Characterization and Assessment of Performance of Innovative Lime Mortars for Conservation of Building Heritage: Paimogo’s Fort, a Case Study

Along the Portuguese coastline, several military fortifications were built with the intention to protect the territory from the constant military threat from the sea. These constructions have been subjected, during centuries, to a very aggressive environment; the renders, whose main function is the protection of walls, are particularly exposed to such actions. Nossa Senhora dos Anjos de Paimogo’s Fort, better known as the Paimogo’s Fort, is one of these fortifications, built in 1674 and classified of public interest since 1957. Within the scope of the “Coast Memory Fort” Project of EEA Grants Culture Programme 2014–2021, promoted by the Municipality of Lourinhã, repair mortars are being developed for the preservation of the Fort, considering the physical–mechanical and chemical characteristics of the pre-existing mortars and of the substrate, as well as the aggressive environmental conditions. In this work, several mortar compositions, compatible with the original mortars and designed to resist the aggressive environment, are briefly described and their main physical and mechanical characteristics are analysed and compared in successive ages. Different binder mixes were used, and a fine-tuning of the aggregate was carried out. Assessment of sequential wetting/drying cycles’ effect on the mortar’s behaviour is also presented. The laboratory results reveal that mortars with additions of 30% of quicklime present the best behaviour (with the lowest water absorption and highest strength). Moreover, the substitution of part of the siliceous sand by limestone aggregate, in general, increases the mortars’ mechanical strength; however, the drying occurs slower, which could compromise the durability of these mortars if a good balance is not achieved.