Influence of treatment technique on the effectiveness of nanolime as a consolidant for low-porosity limestones

Due to its high compatibility with any carbonate substrate and acknowledged efficiency, nanolime is one of the most promising stone consolidation products on the market, to date. However, its performance remains limited when applied on limestones characterised by low porosity (η < 20%). It has been acknowledged that various factors can affect the performance of nanolime. In this paper, the impact of the treatment technique on the efficiency of a nanolime-based consolidation treatment was investigated. Experiments were carried out in the laboratory on limestones provided by Canterbury Cathedral (England) and on archaeological limestone samples supplied by the British Museum (England), using commercial alcoholic nanolime applied with a tailored treatment process. This study shows that the performance of the treatment is affected by the pre-wetting action, the method of application, and by the retention and carbonation techniques. The treatment performance was assessed with the phenolphthalein indicator, the scanning electron microscopy–energy dispersive spectroscopy (SEM-EDS), and the drilling resistance measurement system (DRMS). Results showed that a better treatment efficiency is achieved when the following technique is observed: (a) pre-wetting the substrate with a combination of steam cleaning and ultrasonic air humidification; (b) applying the nanolime in an enclosed environment until surface saturation; (c) humidifying the treated surface with a retention pad; and (d) curing the treated substrate at 70% RH (±5%) and ~1% CO2.