Lime Rendering: How & Why We Use It
Traditional stone or brick buildings must be protected from the elements. This is done by applying a render. Cement render is a commonly used material for plastering stone buildings, however, it isn’t necessarily the most effective. When cement products are used for rendering bricks, cracks are more likely to develop as cement finds it hard to move without cracking.
Cement render also causes localised moisture due to its lack of breathability. Moisture can become trapped in brickwork, causing the masonry to erode.
Lime render, however, is porous. This allows the bricks to breathe and any moisture to evaporate. Lime is also resistant to cracking due to its unique “movability”. Some are surprised to learn that lime render isn’t a new idea. In fact, lime mortars and plasters have been used in construction for thousands of years. And today, it remains an invaluable resource due to its flexibility, resistance to cracking and ability to release moisture. Period buildings built with lime were designed with the knowledge that lime can move without breaking. Step foundation-footings just 400mm below ground are a common feature of these buildings, as they were designed to move with the land.
The process of rendering with lime is simple and failed renders may be effectively repaired and restored with a lime render, making total re-rendering unnecessary. The only preparation needed is removing old, decayed or hollow render, and then brushing away any loose debris. Mixing one part of lime to two and a half to three parts of sand creates a lime render. The consistency should be thick enough to stay put but thin enough to apply smoothly. The wall is then wetted to control potential shrinking and the lime render applied gradually with a trowel, in thin coats that never exceed half an inch. Lime render is normally applied in two or three coats. Even single coat work can be found in early structures and vernacular buildings.
Lime has a much lower carbon footprint than cement and it is far more compatible with period buildings than its cement counterpart.If you have any questions about lime rendering, the team at Ernest Barnes Ltd will be more than happy to help. Get in touch today!