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07 May 2019

Fred and Ginger, Batman and Robin, Morecombe and Wise…all famous double acts that would simply not be the same without each other. To this list we could add ‘bricks and mortar’, signifying strength and durability. It’s probably the brick that we associate most with the dependability (he’s a brick’ we might say of a ‘solid’ friend) But what is a brick without mortar? Roma Agrawal in her book ‘Build’ describes mortar as the ‘glue’ that holds the bricks - the building blocks - together, and what use would they be as a building material without it?

From the Latin ‘mortarium’ meaning ‘crushed’, many different combinations of substances have been used over the centuries to make mortar. The Egyptians used gypsum, later adding lime to make it stronger. Lime mortar was used in the construction of the Tower of London which at over 900 years old, stands testament to its durability. The Romans believed that animal blood gave their mortar greater resilience to frost and when constructing the Great Wall, the Chinese added sticky rice to their recipe in order to give it more flexibility. The majestic dome of the Taj Mahal is held together with a mixture of burnt lime, ground shells, marble dust, gum, fruit juice and egg white, collectively known as ‘chuna’.

In more recent times, mortar has been traditionally made from a mixture of sand, a binder and water. The most common binder since the early twentieth century has been Portland Cement, although the ancient binder, lime, beloved of previous generations for its strength enhancing properties, is still used in some new construction. The proportions of sand and cement are crucial to making a mortar that will stand the test of time. Too much cement and the mortar will be strong but brittle, whereas too much sand will make a mortar that is powdery and crumbles within the joints. Weak, poor quality mortar is less weather resistant and may put the building at risk of structural instability. The state of the mortar is, therefore, a factor to be assessed in a structural survey and any defect will be picked up by the trained eye of the structural engineer.