The mortars of Coliemore harbour: comparison with other 19th century mortars of harbours and fortifications in Dublin Bay

Abstract

This paper investigates the mortars used to build Coliemore harbour in 1869: their materials, sources, technology and current condition. It compares their composition with other Dublin harbours and fortifications in Dublin Bay including Howth harbour (1813); Dún Laoghaire harbour (1817-1842) and Martello towers (early 19th century). All the mortars were made with eminently hydraulic limes and local sand. The original binders of Coliemore and Dún Laoghaire and the Martello towers are similar, consisting of carbonated lime and cementing hydrates with abundant iron oxides and opaques. However, the Howth harbour mortars are different: their binder, an eminently-hydraulic Lias lime, largely consists of cementing hydrates with scarce iron oxides and some calcium silicates (pyroxene). Coliemore harbour was built with local granite quarried in the Dalkey hill, bound with mortars made with hydraulic lime and local sand. The harbour fabric is in good condition, and several generations of hydraulic mortars are evident. Their physical properties are comparable to other eminently hydraulic mixes made hydraulic lime, Roman cement and Portland cement. Despite their strong exposure, the mortars remain cohesive, with absorption/porosity comparable to other eminently hydraulic materials. Occasionally, biodeterioration is strong, blocking pores, hence some porosity values are slightly underestimated. Modal percentages indicate proportions of 2: 1 (sand: binder), consistent with traditional and historic mortars. Siliceous sand consisting of granite and quartz predominate, and limestone generally accounts for 15- 20% of the total sand.