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Lime Plastering Lime Plastering HISTORY AND SCIENCE IN THE MIX It’s not clear precisely how long lime plasters and renders have been in use (plaster being The art of decorative Lime putty plaster the internal coating and render the external plasterwork using lime made with fine kiln coating), but evidence can be found dating putty and gypsum dried sand back as far as approximately 4000 BC (photo courtesy of Sean when lime plaster was used in the pyramids Wheatley Plastering) of ancient Egypt. Some of the earliest documented guidance relating to the use added to appropriately sized aggregates for of lime putty plasters can be found in the renders and plasters, and sometimes mixed writings of Vitruvius, a Roman architect and with other binders or additives to give suitable engineer, who describes the basic procedures properties for a wide range of protective for making ‘stucco’ (plaster) from slaked lime and decorative applications. putty back in circa 40 BC. Vitruvius, The Ten Books on Architecture. And it was the Fine sands were selected and mixed with lime Romans who introduced the use of lime to putty for internal finishes, with coarser sands the British Isles circa 43 AD... a little behind used for thicker coats of external render the times, it might be said! (which often included the addition of animal hair for flexibility and strength). Marble dust Many of you will be familiar with the enabled rich, mature putty to be polished for fundamental benefits of lime binders over decorative plaster effects, and the gypsum- conventional materials, such as good vapour- based plaster of Paris is combined with lime permeability (breathable) and flexibility, putty for the traditional renovation and but the durability of lime plasters if often replication of decorative plasterwork and overlooked. Solid, sound examples of lime The manufacturing process for traditional cornicing. plasters and renders which are hundreds of plasters begins with calcium carbonate, in years old are commonplace in homes and the form pure limestone and seashells, APPLICATIONS FOR REPLICATION AND properties across the country – outliving which is burnt at temperatures up to 900°C CONSIDERATIONS IN RESTORATION lifespans associated with their modern to produce calcium oxide. This ‘quicklime’ is One significant benefit with traditional lime counterparts many times over! Aesthetically, then added to clean water in a process putty plasters and renders is that the type of lime plasters are also more in keeping with known as slaking and left to mature for materials and sequence of coats are generally our traditional buildings, particularly when approximately 12 weeks, resulting in calcium consistent for most applications. compared to harsh looking alternatives dihydroxide, more commonly known in this such as cement. form as lime putty. The lime putty was then Continued >> Listed Heritage Magazine November/December 2017 85 LIME PLASTERING A traditional lime 3 coat lime plaster burning kiln (personal on to timber lath protective equipment advised!) Applying this principal to lime plasters and renders may suggest the selection of a complete sympathetic replacement as it’s often difficult to repair the existing material with new coats of lime. In some instances, primers or renovation plasters can be used to make good without going to the disruption or cost of a complete replacement. However, care should be taken to ensure renovation External renders on to solid masonry Club (LPOC) and Society of the Protection materials are compatible and will not have a normally consist of a harl/scat coat, a haired of Ancient Buildings (SPAB), before seeking detrimental effect on the fabric of the building. scratch coat and an unhaired float coat (with guidance from established and reputable the addition of an extra dubbing-out scratch suppliers who offer a range of solutions, as STANDING THE TEST OF TIME coat for very uneven substrates). these are less likely to be biased towards a A wealth of information, research and shared specific product or brand. Remember that not knowledge is available at our fingertips when Internal plasters on to solid masonry are the every solution will be appropriate or available investigating construction materials and their same as for rendering but an extra top coat of to your property so speak your local building benefits specific to our own projects. But like fine lime plaster skim is normally included. control and conservation officer before any online results found on popular search committing yourself financially. engines, or views from industry ‘experts’, Variations on these fairly standardised lime there’s often a lot of inconsistency and strong plaster and render specifications can include opinion to sort through before finding the The renovation of period properties is the use of a pozzolan (a natural setting agent) right answers. If there’s any doubt then surely often required to maintain and restore our for external applications, and the omission of the achievements of ancient craft and skill that homes to their former glory. This could be the harl coat when application is directly onto have stood the test of time, whether it be an the result of failed materials due to their reed or timber lath. intricate ceiling rose, the magnificent pyramids age or from alteration to the property, or of Giza, or a Victorian lath and plaster ceiling, As with many construction materials, building possibly due to the detrimental effect of are proof enough to tell us all we need to limes have evolved in recent years and the UK inappropriate materials resulting in damp, know when considering the renovation or has seen the introduction of many pre-mixed mould or decay. Careful consideration should replacement of plasters and renders in our natural hydraulic lime and formulated lime always be taken to restore sympathetically but beautiful, traditional homes. renders which offer benefits such as improved also in doing what is necessary to maintain insulation, or the ability to be applied onto rather than replace altogether, wherever carrier boards (such as wood fibre, cork or possible. ‘Conservation repair’ is a philosophy wood wool). The sheer number of modern associated with SPAB which states that ‘the variations will undoubtedly lead to confusion only work that is unquestionably necessary Article by Ryan Stojic when researching and deciding on the best (whether it be repair, renewal or addition) Mike & Wye Associates Ltd approach to your own situation. Be sure to is that essential to a building’s survival. Old 01409 281644 make use of independent advice from industry buildings cannot be preserved by making www.mikewye.co.uk experts, such as the Listed Property Owners them new.’ 86 Listed Heritage Magazine November/December 2017.
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