The conservation of 'Deffun' roof mortar

Abstract

Deffun roof mortars are a major element in the traditional buildings of Maltese rural and urban architecture. The conservation of these Deffun mortars is of importance to our cultural heritage. However, improper methods and materials used can accelerate the deterioration processes. The aim of this research was to understand the deterioration mechanisms of Deffun mortars and the methods that have been used to manufacture and restore them in order to find appropriate methods for their conservation. Initially, the historic context of Deffun mortars was studied. This includes manufacturing methods, other uses of the material and the origin of the technique. A review of traditional buildings was carried out. Detailed documentation of the structures and of the slopes of six traditional roofs covered with Deffun mortar was compiled and discussed. Water run off and storage systems were also discussed. Weathering and environmental factors contributing to the deterioration of mortars were examined and primary causes identified. Field interviews were also compiled to understand past and present roof interventions. This data does not only give relevant information on the materials and techniques used for repairs and maintenance but also indicate other materials and techniques used which can also contribute to the deterioration of Deffun mortar. The above-mentioned research of Deffun roof mortars was vital for a better understanding of the subject and provided the basis for the next step, which was laboratory testing of different mortars for the conservation/restoration of lacunae in traditional roofs. Seven mortar mixes were prepared and tested for strength, shrinkage and adhesion in laboratory conditions to identify the best possible mix. The results from the tests carried out indicated two mixes (mix 1 composed of slaked lime and crushed pottery and mix 7-a proprietary mix) with suitable properties to be used for filling lacunae in Deffun mortars.