Traditional mortars of the Fort of Paimogo: composition, performance, replication

Traditional mortars of the Fort of Paimogo: composition, performance, replication

The project "Coastal Memory Fort" promoted by Lourinhã Municipality, aims to safeguard and revitalize the Paimogo Fort.

Within the scope of the “Coast Memory Fort of Paimogo” project, the preservation of the Fort building is foreseen, respecting the authenticity of the monument and preserving the memories of the construction. In this sense, one of the first tasks carried out was an assessment of the conservation condition of the Fort building and an analysis of the original materials.

Under the current wall and ceiling coverings, which result from a recent intervention, the old masonry walls, made with stone from local quarries and lime baked in the artisanal ovens of the region, were found, as well as ceilings of solid ceramic brick vaults; traces of the original wall coverings were also identified. The LNEC team members collected samples of these mortars and analysed them, as well as samples of the ground floor laying mortars provided by the team of archaeologists who carried out the survey of the monument's structures. These mortar samples were subjected to a battery of mineralogical, chemical, microstructural, physical and mechanical tests, which allowed the determination of their compositions, namely of the coating, joints and floor laying mortars: in all cases, they are mortars of air lime and sand of siliceous and limestone nature, with varying proportions, depending on the type of mortar, between 1:1.5 and 1:4 (lime: aggregate mass proportions). Some particular features were identified: the mortars are much richer in lime than is usual in other types of old constructions or even in current conservation works; the aggregate is free of clay; and high mechanical strengths were determined in all mortars, in the range 2.5 to 5 MPa in compression, contrasting with the values ​​obtained in more recent air lime mortars.

Based on the compositions and characteristics obtained for the original mortars and taking into account the raw materials of the region, mortar formulations based on air lime are being tested for application in conservation works. Their performance and durability are in the process of evaluation in laboratory and in exposure to local climatic conditions.

See in the slideshow below, some images of the assessment of the state of conservation of the Fort and the analysis of the original materials.