To render a wall with sand and cement, you'll typically mix sand, cement, and often lime, then apply this mixture in layers to create a smooth or textured finish.
Rendering a wall is a practical way to weatherproof, protect, and improve its appearance. The exact process involves preparing the surface, mixing the render, and applying it correctly in stages.
Essential Render Mix
Based on common practice and specific guidance, an effective render mix for walls includes lime to enhance workability and reduce cracking.
Recommended Mix Ratio:
| Component | Parts | Purpose Note |
|---|---|---|
| Lime | 1 | Improves flexibility & breathability |
| Cement | 1 | Provides strength & hardness |
| Sand | 6 | The main aggregate |
Using 1 part lime to 1 part cement and 6 parts sand is a standard mix for rendering.
Choosing the Right Sand
The type of sand significantly impacts the render's performance and finish.
- Base Layer (Scratch Coat): Use coarse sand. This provides better grip for the next layer and helps prevent shrinkage cracks.
- Top Layer (Finish Coat): Use finer sand. This allows for a smoother finish or more detailed textures.
Using coarse sand for the base layer and finer sand for the top layer will ensure your render lasts for years to come.
Step-by-Step Rendering Process
Rendering involves multiple stages to ensure a durable and high-quality finish.
1. Prepare the Wall Surface
Proper preparation is key to a successful render.
- Clean the wall thoroughly, removing any loose material, paint, algae, or dirt.
- Repair any cracks or holes in the existing wall.
- Dampen the wall slightly before applying the render; this helps prevent the wall from drawing water out of the mix too quickly, which can lead to cracking.
2. Mix the Render
Mixing the render correctly ensures consistency and strength.
- Measure your materials accurately according to the recommended ratio (1 part lime, 1 part cement, 6 parts sand).
- Combine the dry ingredients (lime, cement, sand) thoroughly.
- Gradually add clean water while mixing, until you achieve a workable consistency – not too wet or too dry. It should be stiff enough to stay on a trowel but wet enough to spread easily.
3. Apply the Scratch Coat (Base Layer)
This is the first layer applied to the prepared wall.
- Using a hawk and trowel, apply the mixed render firmly onto the wall surface. Work upwards, pressing the mix onto the wall to ensure good adhesion.
- Aim for a thickness of around 10-15mm.
- Once a section is applied, use a straight edge or 'darby' to level the surface, removing excess material.
- Immediately scratch the surface horizontally with a scratching tool or comb. This creates a 'key' for the top coat to bond to.
- Allow this layer to cure properly, typically for at least 24-48 hours, keeping it damp if necessary, especially in warm weather.
Apply your mixture to your walls following the method used in our 'how to render a garden wall' section. (Note: While the specific 'garden wall' guide isn't provided here, the method generally involves applying in layers and finishing, as described in these steps.)
4. Apply the Top Coat (Finish Layer)
This layer provides the final appearance and protection.
- Ensure the scratch coat is clean and slightly damp.
- Mix a fresh batch of render, using finer sand as recommended.
- Apply the top coat over the scratch coat, typically 5-10mm thick.
- Level the surface using a float or straight edge.
- Finish the surface according to the desired texture – this could involve rubbing with a wooden or plastic float for a smooth finish, or using a sponge or other tools for textured effects.
5. Curing
Proper curing is essential for the render's strength and durability.
- Keep the finished render damp for several days by lightly misting it with water. This allows the cement and lime to hydrate correctly.
- Protect the render from direct sunlight, wind, or frost while it cures.
Following these steps, using the specified mix ratio and sand types, will help you achieve a durable and long-lasting rendered wall.
