Technical restoration of stone surfaces


The design process required for the definition of an effective restoration, whether it concerns the monumental historical building that modern architecture, must necessarily start from a thorough knowledge building or the structure on which you operate. For this it is essential to proceed, in a first phase of work, to a campaign of analysis that allow to define in detail the characteristics of the constituent materials of the building and its state of preservation, with the goal of specifically understand how the building is done, which interventions transformed the building through time and how will it stand in the future. Through this journey of discovery you will be able to more effectively identify the most appropriate restoration methods in terms of compatibility and durability.
The modern building restoration therefore must be faced starting from the methods and construction techniques of historic building appropriately adapted to these contexts, taking into account the fact that, compared with the historical building, you can collect more information: often you can have the original project, the successive variants and architectural changes, and sometimes you can even talk directly to those who have worked (the designer, operators, etc.). Compared to historic building, there is also a greater possibility of application of innovative techniques, methods and materials (vacuum consolidation systems, laser system, nano-materials).
As part of the workshop organized by the Association and the Foundation Architects Florence, in collaboration with Assorestauro and the Order of Engineers of the Province of Florence, we carried out a practical demonstration of some of the analysis and restoration methods applicable to modern construction surfaces at the building that hosted us (the Royal House of Santa Maria Novella Station) and at another building made available by RFI: the boiler room of Santa Maria Novella station. In detail, in the Royal House we did a thermographic analysis (aimed to identify thermal anomalies such as moisture infiltration from the outside and to understand the structural morphology identifying for example the pillars, the horizontal structures, the warping of the floors support), the absorption analysis of different stone materials, microscopic analysis of surfaces, the pacometric analysis on the covering stones for the detection of the position of metal anchoring elements that were in part not more effective, up to require a recent fixing intervention by insertion of pins from the outside. It was, as mentioned, a series of demonstration analysis that have allowed to preliminarily understand some significant features of the building surfaces. In particular it was possible to detect the presence of an extended protective treatment presumably applied during a maintenance intervention of the ‘90s of the XX century on the surfaces of the stone slabs made of Marble “Fior di Pesco Carnico” and partly removed in the course of recent interventions of removal of graffiti vandalism. On the basis of these considerations we conducted a series of samplings examples of restoration interventions aimed in particular to identify the most suitable methods for the cleaning treatment of the surfaces treated with the protective coat partially removed and for the extraction and removal of the products of corrosion leachates from metallic elements. The samples were carried out using different methodologies supported such aqueous gels, gel added with ammonium carbonate, gelled solution with non-ionic surfactant, the solution gelled in agar agar, etc; in most cases chosen to increase the “wettability” of the surface and thus in- crease the capacity of the deposits removal while maintaining the existing protective layer. Regarding the Thermal Power Plant of the Santa Maria Novella station, we performed some demonstrative analysis such as thermographic investigation of the surfaces (with the dual purpose of understanding the structure of the building in relation to the system of floors and pillars, and identify abnormalities linked to moisture concentration); stratigraphic analysis of coatings (functional to define the macroscopic characteristics of the finishes during the various construction and modification phases), analysis of the architectural elements (functional to understand the evolution of architectural elements from development to the present day). It was also possible to correlate the on-filed analyzes data with the information obtained from the project documents provided by RFI (regarding both the building process and the subsequent architectural transformations).
The most significant issue emerged by this analytical phase is the direct detection of traces of a modification work made in the middle 70s of the twentieth century that led to the drafting of a new plaster coating painted on the surfaces of the entire building (covering the original finish of the 30 detected by the stratigraphic tests) and the amendment of the openings of the Via delle Ghiacciaie front (as revealed by analyzing break points, and graft of the curbs in squaring travertine of the windows).
The analyzes have also led to detect general degradation phenomena such as surface dirt deposits and biological deposits on travertine elements, paints and graffiti vandalism on plaster, stone, stained glass and metal elements, oxidation of metallic elements, consistent deposits on interior flooring surfaces. We therefore carried out some exemplifying samples (such as cleaning with use of prepared polymeric water-based, with supporting gel of agar-agar base, with paper and saturated ammonium carbonate solution; use of appropriately formulated mixtures for the conversion of the corrosion products and for the finishing of the metal elements), aimed at eliminating the degradation problems described above with suitably calibrated methodologies, based on material type and state of preservation.

[by Rossana Gabrielli, Francesco Dall’Armi]