Using Traditional Materials & Techniques
Lime Production In Scotland
Repair And Maintenance Strategies
Before undertaking a programme of repair works, careful investigation is required to establish the original materials and to understand the dynamics of the building. Investigation and understanding of the architectural development of a historic building have long been accepted as the norm, whilst current practice also puts emphasis on the social and cultural importance. Alongside these concerns, an understanding of the technology of the building is essential if repairs are to be effective. Effective repair of traditional buildings relies on his holistic approach, taking account of the overall behaviour pattern of the building and its local environment.
Traditional permeable mortar materials require an overall environment of good building repair to maintain their decorative and protective qualities. Where other buildings elements are not adequately maintained, the poor performance of traditional mortar materials, whether in the form of coatings or jointing mortar, will be compromised. Once the dynamics of building performance, including patterns of decay, have been understood, a strategy for conservation or repair can be developed. In the past, the decay of lime harling, for example, has too often been regarded as an underlying failure of the material. This has led to its replacement by cementitious coating without investigation and resolution of the casual factors of failure, such as inadequate maintenance of rainwater goods or inappropriate building details.
Repairs might be required to jointing mortar, due to either gradual deterioration over many years, or, for example, to lack of maintenance of rainwater goods. Reinstatement of lime mortar jointing might also be required following inappropriate cementitious pointing, where the hard mortar has encouraged exhilarated decay in the stones themselves.
External lime coatings can survive for several hundred years given a favourable environment and appropriate building maintenance, but more frequent renewal is often necessary. Removal of cementitious coatings and the reinstatement of lime finishes is a common requirement. It will also be found that cement renders have trapped moisture in the wall fabric, leading to dampness, timber decay and, of course, to stone decay associated with the presence of sulphates or other salts behind the cement render.
The Life Expectancy Of Traditional Building Materials
Internal lime plaster finishes normally survive for a long period, except where decay or movement of timber substrates cause mechanical failure. Most internal plasters before the early 20th century are lime based, although many from the 18th century onwards all also have small gypsum content. The behaviour and properties of modern, wholly gypsum-based plasters are significantly different from those of lime-based plasters and these never newer materials should never be used to patch traditional plasterwork.
Techniques for use of traditional mortars, renders and plasters require skills which have been learned by practice. Major repair or reinstatement of and clay-based mortars should be only tackled by workers familiar with the materials and their properties. Similarly, the repair and reinstatement of lime-based materials require an informed approach.
Unfortunately, modern lime materials and skills do not, at present, always achieve the long activity of many traditional applications – but we are working on the problem. The successful use of
new lime mortars depends both on the materials themselves and on appropriate conditions and techniques of use. Skilled craftsmen and good site practice are of fundamental importance, as is the availability of high quality, durable lime mortars. The former can be addressed by training and the latter by research and development work, such as that currently practised at Charlestown in Fife.
The life expectancy of traditional permeable mortar materials can be directly influenced by any of the following: availability and selection of an appropriate good quality mortar; techniques and quality workmanship (including effective preparation of materials and backgrounds, removal of vegetation, careful and knowledgeable application and appropriate curing after application, usually involving some form of protection; building details; local environmental conditions; and the maintenance regime.
Traditional masonry buildings require regular routine maintenance as well as long-term maintenance. For many building owners a simple routine of checking, and do it yourself or local tradesmen care on the level of housekeeping maintenance, would minimise the need for large-scale repairs. At this level special skills are not essential – a commonsense approach and a basic understanding of the building and its materials are all that is required. For those owners who do not feel sufficiently confident to tackle basic housekeeping maintenance, help is at hand. This comes in the form of short courses or one-day workshops run by the National Trust for Scotland, the Society for the Protection of Ancient Buildings, and the Building Limes Forum, the Scottish Lime Trust
Regular Building Inspections
Maintenance requirements for buildings containing earth and clay involve regular inspection and prompt making good of minor defects by patching in with matching materials. No alien materials should be introduced and the use of cement-based mortar or modern paint systems must be totally avoided. Earth-based materials rely on an appropriate level of moisture – if they become totally dried out they will crumble and disintegrate. On the other hand, too much water will also cause failure.
Where buildings have a limewash finish, routine housekeeping maintenance on a domestic scale can be undertaken very simply by brush application of a limewash to minor defects if and when necessary. Limewash can be kept in a resealing container for this purpose. Similarly, minor degradation of harling can be patched in by hand, using a matching ready mixed lime mortar kept for this purpose (Premixed basic lime mortars be stored for long periods of time.)
Traditional domestic buildings almost invariably contain permeable mortars, either lime-based or, less frequently, earth based. These may be in the form of construction mortars, external coatings or internal plaster finishes. Effective performance of these mortars is critical to the overall well-being of a building and, conversely, effective maintenance of a building is required to ensure the performance of mortars. A holistic approach is required to the care of traditional buildings. Major repair or reinstatement of traditional mortar materials requires selection of appropriate materials and informed and skilled workers; but with a little understanding, common sense and enthusiasm, owners or local tradesmen can tackle routine housekeeping maintenance which, performed regularly, will significantly reduce the need for major repairs.