Hot mix lime
Updated: May 31
On a busy conservation site in Bristol last year, putty limes and hydraulic lime mortars were the topic of conversation, and a spin off discussion over hot mix lime was sparked. The conservation project in question involved a large amount of lime repointing works, much at high level, and despite taking place in the UK's 'warmer' months, had been plagued by wet weather. This cast thoughts back to a hot lime workshop attended a few years ago at Coventry cathedral with Nigel Copsey. It was a fascinating day that opened the mind to hot lime, with a chance for everyone to get hands on - always a valuable experience for designers to fully understand what their specifying.
The day was packed full of information, recent case studies, extensive research and excellent demonstrations, one of which can be seen in the video at the bottom of this post.
On live heritage projects in the past we have tended to stay with the more familiar NHL coded limes, along with most. However, the relatively recent University of Bath studies hailed some not-so-surprising results, and huge inconsistencies with different NHL limes suppliers, which was discussed in detail on the course.
A resurgence of traditional hot mix limes in Scotland has been alive for some time, and its easy to see why it's particularly suited for use in harsher conditions with the increased technical performance over the more conventional ‘cold mortars.’ From my experience there is still apprehension in the UK by contractors and specifiers alike, likely down to a general lack of awareness and health & safety management - I'd strongly encourage anyone interested in the subject to attend a Hot Lime Workshop day to learn more.
We're always very interested to hear from anyone that has used hot limes on live projects, what their experience was like and if a full scale resurgence in the UK conservation industry might ever come about. On sensitive conservation projects its difficult to see how the information we now know hold about NHL's can be ignored for much longer.
The following link is to a great article by the IHBC for further reading; https://www.designingbuildings.co.uk/wiki/Hot-mixed_mortars:_the_new_lime_revival
This links to a booking page for the excellent Hot lime workshop for anyone interested;