Making lime mortar with lime putty involves mixing the putty with sand in the correct proportions to achieve the desired consistency and strength. Typically, you'll need just lime putty and sand.
Here's a step-by-step guide:
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Gather Your Materials: You will need lime putty, appropriate sand (see details below), a mixing container (wheelbarrow or mortar tub), a shovel or mixing tool, and water (optional, but likely needed).
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Choose the Right Sand: The type of sand is crucial. Use sharp, well-graded sand that is free of clay, silt, and organic matter. The particle size distribution should be appropriate for the application; coarser sands are often preferred for bedding mortar.
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Determine the Mix Ratio: A common starting point is 1 part lime putty to 2-3 parts sand, measured by volume (e.g., using a bucket). The specific ratio depends on the application and the quality of the lime putty and sand. Softer, weaker stones may require a ratio of 1:3, while stronger stones can use 1:2.
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Mix the Ingredients:
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Dry Mixing (Recommended): Place the sand and lime putty in the mixing container. Mix thoroughly before adding any water. This helps ensure the lime putty is evenly distributed throughout the sand. The mixture should become smooth and 'fatty' as the lime coats the sand particles. This is best done with a mechanical mixer.
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Water Addition (If Needed): Slowly add water, a little at a time, until the mortar reaches a workable consistency. The ideal consistency is similar to that of bricklaying mortar – plastic and easily spreadable, but not too wet.
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Check the Consistency: The mortar should be cohesive and stick to your trowel without being too sticky. It should also retain its shape when placed.
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Use Immediately: Lime mortar is best used soon after mixing. It can be stored for a short period in an airtight container, but it will begin to stiffen over time. Avoid using mortar that has begun to dry out.
Important Considerations:
- Sands: The sand's quality significantly impacts the mortar's strength and workability. Angular sands are generally preferred. Consider using a mix of coarse and fine sands to improve packing and reduce shrinkage.
- Lime Putty Quality: Use well-matured lime putty that is free of lumps and impurities. The longer the lime putty has matured, the better the mortar will be.
- Mixing Equipment: A mechanical mixer is highly recommended for larger batches. Hand mixing is possible but requires more effort and care to ensure thorough mixing.
- Trial Batch: It is always a good idea to mix a small trial batch to check the consistency and workability before mixing a larger quantity.
- Safety: Lime is caustic. Wear gloves and eye protection when handling lime putty and mortar.
- Curing: Lime mortar cures slowly through carbonation, absorbing carbon dioxide from the air. Protect the mortar from rapid drying by keeping it damp for the first few days after application.
