Lime Mortars and there use in traditional buildings
Damage caused to stone and brick walls by Cement Pointing One of the major causes of damp in old houses is linked to the use of cement strap pointing. This became popular in the late 1960's and 1970's, when every builder was going around offering to 'repoint your walls and make them look nice'. A solid brick or stone wall, built with lime mortar, needs to breathe. It loses its moisture content through the mortar joints. If this breathability is blocked, through the use of cement, the wall immediately starts to get wet. Water is trapped, and the only way it can get out is via the brick or stone. In winter, the damp brickwork then freezes, and the familiar rotting and spalling bricks or stone start to appear. Cement pointing is responsible for dreadful damage to thousands of walls all over the country. At the same time as trapping water, it forces water into the wall - where it emerges inside - blowing plasterwork, and creating the usual symptoms of 'rising damp' - which of course, it is not! The 'timber and damp surveyor' will try to sell you yet another injected damp course, which you dont need - to prevent a problem which doesnt exist. If you have cement pointing to an old wall - the simple solution to any damp problems is to get rid of the cement. Usually, this will be all that is needed. Builders rarely if ever re-point properly, and the strap pointing usually falls off quite easily. Underneath, you will find nice, solid lime mortar that isnt damaged. If the mortar is very badly eroded, or has cracks and holes in it, then you may want to re-point using hydraulic lime mortar.
Investigate the claims made by the damp companies and building companies that you invite to 're-point' your stone or brick wall. You will be very surprised if any of them recommend using lime - most of them will want to use cement, and many of them will blame the damp problems you may be experiencing on 'rising damp' - which of course by now we know it isnt, and never was. These people just won't get the message that the solutions are so simple and cheap, that if everyone DID get the message, the timber and damp surveyors, and the chemical companies that employ them, would be out of a job. Quite often they will try to persuade you that the wall is badly damaged and needs to be 'Rendered in a Waterproof coating'. This is complete rubbish - and will destroy the wall. NEVER allow anyone to use a cement or waterproof render on any wall.
Repointing of old walls must be done using a mortar that is softer than the material we are pointing - this gives the wall the best chance of breathing. Generally, a very soft old red brick, or a crumbly sandstone or soft limestone would need what we call an NHL 2.5 hydraulic lime mortar to point it with. The joints are raked out to a depth which is equivalent to twice the width of the mortar joint - its important to make sure that we have a good depth of mortar in the joint. We show you how to do this on the lime pages of the site if you need to do it yourself - its not hard, and a good way to spend a summers day - I tell my clients to grab a few cans of beer and a chip hammer, and just chip away and have fun - it shouldnt become a chore!!
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:
Investigate the claims made by the damp companies and building companies that you invite to 're-point' your stone or brick wall. You will be very surprised if any of them recommend using lime - most of them will want to use cement, and many of them will blame the damp problems you may be experiencing on 'rising damp' - which of course by now we know it isnt, and never was. These people just won't get the message that the solutions are so simple and cheap, that if everyone DID get the message, the timber and damp surveyors, and the chemical companies that employ them, would be out of a job. Quite often they will try to persuade you that the wall is badly damaged and needs to be 'Rendered in a Waterproof coating'. This is complete rubbish - and will destroy the wall. NEVER allow anyone to use a cement or waterproof render on any wall.
Repointing of old walls must be done using a mortar that is softer than the material we are pointing - this gives the wall the best chance of breathing. Generally, a very soft old red brick, or a crumbly sandstone or soft limestone would need what we call an NHL 2.5 hydraulic lime mortar to point it with. The joints are raked out to a depth which is equivalent to twice the width of the mortar joint - its important to make sure that we have a good depth of mortar in the joint. We show you how to do this on the lime pages of the site if you need to do it yourself - its not hard, and a good way to spend a summers day - I tell my clients to grab a few cans of beer and a chip hammer, and just chip away and have fun - it shouldnt become a chore!!
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.
This stone house wall was disintegrating as a result of cement strap pointing smeared over the joints and preventing the stone from losing moisture. The problem stopped when the cement was removed and the wall allowed to breathe again. It did not even need repointing in lime mortar.
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