Proper wall preparation is critical to ensuring a smooth, long-lasting plaster finish. If the wall is not adequately prepared, the plaster may not adhere well, leading to cracks or peeling over time.
This guide outlines the necessary steps to prepare a wall for plaster application, cleaning, repair, priming, and moisture control.
Let’s get straight to the point.
Proper wall preparation is key to achieving a smooth and durable plaster finish. Clean the surface, remove loose paint or wallpaper, and repair any cracks or damage.
Control the wall’s suction by wetting or using a bonding agent if necessary. Prime the wall to ensure better plaster adhesion and an even and level surface.
Protect surrounding areas before applying high-quality plaster, and allow it to cure fully. Careful preparation enhances durability, improves adhesion, and prevents future structural issues.
Steps In Preparing The Wall For Plaster Application
1. Clean The Wall Surface
Start by cleaning the wall’s surface. The goal is to remove all dirt, dust, and debris, ensuring that the plaster has a solid surface to adhere to.
- Tools Required: Use a vacuum cleaner or a firm brush to remove dust and dirt.
- Wallpaper and Paint Removal: Use a putty knife to scrape away loose or flaking paint and wallpaper. If necessary, use a paint stripper for stubborn areas.
Make sure the wall is dry before moving on to the next step.
2. Inspect The Wall For Damage
Once the wall is clean, inspect it for any damage, including cracks, holes, or signs of efflorescence (white stains). Early detection of these problems will save you time and effort.
- Cracks: Check for both small hairline cracks and larger structural cracks.
- Flaking Paint or Plaster: Identify areas where the paint or plaster is peeling off.
- Efflorescence: Look for powdery white deposits on the surface caused by water entering the wall and bringing salts to the surface.
- Mould or Algae: Any signs of mould or algae should be removed immediately to prevent future issues.
3. Repair Any Wall Damage
Before applying plaster, repair any damage to the wall. Addressing these issues is essential for ensuring the plaster adheres well and lasts long.
Filling Small Cracks And Holes
Use a filler made specifically for external walls for small cracks and holes. Apply the filler carefully and allow it to dry according to the manufacturer’s instructions.
- Sanding: Once the filler is dry, smooth the surface with medium-grit sandpaper.
Repairing Larger Cracks
For larger cracks, you will need masonry repair mortar.
- Preparation: Clean the crack with a wire brush and dampen the area before applying the mortar.
- Application: Use a trowel to apply the mortar, ensuring the crack is filled. Once applied, smooth the surface with the trowel.
After completing the repairs, consider applying a waterproof sealer to protect the repaired areas from future moisture damage.
4. Control Wall Suction
Controlling the wall’s suction is an important step that affects how quickly the plaster dries and how well it adheres to the surface.
Understanding Wall Suction
Different wall materials have varying suction levels or how quickly they absorb moisture. For example, bricks have high suction, while plasterboard has low suction.
- High-suction walls absorb moisture quickly, which can cause the plaster to dry too fast. This makes it harder to achieve a smooth finish.
- Low-suction walls absorb moisture slowly, giving you more time to work with the plaster before dries.
Managing Suction
To control suction, you may need to wet the wall slightly before plastering or use a bonding agent for very smooth surfaces.
- Wetting the Surface: Lightly moisten the wall with water to prevent the plaster from drying too quickly.
- Bonding Agents: Apply a bonding agent to low-suction surfaces like smooth concrete to improve adhesion.
5. Prime The Surface
Priming the wall helps create a consistent surface for the plaster to adhere to. The type of primer you use will depend on the wall’s material and the type of plaster you plan to apply.
- Choosing the Right Primer: Use a primer compatible with the plaster and the wall material. Check the manufacturer’s instructions to ensure you’re using the correct product.
- Application: Apply the primer evenly across the surface and allow it to dry fully before proceeding.
6. Ensure The Surface Is Even And Plumb
Before applying plaster, ensure the wall is level and plumb (perfectly vertical).
- Use a Level: Check that the surface is level and even. Use additional filler or sanding to smooth out any bumps or uneven areas if necessary.
- Plumb Line: For vertical alignment, use a plumb line to verify that the surface is straight. This will help ensure a smooth final result.
7. Protect Surrounding Areas
Before plastering, take steps to protect areas that should not come into contact with the plaster.
- Cover Furniture and Floors: Lay down drop cloths or plastic sheets to protect the floor and any nearby furniture.
- Painter’s Tape: Use painter’s tape to cover light switches, electrical outlets, and other fixtures. This will keep them free of plaster splatters.
8. Apply The Plaster
Once the wall is clean, repaired, primed, and prepped, it’s time to apply the plaster. Ensure you choose a high-quality plaster for external use, such as silicone or acrylic render.
Mixing The Plaster
Follow the manufacturer’s instructions when mixing the plaster.
- Mixing Instructions: Combine the plaster with water per the guidelines, ensuring a consistent texture.
Applying The Plaster
- Tools: Use a stainless steel trowel to apply the plaster to the wall.
- Technique: Spread the plaster evenly across the surface, avoiding bumps or uneven patches.
- Levelling: Use a straight edge to ensure the plaster is level. Once the first coat has dried, apply a second coat if necessary.
Drying Time
Depending on weather conditions, plaster drying times can vary, so check the product specifications and monitor the plaster as it dries.
9. Suction Control During Application
As you apply the plaster, continue to monitor the suction level of the wall.
- High Suction Walls: On high suction walls like brick, you may need to mist the wall with water throughout the application to slow the drying process.
- Low-Suction Walls: Low-suction walls, such as plasterboard, may not require as much concern about moisture absorption.
10. Final Touches
After the plaster has dried, finish the surface as needed.
- Smoothing: Using a float or sponge to smooth the plaster ensures an even finish.
- Curing Time: Follow the manufacturer’s instructions and allow the plaster to cure fully before painting or adding other finishes.
Conclusion
Preparing a wall for plaster application involves several essential steps: cleaning, repairing, controlling suction, and priming.
Proper preparation ensures better adhesion, a smoother finish, and a longer-lasting result.
Following these steps, you can create a strong, well-prepared surface supporting a high-quality plaster application.
Whether working with high-suction bricks or low-suction plasterboard, careful planning and execution will lead to a more professional, durable result.
Preparing the wall also enhances energy efficiency and prevents structural damage, making the effort worthwhile in the long run.
FAQs About Plastering
How Do I Address Moisture Issues Before Plastering?
Identify the source of moisture infiltration, such as leaking pipes or roof leaks, and repair them promptly. Allow the wall to dry completely before plastering, and consider applying a moisture barrier or waterproofing membrane if necessary.
What Should I Do If The Wall Surface Is Uneven Or Rough?
Use a plasterer’s float or sanding block to smooth out rough areas and level uneven surfaces. Fill in low spots or depressions with a levelling compound or additional layers of plaster as needed.
Should I Apply A Scratch Coat Or Base Coat Before The Final Plaster Layer?
Yes, applying a scratch or base coat provides a rough surface for the final plaster layer to adhere to and helps minimise cracking and shrinkage. Follow manufacturer guidelines for mixing and applying the base coat.
How Do I Protect Adjacent Surfaces And Fixtures During Wall Preparation?
Cover floors, furniture, and fixtures with drop cloths or plastic sheeting to protect them from dust, debris, and splatters during wall preparation and plaster application.
What Safety Precautions Should I Take During Wall Preparation?
Wear appropriate safety gear such as gloves, goggles, and a dust mask to protect against dust, debris, and chemical exposure. Use ladders or scaffolding safely to reach high areas, and follow manufacturer instructions for handling and storing chemicals and tools.
