Mapping the limestone decay and decay processes on the external limestone of Chichester Cathedral, a structure stemming from the period circa 1076-1090
Chichester Cathedral, the construction of which commenced between 1076-
90, within the rural setting of Sussex, is composed of an eclectic mix of
limestones and some sandstones, which have undergone continued
replacement over the lifetime of the building due to surface decay and failure.
The purpose of this study was to map and record the decay exhibited on a
southern aspect of the building, which was due for restoration. In addition a
simple study was also undertaken on the early stone still existing from the first
building phase from other areas of the building and within differing
environments and which confirmed that decay forms commenced with a
change in limestone type used, particularly in this case from the Quarr stone to
the more micro porous Caen and similar limestones. Thus indicating porosity
as a factor in weathering. Laboratory analysis of samples was not available for
this study so the majority of observations and recordings were made on site.
A study of the climate of the region in chapter 2, indicated that although rainfall
for the region was low, humidity was relatively consistent and within the upper
range (60-90 per cent). Although wind direction was mainly from the southwest,
thereby removing any significant pollutants, the combination of low S02
and high humidity would fit in with the accepted environment for absorption of
atmospheric salts and associated crystallisation, hydration pressure and
expansion, leading to decay. Micro-climate analysis of an area of the southern
side also confirmed that the moisture content across the stone face was also
conSistently high and thus an indicator of a salt mobilisation and hydration
Chapter 3, which considers the building phases and materials used throughout
the building history of the Cathedral, also mapped an emerging pattern of
stone life for the various parts of the Cathedral, which tends to fit in with the
theory that the lithology of the same stone type may playa significant factor inIt is well established that atmospheric pollution is a major contributor to stone
decay but no major polluting industrial base has ever existed within the area of
Chichester, which was primarily an agricultural centre (historically a 'Staple
Town'). It was necessary therefore to establish the possible historic forms of
industry that may have contributed in some way to atmospheric pollution
thereby enabling the mapping of resultant pollution levels over time. The
analysis of this industry in chapter 4 has indicated that as expected the levels
of S02 were so low as to be almost inSignificant until the arrival of wide spread
coal use, and then even then they were very low. The amount may be
significant, however, when combined with high relative humidity.
The actual mapping and main photographic analysis of surface conditions
across three height ranges is undertaken and described in chapter 5. In a
number of cases, a relationship between black crusting and surface loss could
not be established, although, it was apparent that scaling and surface loss of
the sample areas was high. It became significant that decay was tending to
emanate from the lime mortar joints in a number of locations and situations.
This also became evident when looked for in other regions of the structure, for
example the north side of the Bell Tower, which had started to decay within a
forty-year period of restoration and is covered in chapter 6. Various forms of
mechanical breakdown were established but this research did not enable any
form of biological decay analysis to be undertaken.
the durability of samples.