Historic English Churches

A Guide to Their Construction, Design and Features

Geoffrey R. Sharpe

• Publisher: I.B. Tauris
• Year: 2011
• ISBN:
  9780857731142
• Edition: 1
• Topic: Architecture
• Subtopic: Religious Architecture

The ancient churches and cathedrals of England's towns and countryside are among the glories of our national heritage, the church spire one of the quintessential features of the landscape. Yet how were our ancestors able to construct these often substantial edifices without the benefit of modern techniques? How did medieval masons plan, design and oversee their construction? What methods of construction were used to achieve the magnificent church spires and ceilings that we marvel at today? Geoffrey R. Sharpe brings more that forty years of experience of managing and caring for historic buildings to provide a unique guide to the design and construction of our historic churches and cathedrals. Building a cathedral could require a workforce of 300 to 400 men, the quarrying of 80, 000 tons of stone and involve the felling of 1500 trees. How all this was organized, managed and realized is explained in this compelling volume. The author deals with all aspects - from original planning and preparation, to the final construction and decoration. The layout and choice of materials, the construction of the foundations, walls and ceilings, the work of the highly skilled medieval masons, blacksmiths and carpenters are all described and explained. Individual aspects of church architecture such as corbels, tracery and windows, as well as important features of church interiors such as galleries, burial vaults and screens are included. And in a final chapter the author shows the reader how to assess the history and development of a church from the constructional and architectural clues contained within its features. The result is a work that will add a whole new dimension to understanding English church building and architecture.

1 The Construction of Churches

Cements and Concrete

Lime and Cements

The use of mortar enables bricks and stones to be bonded solidly together so that stresses from superimposed loads can be distributed. It also reduces to a minimum voids or paths through which air or moisture might penetrate the structure. Many people do not realise that, in addition to taking compressive forces, mortar also has a function in the transmission of shear and tensile forces. A loss of strength will occur if the bond between the blocks and the mortar fails. The lime or cement in the mortar is termed the matrix and the sand the aggregate. These are mixed to the proper consistency with clean water in different proportions, depending upon the type and character of the work. The mineral content and natural pigments in the sand can affect colour, and the quality of the lime or cement determines the strength. Although they are rare in church walling, black mortars can be seen from time to time. Accounts at Westminster dated 1532 refer to the use of black mortar in flintwork. Lamp-black or burnt moulding sand from the blacksmith seem to have been the most preferred ingredients, but ground ashes and ground clinker are also mentioned in old accounts.

The mortars used in early church building were always a mixture of lime and sand, and it has long been assumed the ratio was generally one part of lime to three equal proportions of sand. However, a large number of analysed examples, especially those from the earlier medieval churches, have been found to be 1:1½ or 1:2, and further research has revealed the proportions can sometimes vary within the same structure. It seems that where there was a need for extra strength or better weather protection it was often the practice to increase the ratio of lime to sand.

The lime was originally produced by calcinating in a wood kiln (calcifornium) either limestone or chalk to a high temperature, which had the effect of removing the calcium dioxide content. Coal-fired kilns did not come into normal use until the Industrial Revolution. After kilning, the resultant quicklime had to be slaked with water until it was hydrated, and the mixture was then turned over with a shovel on a boarded platform with, if necessary, more water being added until the correct consistency was achieved. The lime could then be mixed with sand and used as mortar, although for certain works lime putty was needed. Lime putty mortar is a soft plastic paste made by mixing one part fat lime and three parts by weight of water. The term ‘fat’ was given to the rich lime derived from the more pure white chalk deposits which are non-hydraulic (they can only set by reacting with carbon dioxide in the atmosphere) and are slow to set. After mixing, the lime putty mortar was left until it stiffened into a pliable and workable condition, when it is ready for use. With especially fine jointing some masons preferred to use a mix of one part lime putty to three parts of crushed stone dust.

In the British Isles most of the limes produced in this way were non-hydraulic, giving a setting process which slowly converted the slaked lime back into calcium carbonate. A limited number of formations, such as the blue lias deposits, however, contain contaminants of silica, clay, alumina and iron, which gives them hydraulic properties that enable them to set in the presence of water without the total reliance on carbonation. These limes were originally known as ‘water limes’, and the various constituents can continue to harden when under water to form calcium silicates and calcium aluminates. They are usually identifiable through their colour, in various ranges of grey, buff or reddish brown. In the presence of moisture all natural hydraulic limes have varying levels of hydraulicity because of differences in composition and in the integrity of the kilning. These variations were originally classified as: ‘eminently hydraulic’, which gave a setting time of one to four days; followed by ‘moderately hydraulic’, which takes between five to fifteen days; the slowest was the ‘feebly hydraulic’, which takes around fifteen to twenty-one days. This has now been amended under British and European Standards to include strength after twenty-eight days.

