The revival of interest in non-hydraulic lime putty which received its main stimulus from building conservation and especially the great 'West Front' projects at Wells and Exeter in the 1970s was not generally extended to hydraulic limes. We have largely deprived ourselves for some 50 years of a range of traditional 'setting' limes which were once the backbone of masonry construction. Any treatise on mortar since the work of John Smeaton in the mid 18th century and until the 1950s, recognises the important role of hydraulic limes in the context of mortar and plaster. For certain types of work, these limes were the most appropriate material. Study of pre-war texts on lime and cements is to be highly recommended as an antidote to some of the 'all or nothing' modern attitudes to lime and cement, especially when supported by site observation as a way of understanding the nature and use of hydraulic limes.
Lime is the traditional, ancient binding medium of masonry.
Until the advent of artificial cements and especially the advent of Portland cement, lime was used almost exclusively and it has never entirely disappeared. Their hydraulic characteristic is produced by 'impurities' of silica and clay in the limestone from which they are burnt. Such limes need to be slaked with enough water to convert the quicklime to calcium hydroxide, but not so much that a chemical set begins. Burning and slaking procedures are thus more complex than those associated with the production of chalk or other 'pure' limes, but the materials produced are far more versatile. Under the general classification of 'hydraulic' are subdivisions suggested by Vicat and later generally adopted.