What Is Lime Pointing?
Pointing is the process of finishing off the external joints in stone or brick walls. Re-pointing is where the joints are raked out and the pointing mortar is replaced. This is due to age and doesn’t suggest there is a problem with the building. Lime mortar is meant to be sacrificial. Only hand-tools should be used as power tools will damage soft sandstone and the overall appearance of the re-pointing will be unpleasant.
Even if a wall is to be harled (rendered) pointing should be in good condition to prevent any voids within the structure which may allow ponding moisture.
Where a non-porous material, such as cement, is used for pointing, the wall’s ability to deal with moisture is severely diminished. Not only will cement look dreadful when used with stone (see examples below), it will not allow moisture to escape and, as the stone becomes saturated during rain (a frequent occurrence in Scotland) when that moisture freezes, it will expand and cause the face of the stone to spall, sometimes leading to quite severe failures (as can be seen above).
This is usually remedied by your builder (his knowledge of traditional construction possibly limited) recommending a cement repair, thus making the building even less breathable, more liable to internal damp problems and the guaranteed failure of the cement patch in a few years, to be followed by even more cement or even wholesale cement render as an ultimate ‘fix’.
It is understandable that owners then search for damp specialists to offer solutions but these solutions WILL NOT WORK.
Cement pointing leads to cement patching wihch leads to blaming the chimney for dampness which in turn leads to the loss of character and value which can cause structural problems and water ingress. Proper maintenance with an understanding of the way traditional buildings work is essential.
Lime Harling
Harling is the throwing, casting or ‘hurling’ a mix of a lime mortar and small granite chips to a prepared wall surface to create a wearing surface which protects the wall below and encourages moisture absorption from within the structure.
The application of limewash to the finish binds with the lime harling and creates a breathable (vapour permeable) homogeneous coating. This, if prepared and applied correctly, will wear gently and not fail like cement does.
The use of cements and impervious masonry paints seal the structure and remove its ability to allow the escape of moisture by evaporation. The moisture must go somewhere therefore increased moisture levels result inside, at chimney flues, in line with blocked fireplaces and where timber is built into or touches the damp wall. Where timber is in contact with high moisture levels, this can lead to decay and increased likelihood of woodworm infestation.
Most stone that our old buildings were built with was not designed to be seen. It was intended to be covered in a decorative and protective lime harling. Blame the Victorians for their need for ‘honesty’ and ornamentation in construction – together with the later invention of photography – which has instilled in our psyche a vision of bare, pointed wall structures throughout our towns and cities. Unless the stonework is fine or decorative in some way, it was likely meant to be lime harled.
Yellow house
Yellow ochre limewash over lime render
The soft, creamy glow from a lime harling is only matched in its beauty by the way it manages to deal with moisture in the building. The lime acts a poultice, drawing out moisture and allowing it to evaporate.
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