Comparative testing of hydraulic lime and OPC mortar mixes

In recent years there has been in increasing trend towards the use of hydraulic lime-based mortars within the construction industry, especially in low-rise domestic dwelling — due in part to their sustainable credentials. However, the construction industry has, until recent times, solely relied upon the use of Portland cement-based mortars and the introduction of lime-based mortars has added another dimension to the choice of binder and mortar specification to use. This limited comparative study is designed to clarify the relative merits of the two binder types in terms of their compressive strength, flexural strength, water absorption and porosity. The study was conducted using three different binder to aggregated designations: 1 part binder to 3 parts sand, 1 part binder to 6 parts sand and 1 part binder to 8 parts sand. The binder designations were chosen to give a range of different mortar types that are commonly used in the industry. A constant mass of aggregate was used and the proportion of ‘binder to be added’ calculated to give the desired ratios. This was done to enable greater control and consistency over the workability of each mix when adding the water.