Assessing the condition of limestone in a marine environment : the Qolla l-Bajda battery, Gozo : a case study

Abstract

Most heritage buildings in Malta are made of the porous limestone and some are undergoing severe deterioration due to their intrinsic properties acting together with external factors including the aggressive marine environment. Many tools, both invasive and non-invasive, exist today which can help a professional in building conservation to assess the condition of its building materials, for documentation and before an intervention is planned. The limestone deterioration of the Qolla l-Bajda Battery in Żebbuġ, Gozo, located on the seashore, is used as a case study to define a preferred methodology. A multidisciplinary approach that includes non-invasive and micro-invasive techniques and gives both qualitative and quantitative information was adopted. Documentation, in the form of illustrated glossaries, lithology mapping and mapping of the deterioration forms, was produced, representing the current external condition. The USB microscope, which is simple to use, fully portable and works at low magnifications, was found to be an indispensable tool which not only can help identify possible causes of deterioration such as biological organisms on-site, which otherwise requires sampling to be examined in a laboratory, but is also effective in reducing the number of samples when these are essential, by first allowing to identify differences in the samples’ microscopic characteristics and then for sampling choices to be made. The Salt Strip test allowed for determination of important salt ions, and the RILEM Tube test gave indications of possible saturated stones and/or different stones that are weathering differently possibly forming “crusts”. Mortar analyses, performed in a very basic laboratory set-up and assisted by a USB microscope, proved essential not only for the detection of lime-based mortars, which can be very helpful when repair mortars are being prepared, but also in identifying cement mortars which can be causing damage. This methodology, as applied to the case study, can potentially be applied to other similar structures in the local scenario to help set up an appropriate conservation plan with the intention of safeguarding these buildings not only as works of art but also as common cultural heritage.