Before masonry repairs are undertaken it is important to understand the principle issues affecting the stonework and the mortar joints, including any inherent defects, construction defects and problems resulting from inappropriate maintenance and repair.


Prior to carrying out stone repairs the existing stone should be assessed and categorised to establish the:


Type: ashlar, random rubble, coursed rubble etc.


Tooling: broached, stugged, polished


Joints: v-jointed, square-jointed, fine-jointed etc.


These details should be replicated, where appropriate, when stone replacement and pointing is carried out. Inappropriate replacements can affect the appearance as well as the architectural integrity of historic buildings.


It is also important to eliminate the cause of any decay by removing sources of soluble salts, preventing the concentration of moisture and rectifying any active structural faults.


Consultation with a good stonemason, or if possible petrographic analysis, will establish the composition of the stone ensuring that any repairs are compatible with the existing stone.


60 Listed Heritage Magazine January/February 2020


INDENT REPAIRS ‘Indenting’ is the term used to describe the insertion of a new stone, or piece of stone, to replace one which is damaged or decayed. Indenting may not always be necessary when a stone has a defect; if the stone can reasonably be expected to survive for another 30 years and does not present a weathering or structural problem, it should normally be left, regardless of its appearance.


Where indenting is appropriate, the stone for the indent should be selected to closely match the original stone. As with all stonemasonry, a reputable masonry contractor should be used with the relevant craft skills of sizing, cutting, tooling and setting the indent without damaging the surrounding masonry. Artificial stone should not generally be used on listed buildings.


With all new stone indents there will be a visual contrast between the colour of the old and new stones. However, this will only last for a few years before the effects of natural weathering will soften the appearance of the repair enabling it to blend in with surrounding stonework. Cosmetic ageing treatment of indented stone, either by cleaning the old stone or distressing the new, is not normally recommended.


Partial indenting (i.e. replacing a small part of a stone) should be treated with caution.


Harled and limewashed house with exposed stone margins around the windows and doors. Note the pantile roof has a slate easing course which prevented jets of water hitting passers by on a rainy day


In certain circumstances, small indents may be appropriate on moulded detailing, but leaving the damaged stonework is often an acceptable way of ensuring authenticity and more acceptable than carrying out a visually intrusive repair.


REDRESSING Redressing refers to the removal of the surface layer from a decayed stone. This is rarely if ever appropriate as it removes the historic surface and can cause damage to the underlying stone.


MORTAR REPAIRS Mortar repairs to stone (sometimes referred to as plastic repairs or dentistry repairs) should only be used as an extension of pointing to fill in small areas of decay and extend the life of a stone which would otherwise have to be replaced.


Continued >>


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