The recommended ratio of cement to sand for concrete topping, according to the provided reference, is 1 part cement to 1 1/2 parts sand.
Detailed Explanation
When preparing a concrete topping mix, the proportion of cement and sand is crucial for achieving the desired strength, workability, and durability. Traditional mixes often use a 1:3 ratio of cement to sand, but for concrete topping a modified mix is more suitable.
Recommended Mix Ratio
- Cement: 1 part
- Sand: 1 1/2 parts
- Gravel/Stone: 2 parts (3/8-inch)
Why This Ratio?
Using a 1:1 1/2 mix for concrete topping, instead of a 1:3 mix, results in a richer mix. The increased cement content provides:
- Improved Strength: A higher cement content leads to a stronger, more durable topping.
- Enhanced Bonding: Better adhesion to the existing base is achieved with a richer mix.
- Greater Wear Resistance: The topping becomes more resistant to wear and tear.
Important Considerations
- Surface Preparation: Ensure the old base is properly roughened to promote good bonding.
- Thickness: The topping should be at least 1 inch thick to maintain its integrity.
- Gravel/Stone: While not part of the primary cement to sand ratio, the addition of 2 parts of 3/8-inch gravel or stone contributes to the overall strength of the mix.
- Water Content: Be cautious with water content, as excessive water weakens the final structure.
Example:
If you are mixing 1 bucket of cement, you would need to add 1 1/2 buckets of sand and 2 buckets of 3/8-inch gravel/stone. The amount of water will be determined by how the mix looks; it should be easy to handle and place but not too wet.
