1. Purpose
The purpose of this method statement is to outline the procedure for applying dry-mix cement and sand plaster on external walls, ensuring the work is executed safely, efficiently, and to a high-quality standard that meets the project specifications.
2. Scope of Work
This method statement covers the preparation, mixing, application, and curing processes for dry-mix cement and sand plaster on external masonry or concrete walls.
3. Materials
- Dry-Mix Cement and Sand Plaster: Pre-blended mixture of cement, sand, and additives, specifically designed for external applications and conforming to relevant standards.
- Water: Clean and potable, free from impurities and contaminants.
- Bonding Agent: For enhanced adhesion on smooth or dense surfaces (as required).
- Plaster Mesh: Galvanized or fiberglass mesh for reinforcement at joints, corners, and over large spans prone to cracking (optional but recommended for external walls).
4. Tools & Equipment
- Trowels (steel and wooden floats)
- Hawk
- Spirit level
- Plumb bob
- Straight edge
- Buckets for mixing (if manual mixing is required)
- Mechanical mixer or drill with mixing paddle
- Measuring tape
- Brushes and sponges
- Scaffolding or ladders (for working at heights)
- Spray equipment (if using mechanical application)
- Tarpaulin or protective sheeting (to cover walls during adverse weather conditions)
5. Safety Precautions
- Ensure that all workers wear appropriate personal protective equipment (PPE), including safety helmets, gloves, goggles, and safety boots.
- Secure scaffolding and ladders to prevent falls when working at heights.
- Implement measures to prevent dust inhalation, especially when mixing dry materials.
- Be mindful of weather conditions, especially wind, rain, or extreme heat, which can affect the application and curing of plaster.
6. Preparation
- Surface Preparation:
- Inspect the external wall surface to ensure it is clean, dry, and free from dust, dirt, oil, grease, and loose particles.
- Roughen smooth surfaces with a wire brush, chisel, or mechanical means to provide a key for the plaster. On smooth concrete surfaces, apply a bonding agent if necessary.
- Repair any cracks or voids with suitable repair mortar before applying the plaster.
- Protect adjacent surfaces (windows, doors, etc.) with tarpaulin or sheeting to prevent them from being stained or damaged during plastering.
- Dampen the wall surface with clean water before plastering. The wall should be uniformly moist to prevent the rapid absorption of water from the plaster.
- Setting Out Levels:
- Mark reference points, levels, and guide screeds on the wall using a spirit level, plumb bob, and chalk line to ensure even application and desired thickness of plaster.
7. Mixing
- Dry-Mix Preparation:
- Follow the manufacturer’s instructions for mixing the dry-mix plaster. Usually, this involves adding the dry-mix material to a clean mixing container.
- Gradually add water to the dry mix while continuously stirring until a uniform, lump-free mixture is achieved.
- Use a mechanical mixer or a drill with a mixing paddle to ensure the mixture is consistent and smooth.
- Consistency:
- Ensure the plaster has a workable consistency that can be easily applied to vertical surfaces. Avoid adding excess water, as it can weaken the plaster and cause sagging.
8. Application Procedure
- First Coat (Scratch Coat):
- Apply the first coat of plaster to the external wall, usually about 10 to 12 mm thick. Use a trowel and apply in a uniform layer from the bottom upwards.
- Use a straight edge to level the plaster and remove excess material, ensuring an even thickness.
- While the plaster is still wet, scratch the surface with a notched trowel or comb to create a rough texture, which will serve as a key for the subsequent coat.
- Allow the scratch coat to cure for at least 24 hours, keeping it moist by spraying water if necessary.
- Second Coat (Finish Coat):
- After the scratch coat has adequately cured, apply the second coat of plaster, typically 6 to 8 mm thick.
- Use a straight edge and spirit level to ensure the surface is smooth, even, and aligned with the reference points.
- Smooth the surface with a wooden float for a medium finish or a steel trowel for a finer finish, depending on the required texture.
- Consider embedding plaster mesh within the first coat, particularly around corners, joints, and large spans, to reinforce the plaster and prevent cracking.
- Machine Application (If Applicable):
- If using mechanical spray equipment, ensure that the machine settings are adjusted according to the manufacturer’s guidelines to achieve the desired thickness and finish.
- Spray the plaster evenly across the wall and immediately follow with a straight edge to level the material.
9. Finishing
- Final Smoothing:
- After the plaster is applied and has partially set, use a steel trowel to achieve a smooth finish. For textured finishes, use a sponge float or brush while the plaster is still workable.
- Pay extra attention to the corners, edges, and junctions to ensure a neat and consistent finish.
- Curing:
- Begin curing after 24 hours by lightly spraying water on the plastered surface. Ensure proper curing for 7 days by keeping the plaster moist to prevent cracking due to rapid drying, especially under hot or windy conditions.
- Protect the plastered surface from rain, direct sunlight, and strong winds during the curing period by using tarpaulin or other suitable protective covers.
10. Quality Control
- Thickness Verification: Use a straight edge and spirit level to verify that the plaster thickness meets the project specifications.
- Surface Evenness: Ensure that the plastered wall is flat, even, and free from undulations or waves.
- Adhesion Testing: Tap the surface lightly to check for hollow spots, which may indicate poor adhesion or insufficient compaction.
- Finish Inspection: Inspect the surface for any cracks, voids, or other defects and ensure that the texture and finish are consistent.
11. Clean-Up
- Clean all tools and equipment immediately after use to prevent the plaster from hardening on them.
- Remove excess plaster from adjacent surfaces and clean any spillage while it is still wet.
- Ensure the work area is clean, with all debris and waste materials properly disposed of.
12. Completion & Handover
- Conduct a final inspection of the plastered wall to ensure it complies with the project specifications and quality standards.
- Document the completion of the plastering work, including any deviations or corrective actions taken during the process.
- Hand over the plastered surfaces to the client or project manager, ensuring they are ready for any subsequent treatments, such as painting or waterproofing.
Conclusion
This method statement provides a comprehensive guide for applying dry-mix cement and sand plaster on external walls. By following these procedures, including proper surface preparation, mixing, application, and curing, the plastering work will result in a durable, weather-resistant finish that meets the project requirements and enhances the appearance and longevity of the external walls.
