What is lime mortar?

What is lime mortar?

As a Conservation Architect working on many types and ages of building, a common subject which I am questioned about is Lime Mortar. The most common questions are:

·         What is lime mortar?

·         What’s the difference between cement and lime mortar?

·         Why use lime mortar?

·         When should I use lime mortar?

·         How to tell the difference between lime mortar and cement based mortar?

·         Can’t I just use cement mortar? Does it really matter if I use Lime?

During this and the next few blogs, I intend to answer these questions and look at the reasons for my answers, to justify what I have to say using examples and providing references for further reading where the reader wishes to look further into this interesting subject.

While you could be forgiven for thinking that this subject is rather dull? boring? Obsolete? You could not be more wrong, the more Lime mortar is understood the more fascinatingly clever and simple this natural material is. From the Romans (this may sound a little dramatic but this did all begin with them and their ancestors) through to the bricklayers of the early 20^th century, this material has been integral to the mason of either brick or stone in the erection of their structures. The flexibility multifaceted qualities and durability of this material allowed the mason to create the structures of their day, many of which survive today.

As can be seen in this photo, just because there are old bricks, the mortar isn’t always lime, this gate archway was rebuilt in cement mortar in the 1920’s.

From the early20th Century onwards, the development of cement based mortar began in gain momentum and by the mid 20^th Century lime was a material which was seen as old fashioned and cement appeared to be by fare a superior material.  This development of the use of cement and the refining of this material to make it stronger, quicker setting and more impervious to moisture  led to the skills and traditions of centuries of lime use to become forgotten and lost.

In the 1970’s the realisation that this lost art had occurred provoked the beginning of the attempt of developing this lost craft, this has been in a continuing development from then until today when there are now new and exciting realisations on how modern materials can be used to replicate the historic use of mortar. Cement has been found to be quite damaging to historic buildings and can often increase material and environmental issues within a building.

The organisations pioneering this development have been English Heritage (now called Historic England https://historicengland.org.uk/ ) and the Building Limes Forum (https://www.buildinglimesforum.org.uk/) . I would urge anyone who has an interest in educating themselves in this topic to join this pioneering organisation.

To try and keep this and the following blogs concise I will try and outline the basic issues, and will provide links for the reader to do their own further research on the subject.   

 

Thanks for reading

James