An investigation of factors affecting the durability of masonry mortar

Mortar durability in temperate climates is related to the surface hardness of the mortar joint. The Australian Masonry Structures standard AS 3700 contains a test method known as the scratch index test for measuring this hardness. The paper describes an investigation using the scratch test to explore the effect on durability of sand type, cement type, mortar composition and joint tooling. The results at 90 days age indicate that joint finish, mix proportions and sand type are significant factors affecting durability. In addition, both cement type and joint finish interact with sand type. Ironing of joints and the presence of fines in the mortar, either from a proportion of clay in the sand or from the inclusion of lime, enhance the scratch index.