Why use lime as a building material?
When it is used well, lime is undoubtebly the best and most versatile binder in the world. It has been used for thousands of years on a wide range of building projects and without question has stood the test of time.
Its characteristics can be listed as follows:
Lime mortars can protect – lime mortars and plasters have the benefit of high permeability and porosity. These characteristics allows lime to protect other adjacent materials by enabling moisture movements through the building fabric thereby protecting masonry materials from harmful salts
Lime allows old buildings to 'Breathe' – old buildings dont have modern damp proof courses so they need to be able to breathe and shed water. Newer building materials such as portland cement and gypsum plasters tend to trap water whereas lime absorbs condensation and allows the damp to evaporate out.
Old buildings move – often with shallow foundations old houses built of either timber, stone or handmade brick expand and contract with the seasons. Unlike modern cements lime can accommodate these slight movements. In fact lime is 'autogenous'. Any small cracks that appear in the lime will heal themselves over time.
Lime is soft and flexible – When you repoint or build an old wall it is important that the mortar is softer than the brick or stone. If a mortar is harder than the building fabric the substrate will be damaged before the mortar when the wall expands and contracts. Also, as water cannot evaporate through modern cement mortars it evaporates through the softer brick or stone causing spalling of the building material. Lime mortars wear out quicker than the building substrate and are therefor sacrificial. It is far easier to repoint than to have to start and replace brick or stone!
Lime is a joy to live with – Lime plasters feel cool in the summer and warm in the winter, it has a soft finish which better suits the gentle curves and contours of old buildings. Lime is also hygienic. It is a natural disinfectant and inhibits the growth of bacteria. Wood boring beetles hate it! Moreover lime finishes are very beautiful.
Lime is very durable – lasting many hundreds of years in some cases.
Lime has ecological benefits – it is burnt at lower temperatures than portland cement and absorbs carbon dioxide during the setting process of carbonation. It is therefore more environmentally friendly than modern materials.