further investigation. Principal among these was the recommendation to proceed with geological sampling and analysis of Reigate stone in order to find out more of the detailed composition of the stone and its variability both along the outcrop and across the bed. This was considered to be a prerequisite for trials of alternative conservation treatments would be set up at locations around the Palaces subsequently.
It was also felt that the use of GIS and decay mapping were areas that should be explored further, as these appear to provide a greater understanding of the condition of masonry monuments before decisions on stone conservation and replacement are taken.
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Stone samples were taken from three abandoned mines in Merstham in April 1999. The mines were selected as they are among the easiest to access along the outcrop. A series of 50 mm dia. cores, approximately 150 mm deep, were taken at approx. 200 mm centres across the abandoned working face. Thin sections have been made from the samples and some preliminary SEM work has been carried out by Robin Sanderson. Other tests on the samples will be proceeding in the early part of 2000, with a view to having the findings published in a learned journal. |
Geographic Information Systems (GIS)
A GIS exercise has been set up in collaboration with the Geography Department of the University of Portsmouth, in order to form a clearer understanding of the processes influencing the decay of Reigate stone in the upper chamber of the Wakefield Tower at the Tower of London. In part this process is understood to be arising from heavy salt contamination (Price 1993) but the current investigation is seeking to relate the rate of decay to other variable such as temperature, relative humidity and visitor numbers.
As part of the GIS exercise, a three dimensional model of the Upper Chamber of the Wakefield Tower is being assembled by Keith Garner.
A trial decay mapping exercise is also underway at H.M. Tower of London at the present time, looking at the south facade of the Byward Tower. This exercise is being carried out in collaboration with the Geography Department at Portsmouth University.
Project sponsor:
Historic Royal Palaces,
Surveyor of the Fabric’s Department
Barrack Block,
Hampton Court Palace,
Surrey KT8 9AU
Jo Thwaites Project surveyor Tel 0208 781 9854
Richard Roberts Clerk of Works Tel 0208 781 9828
Consultant geologist:
Robin Sanderson FGS,
71 Acacia Grove,
New Malden,
Surrey KT3 3BU
Tel 0208 949 4236
Fax 0870 131 9308
mailto:robin.sanderson@btinternet.com
Project co-ordinator:
Keith Garner Architect,
70 Ethelburga Tower,
Rosenau Road,
London SW11 4AB
Tel 0207 585 0421
Fax 0207 801 9591
mailto:keithwgarner@btinternet.com
Special advisor on the archaeology of the Reigate stone mines
Paul Sowan FGS,
Subterranea Britannica,
254 Pampisford Road,
South Croydon,
Surrey CR2 6AD
Tel 0208 681 6293
Geomorphology and GIS
University of Portsmouth,
Department of Geography,
Buckingham Building,
Lion Terrace,
Portsmouth PO1 3HE
Tel 01705 842477
Fax 01705 842512
Rob Inkpen
Dominic Fontana
Peter Collier
Further reading about Reigate stone and its conservation
Published
Lockwood, Steve, "Reigate Stone: Geology, Use and Repair", Structural Survey, Vol.12 No.3, pp73-88
Owen, H.G., "The stratigraphy of the Gault and Upper Greensand of the Weald", in Proceedings of the Geologists' Association, Vol.86 part 4 1975
Price, Clifford, "Preventative conservation of salt-contaminated masonry in the Wakefield Tower, HM Tower of London", Institute of Archaeology Bulletin, No.30, 1993
Sowan, Paul, "Firestone and hearthstone mines in the Upper Greensand of East Surrey", in Proceedings of the Geologists' Association, Vol.86 part 4 1975
Taylor, K., Gradwell, C., & McGrath, T., "The cleaning and consolidation of the stonework to the Annunciation Door, Chapter House, Westminster Abbey", in Ashurt, J., & Dimes, F., Conservation of Building and Decorative Stones, Butterworth-Heineman, 1992
"Stone quarries, lime burning, Fullers' Earth etc", Victoria County History; Surrey, Vol.3 pp277-281
Unpublished
Domingo, Tina, "Paragenesis and Provenance of Archaeological Material, MSc Thesis, Queen Mary & Westfield College, University of London 1992.
Garner, Keith; Reigate stone recording and research, Interim Report; Historic Royal Palaces, Surveyor of the Fabric's Department; March 1998. Contains a more comprehensive list of references
Lockwood, Steve, Reigate Stone, Dissertation written for the College of Estate Management diploma in building conservation, 1994
Sanderson, R.W, "Reigate Stone; Notes on its occurence, charachter and use", February 1998. Included in the above report.
Historic Royal Palaces
Keith Garner Architect
Masonry Conservation Research Group
Wealden Cave & Mine Society