26 Michael Farey discusses the pros and cons of hydraulic lime and lime mortars THEREISMORE TO LIMEMORTAR THAN ... Most, if not all, local government Conservation Officers realise the importance of lime mortars in the correct repair of old buildings. Indeed it is they, more than any other group, who have been responsible for the revival in the use of lime mortars. But do they realise the importance of what has been achieved so far, or indeed where it is leading the building industry as a whole? Various other factors resulting from developing national and international policies related to the environment are continuing the push towards greater use oflime mortars for general building work. Since the Second World War, Britain has seen irreparable damage to its stock of old buildings and a huge waste of masonry in new ones. The widespread use of Portland cement for repointing and render caused, extensive spoiling of masonry, cracking, widespread problems of moisture trapped in walls owing to the failure of Portland cement joints and the inability of render to breath. When the useful life of new buildings, particularly in the commercial sector, comes to an end, despite construction in high-quality material, the masonry has to be crushed for hardcore. In some cases, for example supermarkets, this can happen as soon as 20 years after the buildings are erected whereas the life of masonry can be measured in hundreds of years. In previous centuries masonry was recycled time and time again. Present mortars create not only waste of the early resources but a huge unnecessary addition to CO2 emissions. As a result, the movement so carefully nurtured by Conservation Officers in recent years has implications far beyond the protection of ancient buildings. The term conservation has become synonymous with the need for conservation in every aspect of the building industry. Recycling of masonry materials is only one aspect - heat conservation, reduced maintenance, increased life of masonry materials and reduced energy _consumption during manufacture are all benefits accruing from the use of lime mortars. Understanding and quantifying these advantages is occupying the thoughts and research activities of an increasing range of professionals and research authorities. Conservation Officers are under an obligation to continue and broaden their scope of influence. At present, they are in a unique position to develop the direction that the construction industry pursues. Unfortunately, theextentoftheUK's restoration and conservation activity has highlighted a major deficiency of skills which, if it remains unaddressed, may put the whole process into reverse. Many contractors have become involved in work which, because of lack of knowledge, they underprice (especially in a period of recession) and fail to carry out effectively. Furthermore the lack of understanding of what they are doing also means they fail to appreciate the importance of the work in hand. This problem can be redressed by adequate training, a system of suitable certification and the introduction of lime materials which are more user friendly. English Heritage seems likely to close the Fort Brockhurst Training Centre, leaving a gap in objective and independent training. No-one seems very keen to fill the gap. The responsibility has always rested with central and local governments to ensure that universities and colleges train students adequately. While still alive, Fort Brockhurst does provide a system of certification worthy of merit. In addition, various conservation courses within the educational system provide some skills, but these are often incomplete. Meanwhile, the majority of the construction industry, including architects and surveyors, still receives inadequate formal training on techniques and applications of lime mortars. Quite apart from the skill shortage, the other factor working against the general use of lime mortars is cost. An argument exists for suggesting that, despite the considerable increase in building costs associated with the use of high-calcium lime putties, the longterm benefits to owners justify their use. However, many enlightened professionals within the industry doubt the validity of this argument. The solution rests with the application of lower-calcium quick-setting hydraulic limes which are supplied in hydrated form, permitting the use of on-site techniques very similar to those used with Portland cement -which the construction industry understands and which do not have the labour-cost penalties of high-calcium limes. Of course, in their own interests, manufacturers of putty may argue that hydraulic lime is cement and, as such, has many of the undesirable characteristics of that material. This is not true. The chemistry of hydraulic lime is very different from that of Portland cement, as are many of the physical characteristics. Fore example, bulk for bulk (called bulk density) cement weighs twice as much as lime. This results in significant differences in the material's ability to breath and also their thermal insulating properties. Further research is required, much underway already, but what is clear is that good hydraulic limes have the desirable attributes of lime while avoiding the undesirable features of Portland cement. Despite these clear indications a fog still persists regarding hydraulic lime which, while understandable, is quite unnecessary. It provides opportunities for inexperienced as well as experienced contractors (because of ease of use) to reduce labour costs. In addition, provided that a lime is selected which does not achieve too much strength after 12 months, it will CONTEXT 52
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