For repointing mortar joints, a common and often recommended ratio is 4:1.
Most builders recommend a mortar mix of a 4:1 ratio if you're repointing at a depth of 10mm. This ratio refers to the proportion of sand to cement.
Understanding the 4:1 Mortar Mix Ratio
The 4:1 ratio is a widely used guideline for repointing, particularly for standard residential brickwork where the depth of the joint is around 10mm. Here's what the numbers typically represent:
- 4 Parts Sand: This is usually sharp sand or a specific mortar sand suitable for repointing. The type and colour of the sand significantly impact the final appearance of the mortar.
- 1 Part Cement: This refers to Portland cement, which acts as the binder. The strength and durability of the mortar depend heavily on the correct amount of cement.
Using the correct ratio is crucial for creating a mortar that is durable, weather-resistant, and compatible with the existing brickwork. Too much cement can make the mortar too strong and rigid, potentially causing damage to the softer bricks over time. Too little cement can result in a weak, crumbly mortar that won't last.
Why Depth Matters (10mm Example)
The reference specifically mentions the 4:1 ratio being suitable for a 10mm repointing depth. While 4:1 is a good starting point for many typical applications, slight variations in ratios might be considered depending on:
- The type and age of the existing mortar (matching the original strength is often key).
- The type of brick being used.
- Exposure to weather conditions.
- The depth of the raked-out joint.
However, based on common recommendations and the provided reference, the 4:1 sand-to-cement ratio is a standard and recommended mix for repointing at a depth of 10mm.
Simple Ratio Table
Here’s a basic breakdown of the components based on the 4:1 ratio:
| Component | Proportion (Parts) |
|---|---|
| Sand | 4 |
| Cement | 1 |
Remember, this is a ratio by volume, not weight. Accurate measurement is important for consistent results. Always ensure the sand is clean and free from contaminants.
Using the recommended 4:1 ratio helps ensure the new mortar performs correctly and blends well with the existing structure.
