Wet plywood can lead to issues like warping, swelling, and delamination when exposed to water. While moisture-resistant or waterproof plywood varieties offer higher resistance, prolonged exposure to water can still cause damage. Understanding plywood’s composition and how different types respond to moisture is key to selecting the right type for your project and taking appropriate preventive measures.
The Ply-Weekly Newsletter
Receive a curated roundup of the best in the world of plywood – every two weeks.
Plywood Composition
Plywood is constructed from multiple thin veneer sheets bonded together with adhesive. The quality and type of adhesive play a significant role in the plywood’s resistance to moisture. The adhesive creates a water-resistant barrier that helps prevent water penetration. The degree of moisture resistance varies based on the grade and type of adhesive used.
Adhesives
Interior Adhesives
Interior-grade plywood utilizes urea-formaldehyde glue, which offers limited resistance to moisture. This type of adhesive is suitable for applications where the plywood will not be exposed to high humidity or direct contact with water. Urea-formaldehyde glue is cost-effective and provides sufficient bonding strength for indoor uses such as furniture, cabinetry, and paneling. However, it is prone to breaking down when exposed to moisture, leading to potential delamination and structural weakening. It should be used in dry, controlled environments to ensure its longevity and performance.
Exterior Adhesives
Exterior-grade plywood is bonded with phenol-formaldehyde glue, which is significantly more resistant to water and adverse weather conditions. This type of adhesive creates a robust and durable bond that can withstand prolonged exposure to moisture, making it ideal for outdoor applications. Phenol-formaldehyde glue ensures that the plywood maintains its structural integrity even in challenging environments. It is commonly used in the construction of outdoor furniture, sheds, fences, and even certain marine applications. Its enhanced water resistance and durability make it a reliable choice for projects exposed to the elements.
Types of Plywood and Water Resistance
Interior Plywood
Advantages:
- Cost-effective
- Readily available for indoor projects
Disadvantages:
- Limited moisture resistance
- Not suitable for high-humidity areas or direct water exposure
Designed for indoor use, where exposure to moisture is minimal. It’s commonly used for furniture, cabinetry, and other indoor applications. However, it has limited moisture resistance and can suffer damage if exposed to water. To enhance its longevity:
- Apply sealants to the edges of interior plywood to prevent moisture from seeping in.
- Ensure it is used in environments with controlled humidity to avoid potential water damage.
Exterior Plywood
Advantages:
- Enhanced moisture resistance
- Suitable for outdoor projects
Disadvantages:
- Requires proper sealing and maintenance
- More expensive than interior plywood
Exterior plywood is designed to withstand outdoor conditions and offers enhanced moisture resistance. It’s ideal for projects exposed to the elements, such as sheds, fences, and exterior walls. The use of water-resistant adhesive ensures it can handle more significant moisture exposure compared to interior plywood. Proper sealing and finishing are essential to maintain the water resistance of exterior plywood. Applying water-resistant paint or varnish can further enhance its durability.
Marine Plywood
Advantages:
- Exceptional water resistance
- Resistant to fungi and insects
Disadvantages:
- Higher cost
- May be overkill for non-marine applications
Marine plywood offers the highest level of water resistance, making it suitable for applications involving constant exposure to water, such as boat building. It is made with high-quality veneers and waterproof adhesive, providing excellent resistance to water, fungi, and insects. Ideal for docks, boats, and other marine environments where resilience against water damage is critical, marine plywood’s robust nature ensures it remains structurally sound despite prolonged water exposure.
Preventing and Dealing with Wet Plywood
Preventing Wet Plywood
To prevent moisture damage, store plywood sheets elevated off the ground in a dry, covered area, away from direct exposure to rain or high humidity. Apply sealants to all exposed edges and surfaces, particularly for projects in high-moisture environments. Ensure proper ventilation in storage and application areas to minimize humidity levels.
Dealing with Wet Plywood
To manage wet plywood, promptly identify and dry it using air circulation, fans, or dehumidifiers. Regularly inspect plywood in moisture-prone areas for signs of damage, such as warping or mold growth. Replace any plywood showing significant damage to maintain structural integrity, as warped or delaminated plywood can compromise the stability and safety of the project.