This is the crucial point. How many times have you heard "you should use lime"?

Lime isn't a one-product-fixes-all-problems affair.

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The lime revival saw a huge push for the use of Natural Hydraulic Lime (NHL), not the least of which came from the manufacturers. Mortar specifications have been extremely generic ever since:

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NHL    2:    Internal work only

NHL   3.5:  Exterior repointing and rendering

NHL    5:   Exterior use in exposed positions

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Research is underway to better understand the properties affecting Natural Hydraulic Lime (See Historic England's Current Research). NHLs are tested under the British Standard for lime however the test for complressive strength is carried out at 28 days - appropriate for the modern mortars the test was designed for, but does not account for the compressive stregnth increases that lime undergoes in the months and years during its process of carbonation.

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The case is true of all NHLs.​

Natural hydraulic lime has its place but its use should be limited situations were the mortar is being used in damp environments or where higher compressive strengths are key to fullfilling its function.

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The conservation of historic buildings is a specialist field and it's still learning. Most of the knowledge was traditionally  handed down from person to person and a lot of it was lost during the great wars. For this reason, a substantial amount of ongoing research is being carried out using historic books and documents.

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At Russet and Sage, we strive to be at the forefront of current best practices which means constantly evolving our practices to offer our built heritage the best possible chance of survival.

 

We have been successfully using hot-mixed quicklime mortars for years and are working towards educating homeowners on its benefits over hydraulic limes and lime putty. 

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