Non-hydraulic limes can be given some hydraulic properties through the addition of a pozzolanic additive such as crushed brick, tile or earthenware. The term pozzolan comes from the Roman practice of using volcanic ash from the region of Pozzuoli near Naples for the same purpose. From around the beginning of the seventeenth century onwards much experimentation went on in the manufacture of various hydraulic cements. In 1796 James Parker patented a new cement he called Roman cement produced from argillaceous clay (septaria), found in the seabed around Harwich and the Isle of Sheppey. Kilned at a low temperature, it was not only hydraulic but also proved to be most durable and could withstand persistent damp. Unless it was retarded it had a quick setting time of between twenty and forty minutes, making it an ideal material for working in locations affected by tidal waters or under heavily saturated conditions. As a mortar it was generally used in the proportions of 1:1½ or 1:2 with evidence indicating that stone masons preferred it for fixing cement joggles (see below, Fig. 32). Its high level of iron oxide makes it identifiable by giving it a distinctive dark pinkish-brown colour. Similar cements followed, such as Medina cement, which was made from clay taken from the beds of the river Medina on the Isle of Wight and is much lighter in colour. All these cements attained greater strength than hydraulic lime but less than Portland cement.

In 1824 Joseph Aspdin patented Portland cement, which eventually brought about many changes to the building process. The original product had some deficiencies, but in 1845 Isaac Johnson improved the quality by kilning to a higher temperature, giving considerably enhanced properties. In masonry this gradually led to the widespread use of ‘compo’ – the name often given to cement–lime–sand mortars – a practice which continued up to the end of the Second World War, the usual proportions being one part cement, two of lime and nine of sand. Records going back to the mid-eleventh century indicate that in conditions of excessive damp it was often the practice to use a special cement compounded from either wax and pitch or wax and resin, which was applied in a molten state. The research for this book did not reveal any direct evidence of this having been specified in church work, but there can be little doubt that it would have been used where there was a pressing need to guard against damp.

Concrete

The use of concrete is often perceived as being a relatively new development, but in reality its origins go back to the early civilisations, at least as far as the Ancient Egyptians and the Chinese. Moreover, archaeological evidence indicates that both the Greeks and the Romans had a full understanding of how to adapt and apply concrete to best effect. The word concrete comes from the Latin concretus, which means ‘combined as one’. The concrete produced in Britain up to Norman times has been found to have a close similarity to that made by the Romans, with the constituent materials being in much the same proportions. It was frequently used as a core material in walling, a perfect example being the abbey ruins in Reading, where the wall facing has either been pillaged or has fallen away to expose the concrete hearting. In addition to the chemical set, all untempered natural hydraulic limes in the British Isles require a certain amount of carbonation from the atmosphere to achieve full strength. This is a reaction which cannot occur underground, which is the main reason why concrete was not generally used in foundation work during the medieval period. It is likely that other problems would have arisen over the strength and setting of the concrete as a result of possible damage from iron pyrites, salts, shale and mica in the ground. Some mineral salts in the ground water also had the capacity to reduce the quality of concrete. Nevertheless, the medieval masons were aware that by introducing an artificial pozzolanic material such as trass, crushed brick, tile or even broken-down earthenware the strength and hydraulic properties of the lime could be considerably increased. By the late seventeenth century pozzolanic rock was being imported from Holland to make hydraulic concretes and mortars. It came from a natural formation at Andernach in Germany where it was quarried and shipped in lumps to Holland, and then pulverised and exported as ‘Dutch terras’. As the constituent materials improved and developed, lime concrete continued to be used until well into the nineteenth century.

Foundations (Fundamentum)

The skilled masons of the medieval period had a good understanding of the basics of constructional stability and they built to proven and well-tried methods. The conclusive evidence is in the large number of cathedrals and churches which have stood on the original foundations to the present day. The lack of any need for major intervention has resulted in much foundation work remaining concealed, and as a result there is still much to be learnt. For a better overview it has been necessary to search old specifications and contract documents. Investigations have revealed much clear and precise information: in some cases the dimensions and statements relating to trench depth and width indicate that the builders had a full appreciation on how downward and lateral pressures needed to be resisted. While they lacked any knowledge of structural engineering in the form we use today, they were nevertheless able to produce a satisfactory outcome through a combination of accumulated knowledge from the past, accurate onsite observations and intuitive judgements. The intricacy, volume and height of the churches they built were considerable achievements; without any scientific awareness they were able to deal with the complexity of the different stresses caused by compression, tension and shear in materials and components, using practices handed down from one generation to the next. This is very much in contrast to the methods now used, by which stress and strain can be accurately calculated by means of mathematical formulae.

Stress can be briefly defined as the cohesive force by which the particles of a body resist an external force. It acts in a number of different ways, such as compressive, tensile, vertical, horizontal and transverse stresses. Compressive stress occurs when forces compress a material or push the particles closer together. The opposite force is tensile stress, in which external forces cause either the stretching or pulling apart of particles away from one another. Vertical stress arises from a tendency of a beam to shear under load, whereas horizontal stress occurs if two opposite forces acting on a material are not quite in line; this results in a tendency for the fibres to fail through a sliding action. Forces which cause bending stress result in the top fibres in a beam becoming shortened and those at the bottom being lengthened. A more complicated form of stress is transverse stress, which can arise from a combination of tensile, compressive and shearing stress. Strain i...