Why use lime ?
Why use lime and not cement
Lime mortar pointing is generally softer and more flexible than Portland cement or masonry cement and it’s better for buildings and the environment. It allows your home to breathe more naturally than cement finishes, it can help with damp problems and it will also enable your home to move naturally without cracking walls or bricks. Mortar finishes should always be softer than the bricks or stone to enable this to happen and lime mortar provides just such a solution.
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Traditional mass-masonry wall construction (which includes most walls built before the 1920's) works on the basis that moisture entering a wall is able to escape as water and water vapour as easily as possible. Lime mortars can readily handle the transmission of water and water vapour between the inside and outside of a masonry wall, owing to the complex interconnected pore structure of masonry.
The use of cement mortars is widely recognised as being detrimental to such buildings and structures as they can drastically alter the way in which a wall handles water and water vapour. Cement mortars tend to have a consistent and 'closed' pore structure that traps water rather than allowing the building to breathe (not necessarily a problem in modern cavity wall construction). Any trapped moisture will expand if subjected to freezing conditions, and mortars may ultimately fail, often causing damage to the surrounding masonry in the process.
Masonry walls need to be maintained and repaired, just as roofs and rainwater goods do. Where walls are solid, without a cavity, keeping them in good repair is necessary for the interior to remain functional and dry. Pointing is the most common repair, and often one of the most poorly executed.
The two main reasons for lime-pointing repairs are:
The original lime pointing has decayed over time and needs to be replaced. This may be the result of gradual decay through weathering, or failure as a result of poor maintenance. Blocked gutters or overflow pipes, for example, lead to damp masonry and can result in frost damage.
The masonry has been re-pointed with a cement-based (or other inappropriate) mortar at an earlier date, which is causing problems to the building and/or the adjacent masonry and must be replaced with a more appropriate mortar.