The maximum thickness of sand and cement render generally recommended is 25mm.
According to general guidelines, the thickness of a cement render coat typically falls between 6 and 25mm. This range is influenced by several factors, including the specific type of application, the nature of the surface being rendered, and the desired final appearance.
Understanding Render Thickness
While 25mm is the upper limit for standard, general applications as stated in the reference, it's important to note that for heavier-duty uses, particularly on external walls exposed to more severe conditions, a thicker render layer can be applied. The reference mentions this possibility, indicating that while 25mm serves as a common maximum for typical jobs, specific project requirements might necessitate exceeding this for enhanced durability or flatness correction over irregular surfaces.
Factors Influencing Render Thickness
The optimal thickness isn't a one-size-fits-all rule. Key elements that determine how thick the render should be include:
- Application Type: Internal vs. External walls, structural vs. decorative finishes.
- Surface Condition: Highly uneven or poor-quality substrates require thicker render to achieve a flat surface.
- Desired Finish: Some finishes might require a specific minimum or maximum thickness.
- Number of Coats: Render is often applied in multiple layers (scratch coat, float coat, finish coat), with each layer contributing to the overall thickness. The scratch coat, applied first, might be thicker to level the wall, while subsequent coats are thinner.
| Application Type | Typical Thickness Range (General) |
|---|---|
| General Render | 6mm - 25mm |
| Heavy-Duty/External | Potentially thicker than 25mm |
It's crucial to apply render in appropriate thicknesses per coat to prevent issues like cracking, delamination, or slumping. Applying a single, excessively thick layer is generally discouraged. Building standards and manufacturer guidelines should always be consulted for specific projects.
