Castles of England/Construction Techniques
Castles in England have been constructed from a number of materials including stone, brick, timber, lead, iron and tin. To a large degree the choice of material for the main walls was driven by the availability of local supplies and, in later years, fashion.
The earliest castles were constructed primarily of wood, locally sourced as the transportation of felled timber over long distances was both impractical and expensive.
Work on the castle construction could not usually take place in the winter or early spring as it was too difficult to work in wet conditions. Even when work could take place, the sheer size of a castle meant it would take many years to build - for example, Dover Castle took 10 years to build.
For stone built castles the foundations would, wherever possible, been built directly onto the bedrock. The builders would dig down to the rock before leveling it to create the strongest possible foundation. The stones for the walls would be laid directly onto the bedrock. If there was no suitable bedrock or it was too deep, then a similar approach to that used today for buildings would be used. The builders would dig a deep and wide trench, then fill it with rubble that was packed down as firmly as possible to create a solid foundation. The wall stones would be built on the compacted rubble.
Walls were generally built of stone within wooden frames designed to hold the stone in place while the mortar dried. For thick walls, the wall was usually constructed with a cavity that was filled with rubble rather than being solid stone. Where strength was not so vital, the cavity sometimes contained a staircase. Scaffolding was used as the wall grew higher. It was held in place by inserting horizontal wooden scaffold beams into putlog holes built into the wall.
A moat is typically either a dry or water filled ditch. Most commonly it was constructed by expanding or diverting an existing watercourse. In some cases the castle would be built on a peninsula or even an island. In Guernsey, Castle Cornet goes even further and the sea performs the function of a moat.
Constructing a moat from scratch was a significant effort requiring hard labour.