The traditional building materials of lime mortars, renders, and plasters have been used for thousands of years and continued in use as one of the principal binders in traditional construction until the last century. Emerging evidence in the 1970s of the damage caused to historic buildings by the use of cement mortars and modern plasters has led to a revival in its use. One of the reasons for this is that because lime-based mortars are vapour permeable they allow buildings to ‘breathe’. This reduces the risk of trapped moisture and consequent damage to the building fabric. Lime also has a greater tolerance for movement which makes it a natural partner for stonework, cob or timber that are more susceptible to expansion and contraction.
The use of lime also has ecological benefits, in that its production creates less embodied energy than cement, its setting process absorbs CO2, and its potentially gentle binding properties enable reuse of other materials. Different limes will vary in colour and texture, and when used with a knowledge of sands and aggregates can contribute to a sense of place and local distinctiveness.
However, an understanding of working with different types of lime, as well as associated products such as plasters and limewash, is needed for effective results. Care is needed in the preparation, application and tending of these products, which is one of the reasons why it has fallen out of regular use. To address this a number of knowledgeable suppliers and practitioners have re-established this craft with whom LCA work regularly.
Pointing refers to the mortar filling the outer face of the joints of stone or brickwork. It is intended to be sacrificial, so it decays in preference to the surrounding stone or brick, and therefore requires replacement from time to time. Pointing needs to match the masonry it is working with, and if the pointing is too hard, moisture may be trapped and the stone will decay prematurely. Careful selection of mortar mix and its execution will determine the colour and texture of the pointing as well as the appearance of the wall.