In the study on the repair and maintenance of historic plasterwork, observations and information from practical tests, ongoing construction sites and laboratory analyses were gathered. Given the great diversity of modernist plaster, the team decided to focus mainly on similarly painted plaster and, in particular, on how to clean and repair it.
Encountered situations and working principles
The study uses basic principles in the conservation practice of historic buildings, whether listed or not. However, these buildings that form the basis for the observation are part of protected areas, where the appearance of the facades determines the character and value of the area. As a result, we list situations, encountered in this study, where basic principles used in the conservation of historic buildings have been used:
Interventions on historic plasterwork, whatever their nature (cleaning, completion, repair, consolidation, etc.) should use the principle of minimal intervention, only where strictly necessary and as far as possible reversible. Interventions should not affect the original material in the long term, so as not to hinder possible future conservation processes that may be carried out with other more modern methods that may emerge in the years to come;
Façade rendering preserves the character, value and historic significance of a historic building. Irreversible processes of intervention can destroy these essential features of the built historic heritage, limiting access to this heritage for future generations;
Regardless of the nature of the interventions carried out on historic plasterwork (cleaning, completion, repair, consolidation, etc.), the preservation of authenticity – those attributes and elements that most truly reflect the heritage values of the building in question (texture, decoration, plastering technique, craftsmanship, aesthetic value, etc.) – must be taken into account.
Observations and recommendations
Halfway through the project period, we present some of the project team’s observations and recommendations:
Façade damage should be carefully investigated and analysed. This is done through a facade survey, which includes analysing the material and understanding the causes of degradation. Unfortunately, façade renovation interventions are not based on this analysis and repair/restoration decisions are often based on superficial information. The most common solutions are either to replace the façade plaster with an imitation, as far as possible, of the texture, or to paint over the existing plaster; these solutions lead to irretrievable losses of technique and historic substance. Unfortunately, it is not always possible to carry out a sufficiently thorough analysis of the facade prior to the start of construction work, when there is no access to the entire façade surface (scaffolding) and no possibility of collecting information on the physical and chemical behaviour of the façade material. Material analyses can be expensive and relatively time-consuming, but in order to base the choice of intervention materials it is necessary to assess at least the hardness of the plaster layer and its porosity, even if only at an empirical level;
New material additions (even when made with the same type of material) will not be identical due to the ageing of the original plaster (in the case of stone-like plaster, the erosion is similar to that of natural stone). However, where they are necessary, they should be made with a material of similar porosity and hardness to the original, which meets the appearance requirements if the exact composition of the original material cannot be reconstructed. Cracks in the surface of the simulated stone often result from the workmanship process and do not necessarily represent damage requiring repair;
– Façade renovations should not bring the façade to a “new” state, but should ensure the stability of the finish and preserve or improve the weather-resistant qualities. Cleaning does not mean that the appearance has to be “like new”, it is normal/recommended to preserve patina, imperfections and any harmless degradation (discolouration, weathering…) that does not jeopardise the stability of the surface. In the case of hard cement plaster, there are micro-cracks which have appeared with the processing of the material, but which are stable over time, unless aggravating factors (broken gutters, uncontrolled vegetation, etc.) have occurred;
Façade renovations should not bring the façade to a “new” state, but should ensure the stability of the finish and preserve or improve weather-resistant qualities. Cleaning does not mean that the appearance has to be “like new”, it is normal/recommended to preserve patina, imperfections and any harmless degradation (discolouration, weathering…) that does not jeopardise the stability of the surface. In the case of hard cement plaster, there are micro-cracks which have appeared with the processing of the material, but which are stable over time, unless aggravating factors (broken gutters, uncontrolled vegetation, etc.) have occurred;
Interventions on small areas cannot always be extended to large façade areas, given the costs of labour and materials. Some of the consolidation tests were done with methods that were far too complex and could not be applied on a large scale (e.g. consolidation injections), but brought into question the need for proper assessment of the damage: how serious is the crack? Is there a risk of detachment?
The plaster recipes used are extremely diverse. The project worked with three laboratories, which allowed us to observe differences in the results generated by the analysis methodology. At the current stage of the project it is still too early to draw any relevant conclusions, as a large part of the analyses started are still in progress.
But what we have observed and discussed with material suppliers is that today’s materials are not identical to those used in the early 20th century, due to differences in production (e.g. cement) and even in the raw materials from which they are made. It is therefore important to find the optimal compatibility, based on physico-chemical behaviour.
The study will not provide standard solutions because each case is unique, but the principles and recommendations for approach can provide support for interventions that better protect valuable textures and even help to lower intervention costs. We are working on a set of recommendations for intervention steps for the rehabilitation of historic modernist façades, as well as recommendations for technical specifications (about material and intervention methods) for projects and specifications.
“Forgotten Textures – Historical Plasterwork. Research and practical studies for repair and maintenance” is a project carried out by Pro Patrimonio Foundation. supported by the Order of Architects of Romania from the Architecture Stamp and PSC Group.
