The Boom in Nanomaterials for Built Heritage Conservation: Why Does Size Matter?

There is no doubt that nanotechnology and nanoscience open new doors to new applications and products that can potentially revolutionize the practice field and how we conserve built heritage materials. However, we are living at the beginning of this era and the potential benefits of nanotechnology to specific conservation practice needs are not always fully understood. This opinion/review paper aims to present reflections and answer a question that we are often asked when working directly with stone field conservators: why should we use a nanomaterial instead of a conventional product? Why does size matter? To answer this question, we revise the basic concepts of nanoscience with implications for the built heritage conservation field.

Effectiveness and durability of anti-graffiti products applied on ETICS: towards a compatible and sustainable graffiti removal protocol.

External Thermal Insulation Composite Systems (ETICS) are widely used constructive solutions which aim at enhancing the building thermal performance. Nevertheless, ETICS can often present anomalies (e.g., stains and microcracks) throughout their service life, and vandalism actions, as in the case of graffiti, are rather common in urban areas. The removal of undesired graffiti is generally carried out through invasive chemical-mechanical methods, which may affect the durability of the ETICS. The adoption of anti-graffiti products can be a feasible protection method; however, no comprehensive studies were already addressed on these substrates. This study aims at evaluating the effectiveness, compatibility, and durability of three anti-graffiti products (with permanent, semi-permanent, and sacrificial properties) when applied on different ETICS. The removal of aerosol graffiti paints was carried out with a low-invasive and eco-friendly removal method (i.e., low-pressure steam jet). The water transport properties, as well as color, gloss, and roughness, were evaluated before and after graffiti removal. The durability of the anti-graffiti was also assessed by artificial aging cycles. Results showed that graffiti removal was rather efficient on ETICS with acrylic-based finishing coats and when using (semi) permanent anti-graffiti products (with ΔE*ab < 5, i.e., not macroscopically visible, when comparing cleaned and reference surfaces), although these products can reduce their effectiveness after aging. Conversely, unsatisfactory graffiti cleaning was observed on ETICS with lime-based or silicate-based finishing coats (with ΔE*ab > 5), with considerable alteration also of the water transport properties (reducing water absorption and slowing down the drying kinetic).

Advances in Nanolime and Other Nanomaterials for Built Heritage Conservation.

This Special Issue examines the synthesis, characterization, and manufacturing of nanoparticles and their potential advantages and applications for the conservation of built cultural heritage materials [...].

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 product's 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.