THE LIME PAGE
everything you need to know about limestone
All about the lime ,
we specialize in repointing with traditional lime mortar to restore and preserve lime built buildings here's all you need to know about lime damages of cement pointing on a lime built building.
For century's lime built buildings have been able to breath ,move and mature until the late1920s when Portland cement became readily available along with the cement came strap pointing none widely today as weather pointing. Since the arrival of cement it has taken over the construction industry and this is the one major cause for damp and damaged brickwork across London and the UK
SPALLING OF BRICKS ON A LIME BUILT BUILDING
In construction ‘spalling’ refers to the flaking, cracking, peeling, crumbling or chipping of stone or bricks, particularly where areas of the surface are said to have blown. This can occur as a result of water penetration, freezing, and then heating
Spalling can be inconsequential, that is, or it can lead to serious structural damage requiring costly repair work.
Older bricks deteriorate through spalling as a result of moisture penetration, eventually resulting in the brick crumbling.
One of the commonest causes of spalling in old, solid walled buildings is the use of cement pointing, over soft lime mortar joints. Interstitial moisture is lost primarily through the mortar joints - the lungs of the wall - and when blocked with cement, (often known as ribbon, or strap pointing) this moisture then tries to escape through the brick faces, blowing them.
Water is absorbed by the porous surface of old bricks, and in cold periods, expansion by freezing can cause them to crack. Changes in weather, humidity and temperature are a contributing factor. Minor movement in the structure can leave cracks in mortar through which moisture can penetrate. Very soft hot lime mortar will alleviate this problem, being highly porous, and it soaks up moisture, releasing it as conditions change. Other elements of the building can lead to similar problems, for instance, poorly fitted windows, gutters and downpipes that leak and damaged chimneys.
MOSTIURE & DAMP
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 don't need - to prevent a problem which doesn't exist. If you have cement pointing to an old wall - the simple solution to any damp problems is to get rid of the cement and asses your ground levels , guttering and other aspects which can cause your wall to get saturated with water depending on were these problems have arises, 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 isn't damaged. If the mortar is very badly eroded, or has cracks and holes in it, then you may want to re-point using a appropriate hydraulic lime mortar.
choosing between lime and (Portland) cement is critical and it is frankly extraordinary how often even professionals get it wrong. It’s critical because the alternatives behave so differently they cannot be interchanged and using the wrong mortar will compromise structural rigidity. Therefore, any repairs to and/or repointing of an older brick/stone building must replicate the exact formula of the original mortar.
Incidentally, both English Heritage and Historic Scotland have banned the use of cement on all historic buildings because it encourages damp and can actually bring down centuries old buildings.
DIFFERENCES BETWEEN LIME MORTER & PORTLAND CEMENT
lime mortar
Lime mortars and plasters are:
Permeable. This means that vapour can pass through them at an almost imperceptible level, which is a healthier option for inhabited buildings as it regulates humidity.
Flexible.
Stone or brick laid with lime can move as the earth moves through changing seasons, without cracking the structure or causing instability. There is no need for expansion joints.
Soft.
Plasters and mortars should not be harder/stronger than the backing surface to which they are applied.
Weatherproof. Not waterproof, thus protecting the building without sealing it.
Not susceptible to frost. They do not freeze as they are not ‘wet’, therefore do not require foundations to be below the frost line.
Do not attract moisture. They are not a ‘wet’ material, and so don’t need to be covered with a waterproof barrier in order to protect other materials around them.
Deal with moisture effectively. They can hold excess moisture from the atmosphere in humid conditions e.g. in a shower, without becoming ‘wet’ and then release it slowly back as humidity drops.
Proven over centuries. The Romans used lime very effectively for many applications including major engineering projects such as bridges, domes, suspended floors and heated floor slabs. The earliest known use of lime is 4000 years ago.
PORTLAND CEMENT
Not permeable. Creates a sealed surface that does not allow vapour passage.
Rigid. Requires expansion joints to allow for natural earth movement without cracking.
Hard. A great property in the right place but often cement is too strong for the materials it is used with.
Waterproof. Completely seals mortar joints or walls.
Susceptible to frost. Will crack in very cold conditions and therefore if used in foundations, needs to be in deep trenches that make contact with the warmth of the earth to avoid problems associated with frost heave.
Attracts moisture. Other materials around cement need to be protected from it as it holds water and can cause rot to develop.
Does not deal with moisture. Can cause condensation problems in bathrooms, kitchens, bedrooms etc. as it does not regulate moisture.
Does not have a long history. It was invented in the mid 19th century and began to be used extensively from 1930 onwards. We are seeing some major damp and durability problems now, caused by the inappropriate use of cement from 50 or so years ago e.g. collapse of cob walls re-plastered with cement, the need to re-inforce some motorway bridges, excessive cracking in town houses leading to difficulty in re-selling and costly avoidable repairs.
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