Plastering is a common practice used to create smooth and even surfaces on walls and ceilings. However, when it comes to renovating or repairing older buildings, the question arises whether it is possible to plaster over old lime plaster. In this article, we will explore the suitability of plastering over old lime plaster, the considerations to keep in mind, and the steps involved in the process.
Understanding Lime Plaster
Lime plaster is a traditional building material that has been used for centuries. It is composed of lime, sand, and water, which creates a durable and breathable surface. Lime plaster has many advantageous properties, such as its ability to absorb moisture and prevent the buildup of mold and mildew. It also allows moisture to evaporate, which is vital for older buildings that lack a damp-proof membrane.
Considerations Before Plastering Over Old Lime Plaster
Before proceeding with plastering over old lime plaster, several factors should be taken into account:
- Condition of the Existing Lime Plaster: Inspect the condition of the old lime plaster. If it is loose, crumbling, or showing signs of significant deterioration, it is not suitable for plastering over. In this case, it is recommended to remove the old plaster and reapply a fresh lime plaster finish.
- Compatibility of Materials: Ensure that the plaster you intend to use is compatible with lime plaster. Traditional lime-based plasters or modern lime-containing plasters are typically the best choices. Using a gypsum-based plaster over lime plaster is not advisable due to potential incompatible reactions between the two materials.
- Adhesion and Priming: Adequate adhesion is essential for the new plaster to bond with the old lime plaster. Before plastering, the surface should be properly cleaned, and a primer or bonding agent specifically designed for use with lime plaster should be applied.
Process of Plastering Over Old Lime Plaster
If you have assessed that plastering over the old lime plaster is possible, follow the steps outlined below:
- Preparation: Protect the surrounding areas with drop cloths or plastic sheeting. Use a wire brush to remove loose particles and clean the surface thoroughly. Repair any cracks or damage in the old plaster.
- Priming: Apply a suitable primer or bonding agent to the old lime plaster. This will enhance adhesion and ensure a strong bond between the old and new layers of plaster.
- Mixing Plaster: Follow the instructions provided with your chosen plaster to create a consistent mixture. Whether you opt for traditional lime-based plaster or a lime-containing alternative, ensure you achieve the correct ratio of water to plaster.
- Applying the New Plaster: Start applying the plaster using a trowel in even, thin layers. Smooth out the surface and ensure a consistent thickness throughout. It may be necessary to build up multiple coats, allowing each layer to dry before applying the next.
- Finishing and Curing: Once the plaster has been applied and is still slightly damp, use a plaster float or sponge to achieve the desired smoothness and texture. Allow the plaster to dry and cure completely before applying any paint or finishes.
Plastering over old lime plaster can be a viable option for renovating older buildings without compromising their breathable properties. By considering the condition of the existing lime plaster, compatibility of materials, and following the appropriate steps, you can achieve a successful plastering job. Remember, proper preparation, priming, and application techniques are crucial for a durable and aesthetically pleasing finish.