Plastering is an essential element in construction. It serves multiple purposes, from providing a smooth surface to protecting structures from external elements.
Whether working on interior or exterior walls, plastering is important in achieving durability and aesthetic appeal. Here’s a detailed look at the plastering process, tools required, and steps involved in delivering a professional-quality finish.
Let’s get straight to the point
Plastering applies a thin mortar layer to interior and exterior walls to smooth surfaces, protect against moisture, and enhance durability. Key steps include:
- Preparing the wall.
- Applying a PVA solution for adhesion.
- Mixing plaster.
- Apply multiple coats while smoothing and polishing the surface.
Internal plastering provides insulation and fire resistance, while external plastering protects against weather. Tools like trowels, floats, and scaffolding are essential.
Bullmarks ensure uniform plaster thickness. After curing, walls can be painted or wallpapered for a finished look.
Preparing For Plastering
Proper preparation is essential for successful plastering. Follow these steps to ensure your surfaces are ready:
- Protect the Floor: Use dust sheets to protect your floors and collect any falling plaster.
- Clean the Surface: Ensure the walls are free from dust, debris, oil, or grease. For older or damaged walls, use a wire brush for deep cleaning.
- Repair the Wall: Patch holes or cracks with screen tape or a concrete mix. For new plasterboards, apply screen tape to cover the joints before plastering.
Step-By-Step Plastering Process
1. Applying PVA Solution
Before applying plaster, coat the walls with a mixture of PVA (Polyvinyl Acetate) glue and water (typically 4:1). This seals the surface, ensuring the plaster adheres properly and dries evenly.
Brush the PVA mixture onto the walls and let it dry.
2. Mixing The Plaster
Mix the plaster according to the manufacturer’s instructions. Wear a dust mask during this step to avoid inhaling fine particles.
Pour cold water into a bucket, then gradually add plaster. Stir until the mixture reaches a smooth, thick consistency like custard.
3. Applying The First Coat Of Plaster
Once your plaster is ready, apply the first coat using a hawk board, trowel, and floating tool. Start at the bottom left corner of the wall and work your way up.
Use light pressure to spread the plaster evenly. Lay the float flat as you work across each section to ensure smooth surfaces.
4. Skimming And Polishing
Allow the plaster to dry for about 20 minutes. Once it’s slightly firm, use your trowel to smooth the surface.
Pay close attention to edges and corners, often trickier to perfect. A corner trowel can help you achieve clean lines in these areas.
5. Scraping The Surface
While not essential, scraping the surface between coats can help the second layer of plaster adhere better. A devilling float or kitchen fork can be used for this purpose.
Alternatively, apply the second coat while the first is still slightly damp to promote adhesion.
6. Applying The Second Coat Of Plaster
Mix a new batch of plaster and apply a second coat. This coat should be thinner than the first—no more than 2 mm thick. Smooth it over the wall similarly, ensuring an even surface.
7. Finishing The Plaster
Once the second coat has dried slightly, begin polishing the surface. Spray the wall lightly with water and use the trowel to smooth out any imperfections, moving inwardly.
A clean float will help you achieve a seamless finish. After the plaster has dried completely, sandpaper can be used to remove any minor rough patches.
Final Touches: Painting And Wallpapering
After the plaster is fully cured, the wall is ready for paint or wallpaper. If you plan to wallpaper the surface, apply an undercoat of paint or adhesive for better results.
This ensures the wall is well-sealed, preventing moisture from affecting the new plaster.
Tools And Materials Needed
- Trowel and bucket trowel
- Plasterer’s float
- Hawk Board
- Corner trowel
- Mixing stick or paddle
- Buckets (at least two)
- PVA glue
- Dust sheets
- Fine plaster
- Clean water
- Stepladder or stilts
- Sandpaper
- Dust mask
Internal Plastering: Steps And Techniques
Internal plastering focuses on giving interior walls a smooth, solid finish. It also provides some insulation and acts as a fire barrier. Here’s how to prepare and plaster internal walls:
1. Preparing The Wall
Mortar joints should remain unfilled to give the plaster something to grip. Scrape off excess mortar and point the joints.
Clean the wall with a wire brush to remove any contaminants. If holes or cracks exist, fill them with concrete and allow them to cure.
2. Plastering The Wall
For internal plastering, the mortar is typically a mix of cement and sand (ratio of 1:3). Apply the first layer of plaster to the surface, ensuring the joints are covered and the surface is levelled.
The plaster thickness usually ranges between 12 mm and 15 mm.
3. Curing The Plaster
Once the plaster is levelled, allow it to set. Internal plaster typically requires a seven-day curing period to ensure durability.
External Plastering: Protecting Against Weather
External plastering is designed to protect a building’s outer walls. This layer is a waterproof barrier, shielding the structure from environmental damage.
External plaster is usually rougher and thicker than its internal counterpart.
1. Preparing For External Plastering
External plastering should only begin after all blockwork and masonry is complete. Scaffolding is required to reach higher walls, and all joints between masonry and concrete surfaces must be thoroughly cleaned.
2. Applying The Plaster
Start from the top of the building and work your way down. Use a cement-sand mix (typically 1:4 ratio) and apply the plaster in layers, with each layer no thicker than 20 mm. Chicken mesh should be used on joints to prevent cracks from developing.
3. Ensuring Durability
External plaster should be cured for at least seven days to ensure it adheres properly and provides long-term protection. After curing, apply a primer to prevent weathering and to prepare the surface for painting or other finishes.
Using Bullmarks For Uniform Thickness
Plasterers use bull marks to ensure an even plaster thickness across a surface. These are 10 cm by 10 cm patches of plaster applied at regular intervals along the wall.
The bull mark guides plaster thickness, helping the plasterer maintain consistency across the entire surface.
Scaffolding For External Plastering
Scaffolding is essential for reaching higher walls when plastering externally. There are two main types of scaffolding used:
- Single Scaffolding: Vertical wooden or bamboo segments planted into the ground at 1.2 to 2.5 metres intervals.
- Double Scaffolding: This setup uses two rows of standards and is more stable and durable. It’s preferred for projects requiring heavy-duty support.
Conclusion
Plastering is a vital construction process that enhances a building’s durability and aesthetics. Whether you are plastering interior or exterior walls, following the proper techniques—such as using PVA, mixing plaster correctly, and ensuring uniform application—will result in a smooth and long-lasting finish.
By preparing thoroughly, using the right tools, and following best practices, you can achieve professional-level results in any plastering project.
