The most commonly used timber sizes for shuttering are 15mm or 18mm.
Timber shuttering, often made from plywood or sometimes solid timber planks, is a crucial temporary structure used to hold wet concrete in place until it cures and can support itself. The required strength and stiffness of the shuttering determine the appropriate timber thickness and supporting framework.
Common Shuttering Timber Thicknesses
While various thicknesses can be used depending on the specific application and supporting structure, the reference highlights the most typical sizes:
- 15mm
- 18mm
These thicknesses provide a good balance of rigidity and manageability for many standard concreting tasks.
Why Timber Type Matters
Beyond just thickness, the type of timber product used is equally important, especially given the conditions shuttering is exposed to.
Weather and Boil Proof (WBP)
According to the reference, WBP (Weather and Boil Proof) plywood is particularly preferred for shuttering.
- Reason: WBP plywood is specially manufactured with adhesives that are highly resistant to moisture.
- Benefit: This makes it less prone to delaminating when in contact with wet concrete and exposed to outdoor weather conditions. Delamination can compromise the integrity of the shuttering and the final concrete finish.
Using WBP plywood ensures the formwork remains stable and maintains its shape throughout the curing process.
Factors Influencing Size Selection
While 15mm and 18mm are common, the optimal size can depend on several factors:
- Concrete Pressure: Deeper or larger pours exert more pressure on the formwork, potentially requiring thicker timber or more robust support.
- Support Spacing: Closer spacing of supporting battens or frames allows for thinner timber sheeting. Wider spacing requires thicker, stiffer sheeting to prevent bulging.
- Desired Finish: The surface finish of the timber directly impacts the concrete surface. Smooth, durable sheets like faced plywood are often chosen for visible concrete.
- Reuse: Thicker, higher-quality timber or plywood (like WBP) is more durable and better suited for multiple reuses on different projects.
| Common Thickness | Preferred Type | Key Advantage for Shuttering |
|---|---|---|
| 15mm | WBP Plywood | Good balance of strength/cost for many uses |
| 18mm | WBP Plywood | Increased stiffness, better for wider supports |
| Various | WBP Plywood | Resists delamination in wet concrete/weather |
In summary, when considering timber for shuttering, focusing on 15mm or 18mm WBP plywood is a standard and reliable choice due to its common availability, appropriate strength, and resistance to the harsh, damp environment of concrete work.
