Traditional stonework and pointing
Stone has been used for building in Scotland for over 5,000 years and Stirling’s architectural heritage is testimony to its durability. Understanding how traditional stonework and pointing work and how to look for some of the common problems that affect older buildings is important.
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.
The type of traditional buildings seen in Stirling feature 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.
Traditional stonework and pointing- common problems
Look for individual stones that have lost so much of their surface to decay that they now appear set back from the surrounding stones.
Loss of detail
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 cornice.
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.
Salt deposits (efflorescence)
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.
What you can do
Repair leaking or overflowing rainwater goods as soon as a problem is apparent to prevent rainwater oversaturating the stone masonry. Pointing is considered sacrificial and it will fail after a period of time. Repointing with an appropriate mortar, usually lime based, as and when the need arises will help prevent driven rainwater penetrating the core of a wall where it can cause problems such as damp on interior surfaces. Investigate the methods available for attending to stone which has failed or decayed to a point where it is creating shelves and traps for water.