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Richard Williams

Hot Lime Mortar Mixes

27th March 2015

Slaking quicklime on site to make hot lime mortars

The majority of lime mortars used in conservation work today are mixed from lime putty or powdered NHL, but is this what would have been used originally in construction?

There is a really good article by Gerard Lynch, called “The Myth in the Mix” on www.buildingconservation.com, which describes old textbooks and site journals expressing quantities of lime ratios in quicklime format, to be slaked on site, opposed to ready slaked Lime Putty. The point of the article is to try to explain why a 1:3 quicklime mix is similar in composition to a say 1 : 1.5 Lime Putty Mix.

So why would quicklime be used instead of Lime Putty? It is possibly due to transportation costs and storage. Lime putty contains water and is wet, quicklime is a dry and is half the volume (roughly) before slaking than the Lime Putty.

To put this in perspective I have recently undertaken a renovation project where I have used about 4 tonnes of Lime Putty , with 8 tonnes of sand, using either a 2.5:1 - 2:1 mix for most finishes. That’s 12 tonnes of material for just the renovation. How many tonnes were used in construction, 40 , maybe 60 ? If I were to slake the lime on site I could have reduced the quantity of material needed by 2 tonnes of Lime, thus by around 20%.

Delivery costs and transportation costs for me are negligible as my materials arrive on the back of a trailer pulled by my Land Rover, but when the place was built in 1840 a 20% saving in time and effort dragging tonnes of lime to the site would have been welcomed.

I will be researching Hot Lime mixes over the coming months so this it just a precursor to warm everyone up on my opening thoughts on the matter.

Richard Williams
About the author

Richard has worked on many of London's most prestigious buildings in his role as a Chartered Surveyor. 

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