Design of quality, durable mortar for the conservation of historic masonry fabrics

Abstract

The last twenty years have shown a steady increase in the number of conservation works to historic structures carried out in Ireland. Much of the repair and maintenance to historic masonry buildings have required pointing, rendering, capping and grouting with mortars. Ordinary portland cement mortars can often be incompatible with historic and traditional materials and cause both structural and aesthetic damage. There has been a move in conservation work towards the use of lime mortars making allowances for the limitations of this material (eg. seasonal work, lower durability). It is the objective of this project to produce a quality, durable mortar to repair Ardamullivan Castle, a 16th century tower house in County Clare. This mortar must be compatible with the original mortars and the adjacent masonry. To this aim, the original pointing mortar and the stone masonry were studied by means of analytical techniques and laboratory testing. Porosity, densities, compressive strength, capillary suction and water absorption were tested according to relevant standards. Analytical techniques include petrographic microscopy and X-Ray diffractometry. Based on the results of this study, the components and proportions of new repair mortars were specified and the mortars fabricated and tested in the laboratory. The porosity, densities, water absorption and compressive strength of several compatible repair mortars were measured and a repair mix selected to be used in conservation works to the Castle.