How to look after Sandstone Walls
How to look after Sandstone Walls
In Scotland, our homes and historic buildings often boast the timeless beauty of sandstone walls. From ancient castles of the Highlands to elegant townhouses in Edinburgh, sandstone has been a cornerstone of Scottish architecture for centuries. But with our famously unpredictable weather – think rain, wind, and frost – looking after these walls isn’t just about keeping them looking bonnie; it’s about preserving a piece of our heritage.
To keep sandstone walls looking their best and ensure they stand the test of time, proper maintenance is essential. This guide will walk you through everything you need to know about caring for sandstone walls.
What is Sandstone?
Sandstone is a type of sedimentary rock composed mainly of sand-sized mineral particles or rock fragments.
Simply put, sandstone is made up of grains of sand that have been naturally cemented together over thousands, if not millions, of years. This process happens under the earth’s surface where sand gets compressed and bonded by minerals like silica or calcium carbonate, turning loose grains into solid stone.
It’s a popular building material due to its durability and natural beauty. In Scotland, Sandstone has been used for centuries in constructing everything in Scotland – From grand castles to cottages.
Characteristics of Scottish Sandstone Walls
Scottish sandstone is unique in its composition and appearance. Locally sourced from quarries across the country, it often has a warm, earthy colour palette, ranging from pale yellows and reds to deep browns. This variety adds aesthetic appeal of buildings and walls made from Scottish sandstone.
However, sandstone is also porous, meaning it can absorb water. This characteristic, combined with Scotland’s wet and often harsh climate, makes sandstone particularly vulnerable to weathering and biological growth. Over time, these elements can cause the stone to deteriorate if not properly maintained.
Climate's Impact on Sandstone Walls
Scotland’s climate, known for its frequent rain, high humidity, and occasional harsh winters, has a significant impact on sandstone walls. While this weather contributes to lush, green landscapes we love, it also poses challenges for maintaining integrity and appearance of sandstone structures.
One of the primary concerns is the constant exposure to –
Rain and Moisture
Over time, this can lead to a range of issues:
Water Infiltration: Water can seep into stone, causing it to weaken and deteriorate. This is particularly problematic during winter when water can freeze, expand, and cause stone to crack.
Staining: Rainwater can carry dirt and pollutants, which may leave unsightly stains on surface of the sandstone.
Biological Growth: Damp conditions are ideal for moss, algae, and lichen to thrive. While some people find these growths charming, they can cause damage by trapping moisture against stone.
Wind and Erosion
Scotland’s windy conditions can also contribute to wear and tear of sandstone walls:
Erosion: Wind-driven rain and airborne particles can gradually erode surface of sandstone, making it rough and more susceptible to further weathering.
Debris Impact: Strong winds can carry debris that may hit and damage sandstone surface, leading to chips and cracks.
Temperature Fluctuations
Scotland’s climate can swing from mild and sunny to freezing temperatures, sometimes within a short period. These fluctuations can have a detrimental effect on sandstone:
Freeze-Thaw Cycle: When water within sandstone freezes, it expands, putting pressure on stone and causing it to crack. Repeated cycles of freezing and thawing can lead to significant damage over time.
Thermal Stress: Rapid temperature changes can cause stone to expand and contract, leading to further cracking and structural stress.
Common Issues with Sandstone Walls
Like anything exposed to time and weather, they encounter their share of problems.
Here are some common issues you might notice with sandstone walls:
1. Cracking:
What It Looks Like: Small fissures or larger cracks running through stone.
Why It Happens: This can be due to the freeze-thaw cycle, where water enters the stone, freezes, expands, and then thaws, repeating this process until the stone can’t take the pressure anymore. Structural movement or settling of the building can also cause cracks.
2. Erosion:
What It Looks Like: Surface of stone looks worn away, details are less defined, or you might see a sandy residue at the base of the wall.
Why It Happens: Wind, rain, and even the natural acidity in rainwater can slowly eat away at the stone’s surface. Pollution can accelerate this process.
3. Discolouration:
What It Looks Like: Patches of different colours, often darker or stained areas.
Why It Happens: This could be from pollution, biological growth like algae or lichen, or even from metal elements like iron fixtures rusting and running onto the stone.
4. Efflorescence:
What It Looks Like: White, powdery substance on surface of the stone.
Why It Happens: Salts from within stone or from mortar joints get carried to the surface by water. When water evaporates, these salts crystallise, creating this white powder. While mostly cosmetic, it can indicate moisture issues.
5. Spalling:
What It Looks Like: Layers of the stone flaking or peeling off.
Why It Happens: Often a result of water infiltration combined with freezing temperatures. The surface layer of stone detaches because the expansion of freezing water pushes it outward.
6. Biological Growth:
What It Looks Like: Green, black, red, or even yellow patches or layers on stone.
