Pointing With Lime Mortars
Traditional mass-masonry wall construction (which includes most walls built before 1919) 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.
Cheshire Pointing are approved Contractors of Conserv Lime-Mortar Products
HYDRAULIC OR NON HYDRAULIC LIME
Introduction to Hydraulic and Non Hydraulic Limes
Limes when used in building can be categorised into two types, either hydraulic (Natural Hydraulic Limes) or non-hydraulic (lime putty).
Hydraulic limes set by hydrolysis, a reaction caused by water. It causes a faster and harder set, therefore these limes are more often used for exterior work, especially in exposed or damp conditions. Hydraulic limes are available as a bagged powder and in differing degrees of strength.
Non Hydraulic Limes are putties and set by carbonation. This causes a much slower set and the lime remains softer and more breathable. Our non-hydraulic lime putties are matured on site and used to produce our medium, coarse and fine set plasters and mortars.
NATURAL HYDRAULIC LIME (NHL) is produced by burning and slaking limestone which is quarried with a proportion of silica and trace elements.
It is the silica and trace elements that when burnt, become reactive with water and will cause an initial hydraulic set of the mortar when mixed with water.
It is the initial hydraulic set that makes the hydraulic lime mortars easier to use for the contact work and for conservation work where time scales and ease of use are important.
Lime putty or non-hydraulic lime is produced by slaking fresh Quicklime (lump lime) in an excess of water which is then left to mature for at least three months. The resulting fat lime putty hardens as a result of exposure to the air /re-carbonation and does not set under water.