Our latest guest article from Under One Roof is full of useful information about stone repairs and preservation:
Preserving the architectural heritage of Scotland’s tenement buildings requires a proactive approach to repairs. Understanding owners’ legal responsibilities, using the right materials, and seeking professional help when needed can ensure older stone tenements stay standing strong.
Over time, the stone walls of older tenement buildings are prone to decay, so it’s important to keep them well-maintained and avoid repair methods that can cause further damage.
Who is responsible for external wall repairs?
As with any tenement repair, it’s essential to first refer to the property’s title deeds to determine responsibility. Title deeds outline the building’s rules and owners’ maintenance obligations. If the title deeds do not state who is responsible, then it’s necessary to refer to the Tenements (Scotland) Act 2004.
Under the Act, external walls are a common responsibility. Every flat owner in a tenement building has a duty to maintain the parts of the building that provide support and shelter, which includes the external walls.
Types of stone
Older tenement buildings were often built using stone, such as sandstone or granite. Sandstone, the softest type of building stone, is susceptible to weathering and easily absorbs water. This contrasts with granite, which is hard, more durable, and does not absorb water as easily. Although advantageous overall, this means if there are cracks in granite, rain can get through and run directly into the building.
Identifying the specific stone used in a tenement building’s construction is crucial for ensuring the use of repair materials that are tailored to its characteristics.
Caring for stone: the problems and pitfalls
Stone’s unique properties, such as its ‘breathability’, must be carefully considered during repair work. ‘Breathability’ refers to how stone can naturally absorb water and dry out. When carrying out repairs, such as repointing or sealing a crack, it’s essential to use materials which cater to this characteristic.
In the past, ‘plastic repairs’ using cement mortar were often used to repair stone. Cement has also been used to repoint stone. However, most of these repairs are now cracking and in need of replacement. Cement is usually hard and impermeable, so moisture becomes trapped in the stone where it can then freeze and expand. The stone can no longer ‘breathe’ and becomes damaged, as does the cement mortar, and this can lead to stone decay.
Stone will naturally age and decay overtime, requiring repair. However, using the correct materials is essential to help preserve the stone and prevent further damage.
Using the correct materials
For repointing stone, the best material to use is a lime mortar that uses the best match of sand or aggregate in colour and coarseness to the original. A stone masonry firm should be able to advise on which lime mortar would be a good match.
When it comes to repairing the stone itself, this depends on the type of repair. For addressing damage resulting from previous ‘plastic repairs’, it’s most effective to use natural hydraulic lime mortar. This material allows the stone to ‘breathe’.
If the damage to the stone is substantial and exceeds 40mm in depth, it may require removal and replacement with a new piece that matches the original using stainless steel dowels.
Getting professional help
For repairs or structural assessments involving stone, we recommend consulting with qualified surveyors or architects. These professionals can diagnose the cause of the problem and specify appropriate repair methods and materials. If there are smaller areas of disrepair, it’s recommended to use a specialist firm with experience in this type of work, such as a stonemason.
For more information on taking care of external stone walls, check out this article on the Under One Roof website. When organising common repairs, it’s important to follow proper procedures. Check out this guide to learn more.
Under One Roof is Scotland’s only charity committed to providing free and impartial information to landlords, owner-occupiers, and housing professionals on tenement maintenance and repair management.
