A Guide to Sealing & Waterproofing Plywood

Plywood is a popular material in both construction and crafting due to its versatility and cost-effectiveness. However, its susceptibility to moisture can lead to deterioration over time if not properly protected.

Waterproofing and sealing plywood are essential practices for enhancing its durability and ensuring it performs well in moisture-prone environments. In this guide, we’ll be exploring the various methods used to seal and waterproof plywood, ensuring it remains durable and functional regardless of the setting.

Is Plywood Waterproof?

Plywood is not waterproof. This engineered wood is made from layers of wood veneer bonded together with adhesives. While these adhesives are moisture-resistant to some degree, the wood itself can absorb water if not adequately treated. When plywood absorbs water, it can swell, warp, and eventually weaken, which compromises its structural integrity.

The capacity of plywood to resist moisture depends heavily on its grade and the type of adhesive used during its manufacturing. For instance, exterior-grade plywood, made with waterproof adhesives, can handle moisture better than interior-grade plywood.

Why Seal and Waterproof Plywood?

Sealing and waterproofing plywood are critical processes that prevent water absorption, extending the material's lifespan and usability in various applications. For projects exposed to the elements, such as outdoor furniture, decking, or siding, waterproofing is essential to prevent decay and fungal growth.

Even in indoor settings, areas like bathrooms and kitchens can expose plywood to humidity and splashes, making moisture resistance a valuable precaution.

Through sealing and waterproofing, plywood can maintain its shape and strength over time, making it more effective and safe for use in a range of projects. This treatment not only enhances the plywood's durability but also adds to its aesthetic appeal by preventing unsightly water stains and damage.

This introduction and exploration into the moisture-related properties of plywood set the stage for further discussion on specific sealing and waterproofing techniques that can protect and preserve plywood in environments where moisture is a concern.

Preparing Plywood for Sealing and Waterproofing

Before applying any sealant or waterproofing treatment, it's important to properly prepare the plywood to ensure the protective coatings adhere effectively and perform as expected. Here are the steps to prepare plywood for waterproofing:

Cleaning

Start by cleaning the plywood to remove any dust, dirt, or grease. Use a dry cloth or brush to wipe down the surface thoroughly. If there are stubborn stains, a damp cloth with a mild dish soap can be used, but make sure the plywood dries completely afterwards.

Sanding

Sand the plywood surface with medium-grit sandpaper (about 120 to 150 grit) to smooth out any rough areas and to open up the pores of the wood, which helps the waterproofing agent to penetrate deeper. Sand in the direction of the grain to avoid scratches that could impair the finish.

Dust Removal

After sanding, it's important to remove all the sanding dust, as leftover particles can hinder the adhesion of the sealant. A vacuum cleaner followed by a tack cloth is effective for ensuring a clean surface.

Edge Treatment

Plywood edges are more porous and therefore more susceptible to water damage. Treat the edges with particular care, ensuring they are smooth and clean.

Application of a Primer (Optional)

Depending on the type of waterproofing product used, applying a primer might be necessary to ensure optimal adhesion and sealing performance.

These preparation steps are essential for effective waterproofing and will help extend the life of the plywood, maintaining its structural integrity and appearance.

Sealing Plywood

How to Seal Plywood

Sealing plywood is an effective way to protect it from moisture and extend its life. Here’s a general guide on how to seal plywood:

Select the Right Sealant

Choose a sealant appropriate for the intended use of the plywood. For exterior use, make sure the sealant is suitable for outdoor conditions, providing UV protection and water resistance. Polyurethane, lacquer, or epoxy resin are good options.

Application

Apply the sealant using a clean brush, roller, or sprayer, depending on the product instructions. Apply a thin, even coat and make sure to cover the entire surface, including edges.

Drying Time

Allow the first coat to dry as per the manufacturer's instructions. The drying time can vary based on the type of sealant and the environmental conditions.

Second Coat

Apply a second coat to ensure complete coverage and additional protection. This is particularly important for plywood that will be used outdoors or in moisture-prone areas.

Curing

Allow the sealant to cure fully before using the plywood. Curing time can vary, but it is critical for achieving the full strength and waterproof properties of the sealant.