Why It Happens: Moss, lichen, and algae thrive in Scotland’s damp conditions. They can hold moisture against the stone, leading to further decay, and some organisms produce acids that can dissolve stone’s minerals.
7. Mortar Deterioration:
What It Looks Like: Mortar between stones crumbling or missing.
Why It Happens: Mortar can be softer than sandstone and thus erodes faster due to weather exposure or might not be suited to the local climate conditions.
8. Rising Damp:
What It Looks Like: A ‘tide mark’ on the wall, often with peeling paint or wallpaper inside, and possibly efflorescence or mould outside.
Why It Happens: Groundwater rises through the stone due to capillary action, bringing salts and moisture that can damage both – stone and any interior decorations.
Professional Soft Washing Techniques
Why Soft Washing Is Ideal for Sandstone
Soft washing uses low-pressure water combined with specialised cleaning solutions. It’s effective at removing dirt and biological growth without damaging the delicate surface of the stone.
Using DOFF Steam Cleaners for Effective Cleaning
Specialised Cleaning Products
Using HF Acid-Based Products Safely
Alternatives for Specific Staining Issues
Routine Maintenance Tips
Inspection
How Often: Check your walls at least twice a year, ideally in spring and autumn. This helps you catch any issues before they turn into bigger problems with the change of seasons.
What to Look For:
Cracks or Chips: Small cracks can become big ones if water gets in and freezes.
Flaking: If the surface is flaking off, it might need some attention to prevent further deterioration.
Look out for moss, lichen, or any plant life. While they might add a touch of green, they can hold moisture against the stone, which isn’t good in the long run.
Cleaning
Be Gentle: Sandstone is softer than you might think. Avoid using high-pressure washes which can erode the stone.
Cleaning Agents: If you need more than water, choose a mild detergent. There are special stone cleaners available, but make sure they’re suitable for sandstone. Always test on a small, hidden area first.
Rinse Thoroughly: After cleaning, rinse with clean water to ensure no soap or cleaner residue is left.
Avoid Salt: If you’re near the coast or use de-icing salts in winter, be aware that salt can damage sandstone. Try to use alternatives where possible.
Advanced Care and Restoration
Professional Assessment
When to Call the Experts: If you notice large cracks, significant stone decay, or if parts of the wall seem unstable, it’s wise to get a professional opinion. Heritage specialists or structural engineers with experience in stone conservation can provide a detailed assessment.
What They’ll Do: They’ll look at the overall condition, possibly using tools like wall inspection cameras for internal checks or drones for high or hard-to-reach areas. They can tell you if the issues are cosmetic or structural.
Repair Techniques
Consolidation: For sandstone that’s starting to crumble or powder, consolidants can be applied. These are chemicals that penetrate stone and harden to restore its strength. However, this should be done with caution and ideally by professionals, as the wrong product can do more harm than good.
Pointing: Removing deteriorated mortar and replacing it with new mortar can prevent water infiltration and structural damage. It’s important that new pointing is done carefully to avoid damaging the surrounding stone.
Stone Replacement: When a stone is beyond repair, it might need replacing. The key here is to source sandstone that matches in colour, texture, and geological type. Local quarries or architectural salvage yards in Scotland might have what you need.
Protective Treatments
Water Repellents: These can help keep water out, reducing risk of freeze-thaw damage and biological growth. However, they need to be breathable to allow moisture within stone to escape.
Consolidants vs. Repellents: Understand that consolidants strengthen stone, while repellents protect surface. Sometimes, both might be used, but it’s crucial to apply them correctly.
Considerations: Any treatment should respect the stone’s natural aging process. Over-treating can sometimes lead to a build-up of salts or a change in stone’s appearance.
DIY vs. Professional Help
While some minor repairs might be easy to do for a skilled homeowner, structural issues, or work on listed buildings should always involve professionals. They have tools, knowledge, and often legal permissions required.
Choosing a Professional: Look for someone with a track record in conservation, preferably with experience in Scottish sandstone. Organisations like Historic Environment Scotland can offer guidance or recommendations.
Preventive Measures
Weatherproofing
Proper Drainage: Ensure that water drains away from sandstone walls effectively. Poor drainage can lead to water pooling, which seeps into the sandstone, causing erosion and freeze-thaw damage during colder months.
Protective Treatments
Choosing the Right Sealant: While not always necessary, sealants can offer an extra layer of protection against moisture and pollutants. It’s crucial to choose a breathable sealant specifically designed for sandstone to prevent trapping moisture inside the stone, which can lead to deterioration.
Application: Sealant should be applied by a professional to ensure an even coverage and correct handling, which is especially important for historic or structurally sensitive walls.
Environmental Considerations
Vegetation Control: Keep vines and heavy plants away from sandstone walls. Roots and invasive growth can cause physical damage and moisture retention against the wall.
