To make lime plaster with hydrated lime, you'll primarily mix it with aggregate (sand), aiming for a richer lime ratio than standard lime mortar.
Understanding the Basics of Lime Plaster
Lime plaster, when properly mixed and applied, provides a breathable and durable finish. It's known for its flexibility and longevity, making it a popular choice for historical restorations and environmentally conscious builds.
Key Differences: Plaster vs. Mortar
Lime plaster differs from lime mortar primarily in its lime-to-aggregate ratio. While mortar typically uses a 1:3 or 1:4 ratio, plaster needs more lime for better workability and a smoother finish.
Step-by-Step Guide to Mixing Lime Plaster
Here's a detailed breakdown of how to make lime plaster using hydrated lime:
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Gather Your Materials:
- Hydrated lime (also known as lime putty if slaked in advance)
- Fine aggregate (such as fine graded sand)
- Clean water
- Mixing container (tub or wheelbarrow)
- Mixing tools (shovel or hoe)
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Determine the Correct Ratio:
- For lime plaster, use a 1:2.5 ratio of lime to aggregate. This means for every one part of lime, you use two and a half parts of fine aggregate.
- This higher ratio of lime ensures a better finish that is suitable for plaster application.
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Mixing Process:
- Dry Mix First: Begin by placing the dry aggregate in the mixing container. Add the hydrated lime on top of the aggregate. Thoroughly mix the dry components using your shovel or hoe until they are evenly distributed.
- Add Water Gradually: Slowly introduce clean water while continuing to mix. Add small amounts of water until you achieve a workable consistency. The mix should be like thick cake batter—it should hold its shape but be easy to spread.
- Mix Thoroughly: Mix the components for a sufficient time, ensuring that there are no lumps. The mix should be homogeneous.
- Allow to Rest (optional): Some plasterers like to leave the mix to rest for about half an hour to allow the lime to hydrate further. If doing this, remix before application.
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Choosing the Aggregate
- The aggregate used can be tailored to your finish. Using fine graded sands will allow for a smoother finish.
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Application:
- Lime plaster is typically applied in two to three coats, especially when it's for interior projects. Be sure to allow each layer to cure before applying the subsequent layer.
Table: Lime Plaster Mix Ratio
| Component | Ratio |
|---|---|
| Hydrated Lime | 1 |
| Fine Aggregate | 2.5 |
Tips for Success
- Safety: Always wear appropriate safety gear, including eye protection and gloves when handling lime.
- Water Quality: Use clean water, as impurities can affect the final finish.
- Consistency is Key: Aim for a consistent mix throughout the batch.
- Practice: Before tackling a large project, it's a good idea to try mixing a small batch to get a feel for the correct consistency and ratios.
By following these steps, you will be able to make a lime plaster that is ready to be used in your chosen project. Remember to adjust the ratios slightly based on your specific requirements and the type of aggregate used. The higher ratio of lime is specifically used in plaster mixes to allow for better workability and a smooth finish.
