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Natural hydraulic lime is an essential ingredient to our industry and we work closely with the Anglian Lime Centre to ensure we provide the best lime mortars available. Whether for bedding stone, repointing historic brickwork, or rendering, using the right aggregate with the correct lime will ensure both longevity and aesthetic good looks.
We use various strengths of lime mortar depending on the substrate we are pointing, as a general rule the softer the brick or stone then the weaker the strength of lime we use. Anglia Lime supply NHL (Natural Hydraulic Lime) 2.0, 3.5 up to 5.0
Certain types of limestone contain inclusions of silica. When such limestone is burnt, these naturally occurring “impurities” convert to compounds that cause the lime to set when added to water. Such lime cannot therefore be slaked to produce a lime putty, as it would simply solidify.
It is therefore slaked by spraying with a precisely metered quantity of boiling water, just sufficient to change it from quicklime (calcium oxide) to calcium hydroxide. The heat produced by the exothermic reaction that this causes is sufficient to leave the resultant lime as a dry powder, known as Natural Hydraulic Lime.
Natural Hydraulic Lime, mixed with sand and water to make a mortar, sets initially by reacting with the water (the hydraulic set) and then goes on to carbonate (combine with carbon dioxide) in the same way as a mortar made from lime putty.