Sealing Plywood Edges

The edges of plywood are particularly vulnerable to moisture due to their higher porosity. Here are special considerations for sealing them:

Apply a Thicker Layer

Edges may absorb more sealant, so apply a thicker layer or additional coats to ensure they are fully protected.

Use Edge Banding

For a more finished look and added protection, consider applying edge banding to the plywood edges. This thin material can be ironed on and trimmed to fit, sealing the edges against moisture effectively.

Regular Inspection and Maintenance

Edges are prone to wear and tear, so regular checks and touch-ups on the sealant can help maintain the integrity of the plywood.

By following these detailed steps, you can effectively seal plywood, enhancing its durability and resistance to moisture, ensuring it performs well for years in various applications.

How to Waterproof Plywood

Waterproofing plywood is essential for ensuring its longevity, especially in environments where it is exposed to moisture. Here are detailed steps on how to effectively waterproof plywood:

Choose the Right Waterproofing Product

Select a waterproofing product suitable for plywood, such as epoxy sealant, polyurethane, or an acrylic-latex paint. Each of these products can provide a strong, waterproof layer.

Prepare the Surface

Ensure the plywood is clean, dry, and smooth. Sand any rough areas and wipe down the surface to remove dust and debris.

Apply the Waterproofing Agent

Use a brush, roller, or sprayer to apply the waterproofing product evenly across the surface of the plywood. Pay special attention to the edges, which are more susceptible to water damage.

Allow to Dry

Follow the product’s instructions for drying times. Ensure the first coat is completely dry before applying additional coats if necessary.

Apply Additional Coats

Depending on the exposure of the plywood to moisture, multiple coats might be necessary to ensure complete waterproofing.

Cure the Waterproofing

Allow the final coat to cure completely, according to the manufacturer's instructions, to ensure the best protection.

Finishing Treatments for Plywood

Can You Varnish Plywood?

Varnishing is not only a viable option but a recommended finish for plywood used in less moisture-prone environments. Varnish can enhance the appearance of plywood while providing a protective layer that resists dirt and light moisture.

Sealing and Waterproofing Plywood FAQs

Can plywood be made completely waterproof?

While plywood cannot be made entirely waterproof, it can be treated to become highly water-resistant. The degree of waterproofing achievable depends on the type of plywood, the quality of the waterproofing materials used, and the application process.

For maximum protection, it is crucial to apply a high-quality epoxy or polyurethane sealant that penetrates deep into the plywood layers and seals any gaps. Multiple coats may be required to build up a sufficient barrier against moisture. Additionally, maintaining the sealant by applying fresh coats periodically can extend the lifespan and effectiveness of the waterproofing.

How often should plywood be resealed or waterproofed?

The frequency for resealing or re-waterproofing plywood depends on several factors, including the type of sealant used, the environmental conditions to which the plywood is exposed, and the level of wear and tear it experiences. As a general guideline:

• Exterior plywood used outdoors should ideally be inspected and resealed every 1 to 3 years.
• Interior plywood in damp areas like bathrooms and kitchens may require attention every 3 to 5 years.
• Regular inspections for any signs of water damage, such as swelling or discoloration, can help determine the right time to reapply a waterproof coating.

What are the best products for sealing and waterproofing plywood?

The best products for sealing and waterproofing plywood often vary depending on the specific requirements of the project and the environmental conditions. Here are some top-rated options:

• Polyurethane Sealants: Excellent for both indoor and outdoor use, polyurethane provides a durable and clear finish that protects against moisture and UV radiation.
• Epoxy Sealers: Known for their robust waterproofing capabilities, epoxy sealers are ideal for areas that are continuously exposed to water.
• Acrylic-Latex Sealants: These are cost-effective and easy to apply, making them a good choice for large projects where budget constraints are a concern.
• Marine Varnish: Especially useful for marine applications or areas with high moisture exposure, marine varnish can add a layer of protection that also enhances the aesthetic appeal of the wood.

Choosing the right product depends on balancing the specific needs of your project with the environmental challenges it will face. Always follow the manufacturer's application guidelines for the best results.