Method Statement for Dry-Mix Cement and Sand Plastering on External Walls

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

1. 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.

1. 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

1. 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.

1. 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

1. 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.

1. 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.

1. 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

1. 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.

1. 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.