For pointing stone walls, the best mix is always a lime-based mortar using coarse sand.
Pointing is a crucial aspect of maintaining stone walls, protecting them from weather and ensuring their longevity. Choosing the correct mortar mix is paramount.
Why Choose a Lime-Based Mortar?
According to best practice for stone walls, the mortar mix should always be lime based. Unlike modern cement mortars, lime-based mortars are flexible and breathable, allowing the wall to expand, contract, and manage moisture effectively. This is vital for the health and stability of traditional stone structures.
Selecting the Right Sand
The type of sand used is as important as the binder. For lime mortar used in stone walls:
- Use Coarse Sand: Sands such as those sold as "sharp" or "washed" are appropriate. The varied particle sizes in coarse sand create a stronger, more permeable mortar and provide a texture that is sympathetic to natural stone.
- Avoid Fine Sand: Modern cement mortar often uses only fine-grained sand (commonly sold as "soft" or "builders' sand"). This type of sand is not appropriate for lime mortar used in stone walls. Fine sand can make the mortar dense and impermeable, trapping moisture and potentially damaging the stone or historic fabric.
Key Components for Stone Wall Pointing
Based on recommended practice, the essential ingredients are:
- Binder: Lime (Hydraulic Lime or Non-hydraulic Lime, depending on exposure and stone type - though the reference specifically mandates 'lime based' and doesn't differentiate further)
- Aggregate: Coarse Sand ("Sharp" or "Washed")
It is critical to remember that modern cement and fine "builders'" sand should be avoided for stone wall pointing.
Practical Considerations
While the reference doesn't provide specific mix ratios (these can vary based on lime type, sand, stone type, and exposure), it clearly defines the necessary materials:
- Ensure the sand is clean and free from impurities like clay or silt.
- The ratio of lime to sand will affect strength and porosity; consulting further resources or experts is recommended for specific ratios suited to your project, but the core requirement remains: lime and coarse sand.
- Only for the very finest jointed brickwork and stonework might a slightly less coarse sand be considered, but for general stone wall pointing, coarse sand is the standard.
Choosing the correct lime-based mortar with appropriate coarse sand ensures your stone walls are pointed effectively, promoting durability and preserving the structure's integrity for years to come.
