Building with Lime
Key Properties of Lime
Can be coloured - with a range of natural pigments
Natural protective properties - including fungal-, pest-, rot- and water- resistance
Vapour-permeable/Breathable - for excellent indoor air quality and longevity of building fabric
Off-the-shelf purchase - but specialist skills are needed, especially for lime putty
Resource Efficiency - lime mortar can be easily separated from the bricks for re-use
Listed Building Approval - often used in traditional and listed buildings
Materials and Process
Lime is produced from an abundant natural material (limestone) by burning in a kiln. In can be artisan produced in small burns, but today is largely produced in large scale commercial plants. Depending on the purity of the limestone deposit quarried, the building lime produced may be either: Air lime (pure) – which sets slowly on carbonation with the air and is stored as a lime putty under water or bagged as a dry hydrate, or a Natural Hydraulic Lime (NHL) (contaminated with other minerals) – which sets more quickly on mixing with water and is always stored bagged as a dry hydrate. Some natural hydraulic limes (feebly hydraulic limes) set with a mixture of both carbonation and reaction to water. Other types of lime can be manufactured by mixing in other minerals after burning (called pozzolans) to change the characteristics of the binder; these are called Formulated Limes (FL).
Lime is relatively high-embodied energy material, being burnt in a kiln, although compared to Portland cement (essentially a very strong formulated lime), the burn temperature is lower, and the lower density of lime compared to cement, means that energy used in transport is slightly less. As lime cures in the building, it re-absorbs some of the carbon that was released when it was burning. Air limes re-absorb the most atmospheric carbon, with a decreasing amount re-absorbed the more hydraulic a lime is.
Different Uses and Contexts
Lime has so many uses it is hard to list them all, but its main use is as a binder, and the list of what it can bind together continues to grow. Lime can be mixed with soils, sands and fibres to produce many different building materials; walling materials like bricks and blocks; mortars; plasters and renders; paints and even plant fibres to create insulation, e.g. hempcrete.
In the UK, use of limes in building was almost completely replaced by Portland cement during the 2nd half of the 20th century, but a gradual recognition of the problems with cement (lack of vapour permeability, tendency to crack, resource inefficiency, etc.) has led to a resurgence of interest in, and use of, lime mortars and plasters, both in the historic built environment, and more recently in sustainable new build.
Lime is an excellent building material. It acts as a binder to many natural building materials; mortars, renders, plasters and paints. Examples exist in the archaeological record of lime being used in mortars, floor screeds and wall coatings for many thousands of years around the world.
Because of its many different forms, lime is extremely versatile, but if you are not knowledgeable about the different types of lime, it’s best to get advice about which kind of lime product will suit your specific design and geographical location.
Choose lime for resource-efficient, healthy, sustainable new build projects and for all works in the historic built environment. Take advice from specialists on the best kind of lime to use in a particular context and consider the specialist skill level of the contractors on site, to decide whether traditional, or mix on site methods are best, or whether modern formulated lime products are more appropriate.