Pollution Management: In urban areas, pollution can accelerate the decay of sandstone. Regularly cleaning the stone can help minimize this risk, but it should be done gently, as described in routine maintenance tips.
Legal and Conservation Considerations
Listed Buildings
What Does ‘Listed’ Mean? If your property is listed, it means it’s recognised for its special architectural or historic interest. There are different categories (A, B, and C in Scotland), with A being the most significant.
Permissions Needed: Any changes, including repairs or maintenance that might affect the character of a listed building, often require Listed Building Consent. This includes repointing, replacing stones, or applying treatments. Always check with your local planning authority or Historic Environment Scotland before starting work.
Grants and Funding: There might be grants available for the conservation of listed buildings. These can help cover the costs of professional assessments or specialized restoration work.
Case Studies
The Restoration of Edinburgh's Old Town Tenement
A 19th-century tenement in Edinburgh’s historic Old Town was showing signs of severe weathering due to years of exposure to the weather.
The facade was crumbling, with significant loss of detail in ornate sandstone carvings, and biological growth was rampant due to poor drainage.
Assessment: A thorough survey by our conservation experts identified extent of damage and types of sandstone used.
Cleaning: Gentle steam cleaning was used to remove biological growth without damaging the stone.
Repairs: Where possible, stones were consolidated. For severely damaged sections, matching sandstone from a local quarry was used for replacements.
Protection: Breathable water repellent was applied, and improvements were made to the building’s drainage system.
Outcome: The tenement now stands as a testament to successful restoration, preserving its historical charm while ensuring structural integrity.
The Coastal Cottage in Fife
A charming but weather-beaten cottage near the Fife coast faced issues with salt damage and erosion.
Sea spray was causing the sandstone to degrade at an accelerated rate, with parts of the wall becoming dangerously weak.
Solution:
Stabilisation: Initial stabilisation involved applying a consolidant to strengthen the weakened stone.
Salt Removal: Regular rinsing with fresh water in spring to mitigate salt crystallisation.
Barrier: A low, decorative wall was built to deflect some of the sea spray, combined with planting salt-resistant shrubs.
Outcome: The cottage’s walls have been preserved, with added barriers significantly reducing impact of salt and sea spray, showcasing how environmental adaptations can aid in stone conservation.
The Community Project in Stirling
A community-led initiative to restore a series of sandstone boundary walls around a historic church in Stirling.
Lack of maintenance had led to overgrowth, mortar decay, and some vandalism.
Solution:
Community Involvement: Local volunteers were trained in basic stone repair techniques by heritage experts.
Repointing: Using traditional lime mortar, the community repointed walls, learning about the importance of breathability in stone work.
Education: Workshops were held to educate residents on the historical significance of sandstone in local architecture.
Outcome: Not only were the walls restored, but the project also fostered community spirit and increased local awareness about heritage preservation.
Old mill house Allanton North Lanarkshire
The Old mill house building, was facing issues with pollution-related decay.
Urban pollution had darkened the sandstone and started to eat away at the surface, alongside natural weathering.
Solution:
Cleaning: A combination of micro-abrasive techniques and chemical cleaning was used to carefully remove pollution deposits without harming the stone.
Restoration: Where carvings had lost detail, skilled stonemasons recreated them using photographs and historical records.
Ongoing Care: A maintenance plan was put in place, including regular inspections and cleaning schedules tailored to urban environments.
Outcome: The Sandstone wall was returned to its former glory, with ongoing care ensuring it remains a proud symbol of family.
The Importance of Professional Expertise in Sandstone Care
As we have discussed, care and restoration of sandstone require specific techniques and knowledge, particularly when dealing with the unique challenges posed by the Scottish climate and environmental conditions.
Why Professional Help Is Crucial
Expertise in Materials and Techniques: Our professionals in stone conservation have extensive knowledge of the types of sandstone specific to Scotland and best practices for their care. They can identify right materials for repairs and the safest cleaning methods that won’t damage the stone.
Understanding of Legal and Conservation Requirements: Our specialists are well-versed in the regulatory landscape, including necessary permissions and conservation guidelines, which is essential for any work on historic structures or those located in conservation areas.
Advanced Skills for Complex Issues: Certain conditions, such as severe erosion, structural damage, or issues arising from improper previous repairs, require the advanced skills and tools that only professionals can provide.
Long-Term Cost Efficiency: While hiring professionals may seem expensive upfront, their ability to accurately diagnose problems and implement effective solutions can save significant money in the long run by preventing costly future damages.
If you own or manage a property with sandstone walls, don’t hesitate to connect with our conservation expert to assess current condition and discuss maintenance plans.
Investing in professional care is investing in the future of our heritage— Call us now!