A study of the deteriorating external coralline limestone walls : a case study on Bighi ex-royal naval hospital East wing, Kalkara

Abstract

In this study, research was carried out in order to better understand the causes leading to the deterioration of the Coralline Limestone walls surrounding the East wing of the Ex-Royal Naval Hospital in Bighi, Kalkara. The Coralline stone blocks were observed to undergo granular disintegration, and at places, very severe back weathering. In the first part of this work, the deterioration occurring on the three walls of the building was thoroughly mapped. This was followed by a lithological study based on a visual assessment of the stone blocks and backed by historical documents that date back to the time of building of the Bighi complex. Moisture and salt analysis were carried out on limestone samples extracted at different heights along three walls of the building. A small pilot study was also carried out in order to map the prevailing wind direction around the building to assess currents that may be leading to wetting and drying cycles. Moisture analysis showed a situation of rising damp along three walls of the building. Sulphate, chloride and nitrate salts were detected within the walls of the building at all levels sampled; the concentration of the different anions generally increased with increase in height in line with the moisture flow. It was interesting to note that the wall that showed the greater deterioration was also the one exhibiting the highest concentrations of salts. This wall faces the South-East is therefore the one which experiences the more severe cycles in temperature and water content (wet-dry cycling). The wall is also located within a ditch, so localized flow of air currents within the enclosure could potentially accelerate the deterioration process by enhancing the drying process of the water from the Coralline Limestone aiding in the weathering process by salt crystallisation.