Historic plasterwork and paint layers effectively complete the authentic image of plastered historic buildings [1]. Even so, the aesthetic and architectonic appeal of plasterwork on facades and the interiors of historic buildings is not by any means the only way historic plasterwork may speak to us.
Historic plasterwork is as a rule made up of strata from several periods, where each subsequent layer has been applied over the previous one, including period changes of the surface colour [2]. Historic plasterwork and its paint layers are in fact a type of archive, preserving traces of the post-construction development of a building, and containing evidence of the aesthetic feeling of our ancestors. It is material evidence of their proficiency in the craft and their technical skill, especially when we realise that historic plasterwork can last not just for dozens, but hundreds of years. However, historic plasterwork is an undervalued element of our cultural heritage; thus emphasising the protection of original plasterwork and paint layers is of utmost importance.
This article outlines the basic principles of gentle approach to historic plasterwork and paintwork protection. First and foremost, care for historic plasterwork is inter-disciplinary, combining specific expert knowledge and skills of many different specialists in heritage preservation: architects, designers, builders, monument technicians, often also art restorers, and last but not least, the craftsmen who do the actual work.
Providing care for historic plastered buildings and plasterwork is influenced by the fact that it is an inseparable part of the structure; moreover, the condition of the plasterwork is rather dependent on the structural technical condition of the building. Caring for historic plasterwork is thus only a part of the complex care of the whole building, and as such should not be viewed and treated as a separate issue.
Careful conservation of historic plasterwork rests on the experience that in most cases the plasterwork gets damaged not because of its insufficient durability, but mainly because, due to unsuitable subsequent adaptations (including bad, or complete lack of, maintenance), the plasterwork has been exposed to conditions ultimately leading to ruin [3]. Removing unfavorable circumstances - i.e. the causes of damage to the plaster - leads gradually to improving of the unsatisfactory state [4]. It is then possible to save even valuable originals that have suffered serious damage.
It is wrong to generalize and claim a concrete case of preservation of historic plasterwork as universal and generally valid. It is always an individual process, influenced by many factors, different for different buildings, conditions and quality of the preserved historic material.
The proposal of the means of renovation should be based on the results of research, it is necessary to respect the fact that this is an intervention into a historic construction and materials, so that their protection should be the main criteria for selecting the approach and the materials.
While preserving historic plasterwork, minimal intervention to the original is preferred to blanket surface replacement (reconstruction) of the plaster. This has to be preceded by improvement in the condition of the building, and renovation of existing plaster patches, which should blend in with the whole. Patches must be carried out using a high standard of workmanship, where the application, signature craftsmanship, surface structure and colour copy historic plasterwork in the vicinity of the renovated place.
The one thing to avoid is the unfortunately common current practice, where the first step in renovating historic plasterwork is stripping it off. It is foolish to believe that the newly-applied plaster will be better and last longer, and that the renovation will be less expensive. Furthermore, historic buildings with newly applied plasterwork hardly ever look authentic, and in cases where the underlying cause has not been removed, the same problems will show on the new plasterwork.
The choice of suitable material for the treatment of historic plasterwork is also influenced by specific individual discoveries in situ. In choosing the appropriate material for patching historic plasterwork, the principle is that the new patches must be compatible with the patched original, i.e. they should share not just the same composition as the original but the same method of application, as the quality of the materials depends not just their composition/structure, but also the way they were prepared. Hence materials and traditional approaches are prioritised i.e. in harmony with period handiwork [5].
Historic plasterwork is not only beautiful, but also very valuable. During its preservation the interests of investors often clash with the interests of conservationists. Investors will always assert the approach that prioritises the durability of the renovation, while the conservationists' task is to protect its unique preserved value. A sensible, systematic approach to the preservation and protection of historic plasterwork can undoubtedly suit both sides. However, it requires constructive communication on both sides to attain the common goal: a professional, distinguished, authentic and lasting result.
[1] It is possible to observe this dissonance in many cases, when authentic historic plasterwork has been unprofessionally repaired or replaced with new plasterwork.
[2] Very often, an analysis of the plasterwork of a Gothic structure reveals layers created by plasterwork created in the Gothic, Renaissance, Baroque and Neo-Classical periods and plasterwork characteristic of the 20th century.
[3] One of the main causes of damage to historical plasterwork is excessive damp in the walls, found particularly at the base or rising above, or under the roof, or in places of water leakage. Generally it is caused by secondary alterations, which prevent surface drainage of damp from uninsulated foundations (both in the interior-impermeable layer of flooring, and the exterior - impermeable alterations near the structure, e.g. asphalt pavements and roads). The collection of rainwater plays a significant negative role, when water gathers under a building instead of flowing into the drainage, then also unmaintained roofs and chimney units, which let water drip into buildings.
[4] Because the stabilisation of an originally bad structural condition of a neglected historic building is, as a rule, a long-term process, it is advantageous to plan work connected with the conservation of the plasterwork for the moment when the condition of the building begins to visibly improve.
[5] While traditional craft and technology is of independent cultural value and cultural heritage, their existence is in direct connection with the existence of historic objects.