The benefits of Lime
Lime has long been used in construction: the ancient Egyptians used lime in the construction of the pyramids back in 4000BC, and the first historical reference to lime was in Ten Books of Architecture by Vitruvius, in the first century BC.
Known for its ability to let structures ‘breathe’, lime is made by firing calcium carbonate (limestone) in kilns to remove the carbon dioxide. The resulting calcium oxide (quick lime) can be ground into powder. By adding water, it becomes calcium hydroxide (hydrated lime). Depending on the amount of water used, this will create either a dry material or lime putty.
Mortar can be made from either form of hydrated lime, or quick lime. The lime then carbonates (reacts with carbon dioxide in the air) to bind the mortar into a hard material. Quick-lime or slaked lime can be used to bind washes, renders, plasters and mortars.
However, after the First World War, and the advent of cavity wall construction rather than solid wall construction, there was a move towards using other materials in construction such as Portland Cement and gypsum plaster, due to quicker setting times and lack of after-care required.
While these materials have their place, if used incorrectly or on old buildings, they can exacerbate damp rather than solving the problem. Portland cement is harder than lime, and can be too impermeable to use in many historic buildings. As such, it’s important to ensure you use the appropriate materials for your home rather than taking a ‘one-size-fits-all’ approach.
Lime is currently coming back in vogue, with the rise of eco-building and sustainable construction, along with the advent of new materials such as hempcrete walling, which is made with lime.
SPAB (The Society for the Protection of Ancient Buildings) runs courses in association with the Building Limes Forum, to help raise awareness of the benefits and potential of lime. In addition to breathability, which helps control moisture and dampness, lime also weathers well and has a warm colour that can add character to your home.
While lime can be a great material to use, it can still be vulnerable to salts. Restoration UK’s Mystolene PS helps avoid this problem. It’s an ionic wax emulsion plaster additive and salt inhibitor that’s been specially formulated for restoration plasterwork.
Mystolene PS is the only paraffin wax based render additive on the market. It repels water but will still allow walls to breathe and dry without allowing the salts to pass. It can also be added to Limelight Backing plaster, and is the product of choice for most professional plasterers in the restoration industry. To use, mix 1 litre of Mystolene PS with 29 litres of water. When replastering with lime, use Mystolene PS in a 6:1:1 mix (Sand/Lime/Cement).
Whether you have a heritage home or a new build, we can advise you as to the best materials for the job.