Giovanni Borsoi

Microstructural Characterization of Consolidant Products for Historical Renders: An Innovative Nanostructured Lime Dispersion and a More Traditional Ethyl Silicate Limewater Solution

The conservation and durability of historical renders must be carried out through compatible techniques and materials. An important operation is the restitution of historical renders cohesion, turned friable by the loss of binder, usually due to physical and/or chemical actions. Surface consolidation is based on the use of materials with aggregating properties. This operation is reached usually through the application of organic or mineral consolidants, but inorganic consolidants are becoming preferred due to better compatibility and durability. In this article two mineral compatible consolidation products were studied: a commercial suspension of calcium hydroxide nanoparticles in propanol and a limewater dispersion of ethyl silicate. Microscopy (optical and scanning electron microscopy) and X-ray microanalyses of the consolidation products and of the consolidated mortar specimens were carried out. To assess the mechanical properties and products efficacy, analyses of the compression, flexural strength, and superficial hardness were performed. Microscopy results show that limewater dispersion of ethyl silicate forms platelike silica gels, which can interfere in product penetration. Otherwise, nanolime particles permit homogeneous distribution and optimum penetration on the treated substrate, improving cementing action and the agglomeration process.

Consolidation and chromatic reintegration of historical renders with lime-based pozzolanic products

Abstract Historical renders are exposed to several degradation processes that can lead to a wide range of anomalies, such as scaling, detachments, and pulverization. Among the common anomalies, the loss of cohesion and of adhesion are usually identified as the most difficult to repair; these anomalies still need to be deeply studied to design compatible, durable, and sustainable conservation treatments. The restitution of render cohesion can be achieved using consolidating products. Nevertheless, repair treatments could induce aesthetic alterations, and, therefore, are usually followed by chromatic reintegration. This work aims to study the effectiveness of mineral products as consolidants for lime-based mortars and simultaneously as chromatic treatments for pigmented renders. The studied consolidating products are prepared by mixing air lime, metakaolin, water, and mineral pigments. The idea of these consolidating and coloring products rises from a traditional lime-based technique, the limewash, widely diffused in southern Europe and in the Mediterranean area. Consolidating products were applied and tested on lime-based mortar specimens with a low binder–aggregate ratio and therefore with reduced cohesion. A physico-mechanical, microstructural, and mineralogical characterization was performed on untreated and treated specimens, in order to evaluate the efficacy and durability of the treatments. Accelerated aging tests were also performed to assess consolidant durability, when subjected to aggressive conditions. Results showed that the consolidants tested are compatible, effective, and possess good durability.

Application Protocol for the Consolidation of Calcareous Substrates by the Use of Nanolimes: From Laboratory Research to Practice

Abstract Calcareous materials such as limestone and lime-based mortars, widely used in the Built Heritage, are often subjected to degradation processes that can lead to loss of cohesion and material loss. Consolidation of these materials with liquid products via the surface is a common practice; however, the most used consolidation products (e. g. TEOS-based) show a poor physical-chemical compatibility with calcareous substrates. For application on calcareous materials, the so-called nanolimes, i. e. dispersions of lime nanoparticles in alcohols, are an alternative to TEOS-based products, thanks to their chemical compatibility with lime-based substrates. Nanolimes can help to recover a superficial loss of cohesion. However, their in-depth consolidation effect is not always satisfactory. Previous work has shown that a better deposition of lime nanoparticles in depth can be achieved by adapting the properties of the nanolime dispersion (kinetic stability and evaporation rate) to the moisture transport properties of the substrate, through optimization of the solvent. In this paper, freshly synthetized nanolimes were dispersed in pure ethanol and/or in binary mixture of ethanol (95 %) and water (5 %). These nanolimes were applied on Maastricht limestone and on a lime-based mortar by capillary absorption (method commonly used for laboratory tests) and by nebulization (method widely used in situ). The aim of this research is to fill the gap between laboratory tests and on site application, providing an application protocol for restorers and professionals in the field. The research shows that results obtained by application by capillary absorption do not always correspond to those obtained by nebulization. This fact should be considered when deciding on the use of a consolidation surface treatment in practice.

Nanostructured lime-based materials for the conservation of calcareous substrates

Social mix, a mixed population according to income and ethnicity, has been an important paradigm in urban development and housing and became the corner stone of renewal in post-war areas in the Netherlands in recent decades. In public as in academic debate, however, this concept has also been heavily criticized. The assumed positive effects of mixing for social cohesion and mobility would be limited or even negative. In this doctoral dissertation the central research question is: How do residents with different ways of life perceive and assess their changed and changing neighbourhood? The study in the post-war residential district Zuidwijk in Rotterdam focusses on the change as the result of autonomous moving processes in the existing social rental sector (the influx) as well as the result of demolition and new housing construction, often for owner-occupancy (the intervention). In general the residents of Zuidwijk are positive about their dwelling and immediate vicinity. They have experienced their move to Zuidwijk as a step up in their housing career. All residents value the green character and quiet setting of Zuidwijk, but are critical about the (shooting) incidents that happened in the past. The perception of residents from all clusters, be they Dutch natives or not, is that the influx in the existing social rental dwellings mainly, some even say totally, consists of households with a migrant background. The influx of mainly allochthonous households is seen as a problem by all residents. Dutch-native residents emphasize the negative effects on liveability and neighbourhood reputation and regret the loss of decorum and respectability. The allochthonous households emphasize the negative effects on integration and want to live in a mixed neighbourhood with Dutch native residents. In general the residents are positive about the impact of the social mix strategy: demolition and new housing development. Exceptions are found with the households of older allochthonous residents and allochthonous single-parent families. People in both groups have a low income and state that the new-built dwellings are not meant for them. Ethnic diversity is not seen as a problem in the population composition of the new-built houses for owner-occupiers. These residents have to work to be able to buy a dwelling and by doing so they ‘prove’ to be decent and respectable. Mixing makes a difference: it is important that the influx in the social rental dwellings not only exists of households with a migration background and a low income. Throughout the history of restructuring in Zuidwijk, the dominant narrative has been that the newcomers (meaning households with a migration background) did not have ties with the neighbourhood and only came there to obtain a cheap rental dwelling. This study disproves this narrative: a large number of them have come to live in Zuidwijk as youngsters and have grown up there. They identify themselves very strongly with Zuidwijk and, after a number of removals with their families, have rented or purchased a dwelling on their own. Ethnic diversity will become more normal while more and more allochthonous residents will grow up in the neighbourhood. The growing presence of allochthonous middle-class households in the new built houses may reinforce that. On the other hand the tensions and problems in the neighbourhood are heightened by the polarized national political debate about integration. The municipality and housing association do have an important role in acting adequately to signals and complaints of residents and supporting mutual contact of residents, but the austerity of the housing association and municipality in recent years has decreased the possibilities in this regard.