Cement and sand plaster method statement on Concrete surface

1. Purpose

The purpose of this method statement is to outline the systematic approach for applying cement and sand plaster on concrete surfaces, ensuring that the work is carried out safely, efficiently, and in accordance with quality standards.

2. Scope of Work

This method statement covers the procedure for applying cement and sand plaster on concrete surfaces, including walls, ceilings, and columns, for both internal and external applications.

3. Materials

Cement: Ordinary Portland Cement (OPC) or as specified, conforming to relevant standards (e.g., ASTM C150).
Sand: Clean, well-graded sand, free from silt, clay, and other impurities; conforming to ASTM C144 or equivalent.
Water: Clean and potable, free from harmful substances.
Bonding Agent: Polymer-based bonding agent to enhance adhesion on smooth concrete surfaces (as required).
Plaster Mesh: Galvanized expanded metal mesh or fiberglass mesh for reinforcement (optional but recommended for large areas or where cracks are likely).

4. Tools & Equipment

Trowels (steel and wooden floats)
Hawk
Plumb bob
Spirit level
Straight edge
Buckets for mixing
Mechanical mixer
Measuring tape
Brushes and sponges
Scaffolding or ladders (if required)
Chisel and hammer (for surface preparation, if necessary)

5. Safety Precautions

Ensure all workers wear appropriate personal protective equipment (PPE) such as safety helmets, gloves, goggles, and safety boots.
Ensure proper scaffolding and secure ladders are in place when working at heights.
Maintain adequate ventilation in enclosed spaces to avoid inhalation of dust.
Handle cement carefully to prevent skin irritation and other potential hazards.

6. Preparation

Surface Preparation:

Inspect the concrete surface to ensure it is sound, clean, and free from dust, grease, oil, and loose particles. Remove any formwork oil, curing compounds, or laitance using mechanical means such as wire brushing, sanding, or light chiseling.
Roughen smooth concrete surfaces by chiseling or using a bush hammer to create a key for the plaster to adhere. This step is crucial as smooth concrete surfaces do not provide a good mechanical bond for plaster.
Clean the surface thoroughly after roughening to remove all loose material and dust.
Wet the concrete surface uniformly before applying plaster. The surface should be damp but not saturated to prevent it from absorbing water from the plaster too quickly.

Application of Bonding Agent:

Apply a bonding agent to the concrete surface if specified, particularly for very smooth or dense surfaces. Follow the manufacturer’s instructions for mixing and application.
Allow the bonding agent to become tacky before proceeding with plaster application.

7. Mixing

Proportion:

A typical mix ratio for cement and sand plaster on concrete surfaces is 1:4 (cement: sand) by volume. This ratio may vary depending on project specifications and the location (internal or external).

Mixing:

Measure the required quantities of cement and sand.
Dry mix the cement and sand until a uniform color is achieved.
Gradually add water while mixing to achieve a workable consistency. The mix should be smooth, lump-free, and cohesive.
Avoid adding excess water, as this can weaken the plaster.

8. Application Procedure

First Coat (Scratch Coat):

Apply the first coat of plaster, usually 10 to 12 mm thick, onto the prepared surface using a trowel. Start from the bottom and work upwards.
Use a straight edge to level the plaster and ensure it is applied evenly.
While the plaster is still fresh, create a rough texture by scratching the surface with a notched trowel or comb. This provides a key for the next coat.
Allow the scratch coat to cure for at least 24 hours by keeping it moist with water.

Second Coat (Finish Coat):

After the scratch coat has cured, apply the second coat of plaster, typically 6 to 8 mm thick.
Use a straight edge and spirit level to ensure the plaster is even and flat.
Smooth the surface using a wooden float for a medium finish or a steel trowel for a fine finish, depending on the required texture.
In areas prone to cracking or in large spans, consider embedding plaster mesh within the first coat for added reinforcement.

9. Finishing

Final Smoothing:

Once the plaster has partially set, use a steel trowel to achieve a smooth finish. Avoid over-troweling, which can cause the surface to become too smooth and reduce its bonding capability for subsequent layers (e.g., paint or wallpaper).
For a textured finish, use a sponge float or brush to create the desired pattern while the plaster is still workable.

Curing:

Curing is critical to prevent cracks and ensure the plaster develops its full strength. Begin curing 24 hours after application by gently spraying water on the plastered surface.
Continue curing by keeping the plaster damp for 7 days, ensuring that it does not dry out too quickly, especially in hot or windy conditions.

10. Quality Control

Thickness Check: Verify that the plaster thickness meets project specifications using a straight edge and spirit level.
Surface Evenness: Ensure the plastered surface is even, level, and free from undulations or waves.
Adhesion: Tap the plastered surface lightly to check for any hollow spots, indicating poor adhesion.
Finish Quality: Inspect the surface finish to ensure it is smooth, consistent, and free from cracks, voids, or other defects.

11. Clean-Up

Clean tools and equipment immediately after use to prevent cement from hardening on them.
Remove excess plaster from adjacent surfaces while it is still wet.
Clean the work area, ensuring no plaster residues or debris are left behind.

12. Completion & Handover

Perform a final inspection to ensure the plastering work is in compliance with project specifications and quality standards.
Document the completed work, noting any deviations or issues addressed during the plastering process.
Hand over the plastered surfaces, making them ready for subsequent treatments such as painting or finishing.

Conclusion

This method statement outlines a detailed procedure for applying cement and sand plaster on concrete surfaces, ensuring a high-quality finish that adheres properly and remains durable. By following these steps, including proper surface preparation, mix proportions, application, and curing, the plastering work will meet the required standards and provide a smooth, aesthetically pleasing surface that is both functional and long-lasting.