The walls of the Butser Roman Villa follow the archaeological evidence from the Sparsholt Villa and do not have foundations as such. The wall is set directly on the chalk platform, with no foundations and built up from there. There is no damp course to stop moisture travelling up through the walls, because there was no archaeological evidence for this at Sparsholt and walls made with lime mortar 'breathe' of their own accord.
You might be puzzled as to why the walls are so wide given the relatively small area that the timber framing occupies on top of it. The width of the walls is based on the excavated Sparsholt site and they are the same thickness throughout the villa. If the walls were built solely for load-bearing capability, this would be curious, as there should be thinner walls to the exterior of the corridor. On the other hand, if the roof structure was carrying the load onto the outer walls of the villa (including the corridor), why were the inner walls not thinner? Perhaps the walls were 'over-engineered' to be on the safe side? We did find during construction, that, at times, in the UK climate, the walls took rather a long time to develop sufficient strength to take the weight of the next layer. The strength development and stress pattern in such walls is complex and depends on the way the flints are used, as well as the way the core is filled, so it is difficult to decide if this could have been a consideration in the choice of wall thickness for Sparsholt and similar villas. In any case, this would not explain the structural anomaly of using thick walls throughout, regardless of the load any was subjected to.
The lower two metres at Butser were built out of flint and lime mortar. The Roman acquisition of flint would have been easy, as the flint nodules still lie all over the fields, turned up by cultivation. However, the majority of our material came from sea-dredged sources. This needed to be picked over to select the useful flints. This phase of bringing the material onto the site took up about 20% of the building time. Approximately 200 tons of flint were used in building the walls to this height.
To make lime mortar, you first have to begin with limestone or chalk. This has to be heated to around 1000deg C, during which process it releases carbon dioxide. It is then called quicklime. Next it is wetted with water, which forms slaked lime. The water hydrates the quicklime, giving off so much heat with the chemical reaction (it is quite a dangerous process) that water spitting may occur. The final form is putty-like. This putty is then mixed with a material such sand to make the lime mortar. About 20 tons of quicklime were needed for the walls and about 7 tons for the plastering and rendering.
The building technique for the wall depends very much upon the use of flint. Flint is knobbly and irregularly shaped. So the lime mortar is needed to fill in the gaps and holes between the flints and to bond them together. Long flints are used across the wall to help bond or 'lock' the structure together. The rate of building was around one cubic metre per person per day.
The upper part of the walls is timber framed, with a lot of gaps. These can be filled in with a variety of materials but the technique used at Butser is that of wattle and daub panels. This has the advantage of using locally sourced materials. Hazel rods are cut and woven into a lattice between the main timbers. They are then coated in daub, which is a mixture of earth and straw or grass. When the daub has dried, it can be plastered with the usual lime plaster and then painted if desired. The 'normal' agricultural style of making wattle panels is for uprights to be inserted in the panels and then for the thinner rods to be woven horizontally. There is also a Roman technique, where larger flat battens are set horizontally and the wattle is then woven vertically. It has been suggested that this method allows for prefabricated wattle panels to be inserted in slots running down the upright timbers.
Created 15 November 2003 - Updated 15 November 2003