Plywood is an engineered wood panel made from thin layers of wood veneer glued together. The grain of each layer is perpendicular to the adjoining layers, giving the panel strength and stability. There are four main types of plywood recognised under Australian standards: Marine, Exterior, Interior, and Structural. The type of plywood is determined by the timber species, veneer grade, and glue type used.

Timber Species

Common plywood timber species include:

• Australian Plywood: Hoop pine (Araucaria Cunninghamii), Radiata pine
• Imported Plywood: Mixed tropical hardwoods, Gaboon, Meranti, Russian Birch

Veneer Grades

Veneers are graded by letter, from A (highest quality) to D (lowest quality).

• A Grade: High-quality appearance grade, with no knots, holes, patches, or unnatural discolouration. (Read more)
• B Grade: Appearance grade for high-quality paint finishing. (Read more)
• C Grade: Non-appearance grade with a solid surface.
• D Grade: Non-appearance grade with permitted open imperfections.

Glue Types

• Phenolic formaldehyde resin: This is the most common adhesive, suitable for marine, structural, and exterior plywood. It achieves the highest bond rating (A bond) and performs well in moist environments.
• Melamine urea resin: This is typically used in appearance-grade plywood for internal applications. It is transparent when set, making it suitable for showcasing natural veneer.

It is recommended to choose plywood with low formaldehyde emission ratings, such as E0 (E zero) and Super E0.

Australian Plywood Standards

Australian and New Zealand plywood standards are known for their high quality.

• Marine plywood (AS/NZS 2272): The highest quality standard, made only with 'A' quality veneers and designated marine species. It uses a waterproof A-bond glue.
• Structural plywood (AS/NZS 2269): Constructed with an A-bond glue and veneers that meet specific stress grades.
• Exterior plywood (AS/NZS 2271): Must use an A-bond glue and a mix of veneer grades compliant with the standard. Typically used in applications where moisture may be present but a structural rating is not required.
• Interior plywood (AS/NZS 2270): Uses a non-structural glue and is suitable for interior applications where there is no moisture or structural requirements.

Quality Assurance

The Engineered Wood Products Association of Australasia (EWPAA) ensures the quality of engineered wood products in Australia. They provide quality control and product certification, including bond and stress tests.

Sustainability

The leading wood certification scheme in Australia is Responsible Wood, which is endorsed by the Programme for the Endorsement of Forest Certification (PEFC). This scheme ensures that wood products are legally and sustainably sourced. Consumers can rely on this certification to ensure the sustainability of their plywood choices.

Common Pitfalls of Cheap Alternatives

Imported plywood may have issues such as:

• Delaminating plywood: Despite claiming to be A-bond, some imported plywood may experience bond failure when exposed to moisture.
• Sub-standard core: The core may be made from juvenile trees or non-durable species, resulting in poor structural properties.
• Thin face veneers: Some imported plywood has very thin face veneers, which can cause structural issues and make finishing difficult.

Protective Coatings

Protective coatings are crucial for preserving the appearance and durability of plywood.

• Water-based coatings: These are common due to their ease of use, consistent finish, and non-yellowing properties.
• Oil-based coatings: These penetrate deep into the timber, preserving the grain and repelling moisture. However, they can significantly alter the timber's appearance.
• Powder-coated and UV-cured finishes: These offer the highest level of surface hardness but can be difficult to apply and maintain.

It is recommended to seal plywood on all sides (face, back, and edges) to prevent moisture damage and maintain flatness. Factory-finished panels offer greater consistency and are often supplied with a warranty.  (Read more)

Fixing Systems

Plywood can be fixed using screws or concealed fixing systems. When choosing a fixing system, it is important to ensure compatibility with the panel warranty. (Read more)

Fire Ratings

Most untreated plywood panels comply with Group 3 fire rating. Alterations to the panel, such as perforations or slotting, can affect the fire performance and require further testing.

Fire Retardant Treatments and Coatings

• Intumescent coatings: These swell when exposed to heat, creating a barrier that starves the fire of oxygen. However, they can be expensive, have a substandard finish, and require yearly inspections.
• Fire retardant impregnated panels: These panels are treated with a fire retardant, but may have issues with delamination, discolouration, and low durability.

When specifying plywood, it is crucial to consider factors such as the intended application, required durability, and aesthetic preferences. By understanding the different types, standards, and potential pitfalls, one can make informed decisions and ensure the successful use of plywood in various projects.