Using hydraulic lime for mortar or plaster requires careful mixing and application to achieve the best results. Here's a step-by-step guide:
Mixing Hydraulic Lime Mortar
The proper mixing technique is crucial for a durable and effective hydraulic lime mortar. Follow these steps:
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Prepare Your Mixer: Start with a clean, empty mixer. This prevents contamination and ensures accurate proportions.
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Add Initial Sand: Add one part sand to the mixer. The type of sand can vary depending on the application, but sharp sand is often preferred for mortar.
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Incorporate Lime: Add one part hydraulic lime to the mixer. Ensure the lime is evenly distributed over the sand.
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Add Remaining Sand: Add an additional 1.5 parts of sand to the mixture. This staged approach helps to ensure even blending.
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Dry Mix Thoroughly: Mix the dry ingredients for at least 5 minutes. This ensures the lime and sand are properly combined before adding water. Adequate dry mixing leads to a more consistent and workable mortar.
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Slowly Add Water: Gradually add water to the dry mix while the mixer is running. The key is to add water slowly to avoid over-wetting the mix. The desired consistency is a plastic, workable mortar that holds its shape.
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Monitor Consistency: Pay close attention to the consistency. It's much easier to add water than to remove it. Aim for a consistency that allows the mortar to be easily worked and applied without being too runny.
Important Considerations:
- Water Quality: Use clean, potable water for mixing.
- Mixing Time: Don't over-mix. Once the desired consistency is achieved, stop mixing.
- Weather Conditions: Avoid mixing in extreme temperatures (very hot or freezing conditions).
- Lime Type: Choose the appropriate type of hydraulic lime (NHL 2, NHL 3.5, or NHL 5) based on the specific requirements of your project. NHL 2 is weaker and best for more fragile substrates, while NHL 5 is stronger and better suited for more demanding applications.
- Curing: Hydraulic lime mortars require a curing period. Protect the mortar from direct sunlight, wind, and rain during the initial curing phase (typically several days). Dampen the mortar regularly with a fine mist of water to prevent it from drying out too quickly, which can lead to cracking.
Example Ratios:
| Component | Ratio | Example (Buckets) |
|---|---|---|
| Sand (First Addition) | 1 | 1 |
| Hydraulic Lime | 1 | 1 |
| Sand (Second Addition) | 1.5 | 1.5 |
| Water | As needed | - |
Application Tips:
- Surface Preparation: Ensure the surface you are applying the mortar to is clean, sound, and free of loose materials.
- Dampen the Surface: Lightly dampen the surface before applying the mortar. This helps the mortar bond properly.
- Apply in Thin Layers: Apply the mortar in thin layers, allowing each layer to set slightly before applying the next.
- Proper Tooling: Use appropriate tools for the task, such as trowels, hawks, and floats.
By following these guidelines, you can successfully use hydraulic lime for a variety of building and restoration projects.
