Preparation and construction

The site was first levelled and cleared and the size and shape of the building marked out using wooden pegs and string. The foundation trenches would then be dug. The trenches were first filled with a rubble and mortar mixture, then retaining walls were built on top to just below ground level and the space between them filled with more rubble and mortar. Castles usually contained two types of masonry, rubble and ashlar. Rubble was lumps of irregularly-shaped stone, which was used for walls that were not going to be visible as it was cheap and easy to lay. Ashlar was good quality, regularly-cut stone that was used for exterior walls and was more neatly laid and jointed.

The transportation of stone and other building materials was a logistical problem for medieval master masons. If feasible, a quarry was established as close to the site as possible. If a quarry could not be set up nearby then the master mason may have to obtain the necessary stone from independent quarry masters. With transport by road being slow, cumbersome and expensive the ideal way to convey the stone to the site was to use navigable rivers and waterways. Transport was a major source of expenditure in castle building. At Caernarvon Castle in Wales the total amount spent on materials in 1285-6 was £151 5s 6½ d, but the cost of transporting the materials came to £535 8s 8½d, in other words over three and a half times the cost.

Mortar for the walls was prepared by burning limestone or chalk in kilns to produce quicklime. This quicklime was then mixed with water to produce lime putty, to which sand was added. This mixture was then turned into mortar with the aid of a mechanical mixer; this was a circular well with a vertical centre-post to which was attached a horizontal beam with paddles. When the beam was turned the paddles stirred the mixture into mortar.

Lime mortar was time-consuming to build with. It takes a long time to go off (set) and because of this only a limited section could be built at a time before needing to wait for the mortar to set - sometimes up to a week. If you carried on building before the mortar was set then the weight of the walls would push the mortar out and there would be very little holding the wall together. Even today if you go right into the centre of a castle wall built 800 years ago you may find that the lime mortar has not completely gone off.

Lime mortar also required certain weather conditions. If it was raining or damp the mortar could wash off or take longer to set, if it was too hot then the stones off the wall would need to be kept damp to stop them absorbing the moisture from the mortar and preventing it from sticking.

The stone cutters in medieval castles were supplied with patterns of the stone carving details from which to work. Using compasses and a square, the master mason drew all the patterns out in full size on specially prepared plaster floors. These designs were then used to create wooden templates, which were given to the stone cutters. The stone cutter would then square his block to size, draw the outline of the template on each end of the block, and then cut it to shape. Today stonemasons still use templates to mark out the design on the stone before carving the decoration, however today templates are made out of hard-wearing plastic rather than wood, which is prone to rotting. 

The tools of the modern stonemason have changed very little since the medieval period. Stonemasons from Capps & Capps (who have worked extensively on Hereford Cathedral) still use simple metal chisels, lump-hammers and pairs of compasses to carve the blocks, the only difference today being that often the chisels are tipped with titanium which makes them considerably more robust than those of a medieval mason. Today a stonemason undergoes a seven-year apprenticeship which teaches him all about the working and carving of stone. It is likely that these skills were learnt in much the same way in the Middle Ages, with a lot of the learning taking place on the job. 

The finished blocks of stone would have been quite heavy, and the medieval builders developed several ways of lifting them into place on the wall. One way was to set up a system of jibs and pulleys where the turning of a wheel pulled a rope, which raised the stone. In larger castles these pulley systems could take the form of a treadmill attached to a large wheel, which was turned by a man walking round inside of the wheel.

Construction in the medieval period was often seasonal, with building being undertaken during the six months of the year when the weather was more conducive to working out of doors. Lime mortar has an extremely slow setting time, which would have meant that it was vulnerable to being washed away in bad weather. The slow setting time would have also meant that the height of construction in one day would have been limited as upper levels could not be laid until the mortar had dried below, giving a stable base on which to work. Dr. Warwick Rodwell (in The Archaeology of the English Church, Batsford, 1981) has estimated that medieval buildings were erected at a rate of 20-50cm a day.

[Original author: Miranda Greene, 2002]