In the UK, lime has been used as a binder in mortars and plasters since the Romans brought the technology with them 2,000 years ago.

150 years ago, Portland cement was considered a specialist’s material. However advances in industrial processes and the demand for faster building changed the market conditions and cement became the primary binder for mortars. Portland cement performs well in mass concrete and engineering structures, but where flexibility and vapour permiability are required, hydraulic limes produce superior mortars, plasters and renders.

During the last 25 years, Lime has enjoyed a steady revival for repairs to historic buildings. The soft, porous and flexible nature of lime mortars and plasters is now universally recognized as being vital to maintain the traditional breathing performance of old buildings. In addition, an increasing number of architects, engineers, surveyors and builders are now beginning to realise that lime has many benefits to offer in new construction.

The Benefits of Lime

There are sound arguments for using lime mortars in new build, relating to both performance and ecological issues. These include:-

• Using lime based mortars and plasters reduces the need for expansion / movement joints

• It uses less energy than cement to produce

• It re-absorbs some of the CO2 given off during the firing process when it sets

• It allows masonry to be recycled when the building comes to the end of its life. There would be no supplies of second hand bricks if old buildings hadn’t been built with lime

• It enables low energy, sustainable materials such as water reeds, straw, hemp, coppiced timber and clay to be used as construction materials as the lime breathes and keeps them dry

• Aesthetically, lime has contributed massively to our townscapes by enhancing the beauty of the materials used in construction.

The energy produced from non-renewable sources consumed in building services accounts for about half of the UK’s emissions of carbon dioxide (CO2). The contribution to this by the cement industry is significant. It is estimated that cement production represents around 8.3% of man-made CO2. A change from cement to hydraulic lime could therefore make a major contribution to the reduction in CO2 levels.

There has never been a better time to be using lime. There is now a British Standard BS EN 459-1 that recognises lime as a binder in its own right. The Department of Trade and Industry has invested hundreds of thousands of pounds funding research into the future of hydraulic limes in the building industry. This has provided vital information showing that hydraulic lime produces mortars which are more durable than cement based mortars and which have greater resistance to the effects of frost and salt action. This research has led to the publication of a ‘Best Practice Guide’ for hydraulic limes and a technical note to complement BS 5628 is on the way.