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Stone has been used for building in Scotland for over 5,000 years and Stirling’s architectural heritage is testimony to its durability. Both whinstone and sandstone are used in Stirling. These have typically been built with mass-masonry wall construction. This means there is no cavity such as that found in modern construction. They rely on the lime mortar used to build and point each stone to transport moisture which has entered the wall to the outside surface where it evaporates.
Most 18th and 19th century stone buildings were designed in a very informed way to control the flow of water over their surface. For example, the cornice and string courses below function to direct water away from the face of the building as well as being decorative.
You can find out more in the HES Inform Guide ‘Masonry Decay’ along with other publications in this series.
Look for individual stones that have lost so much of their surface to decay that they now appear set back from the surrounding stones.
Keep an eye out for a loss of moulding detail on the underside of cornices or projecting courses can leave the drip function ineffective allowing water to run down the face of the building.
Where the mortar pointing has failed there will be gaps visible between the stones. Daylight can sometimes be seen between sections of projecting cornices and into chimney flues.
Check to see if cement mortars have been used. Modern cement based mortars often appear very grey. They are hard and brittle and usually erode more slowly than the softer surrounding stone leaving the pointing mortar proud of the stone surface.
White powdery deposits on masonry surfaces are often the result of soluble salts in water passing through the stone. As the water evaporates at the surface salt crystals are formed and left behind. These deposits can indicate that an area of masonry is subject to continual wetting.
If you need work to the masonry of your building, always ensure that you appoint a contractor who is experienced in stonemasonry and the use of lime mortar. Contact the TBHC team for advice.