Non-hydraulic lime

England in 2008, defines non-hydraulic lime (or putty lime) as: ‘Lime which will not set by chemical reaction with water but requires exposure to carbon dioxide in the air in order to harden. Unlike hydraulic limes (see Hydraulic lime), it is derived from pure limestone. It is commercially available in powder (hydrated) or putty form.’

Short Guide, Lime Mortars in Traditional Buildings, published on 1 March 2013 by Historic Scotland, defines putty lime as a: ‘Hydrated lime binder that has been slaked with an excess of water forming a wet paste that can be left to mature over time.’

Society for the Protection of Ancient Buildings (SPAB) definition online Glossary defines lime putty as: 'Calcium hydroxide (Ca(OH)2) formed as a paste when a non-hydraulic or weak (NHL 2) hydraulic lime is slaked in an excess of water and the milky suspension is allowed to settle. Can also be made by mixing hydrated lime (the form widely available in builders' merchants) and water, although this gives a less workable mix with inferior plasticity and binding properties.'

See also: Hydraulic lime.

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