Plywood Waterproofing: What You Should Know?

Written By Adam Paul - Waterproofing Expert

Waterproof plywood is a wood material that combines waterproofing membrane and plywood. A waterproofing layer is applied to the plywood to add waterproofing capability due to plywood is not a fully waterproof material. The most used waterproofers on plywood are seals, paints, epoxy, waterproofing stains, and plastic sheeting.

Marine plywood has a higher water resistance capability among plywood types such as BC, OSB, Hardwood, MDF, and RTD types. Weatherproof plywood is considered as exterior plywood, which is prone to more water.

A waterproof plywood can prevent warping, delamination, swelling, growth of mold and mildew, and rotting the plywood. The advantages of plywood waterproofing are it can resist water damage, prevent mold and mildew, improve durability, protect against stains, maintain strength, and prevent swelling even it is exposed to water.

You should follow a proper step by step guide with suitable tools, materials, and safety instruments to waterproof plywood. The durability of the waterproofed plywood depends on the waterproofing method used and the condition of the plywood exposed to. The most durable plywood waterproofing method is epoxy waterproofing, which can last more than 8 years.

Plywood waterproofing does not directly affect its strength. When the plywood is flexible too much, its waterproofness will be lost due to cracks and damage in the layer. After plywood is applied on the surface, it is more resistant to moisture, rotting, decay, chemicals, insects and fire.

You should protect waterproof plywood by preventing overbending, exposure to chemicals, higher temperature fluctuation, and cutting and drilling the surface as it damages the waterproofing layer.

Is Plywood Waterproof?

Plywood is not a completely waterproof material, but it can resist water to a certain extent. It can warp, rot, swell, and develop mold and mildew when it is exposed to water over time. The most water resistant plywood type is marine plywood. Other plywood types have a lower water-resistant capability than that. In order to fully waterproof plywood you should apply sealers, paints, epoxy, waterproofing stains and plastic sheeting on the plywood surfaces and edges.

Read More: What to Know About Deck Waterproofing?

What are the Weatherproof Plywood?

Weatherproof plywood is considered as exterior plywood. These are designed to withstand outdoor weather conditions such as higher humidity and moisture. In order to withstand higher humidity, these plywoods were bonded together using phenolic resin.

These are the 6 most weatherproof plywood types

1. Marine grade plywood
2. Pressure-treated plywood
3. Structural plywood
4. Baltic birch plywood
5. Medium Density Overlay (MDO) plywood
6. High Density Overlay (HDO) plywood

What are the Advantages of Plywood Waterproofing?

The advantages of plywood waterproofing are it can resist water damage, prevent mold and mildew, improve durability, protect against stains, maintain strength and prevent swelling even it is exposed to water.

Resistant to water damage: Once plywood is waterproofed, it becomes resistant to water damage. As a result of this it won't warp, delaminate, or rot even when exposed to water.

Prevent mold and mildew: Plywood waterproofing can prevent the growth of mold and mildew in the plywood. It not only damages the plywood but can also cause health problems to the users.

Enhanced durability: Plywood waterproofing enhances the durability of plywood, making it last longer, even when used in damp or wet conditions.

Protect against stains: Waterproofed plywood is resistant to staining. This means that it can maintain its appearance even when exposed to water.

Maintain the strength: Plywood waterproofing helps to maintain the strength of plywood. This makes it suitable for a wider range of applications.

Prevent swelling: Plywood waterproofing prevents swelling when it is exposed to water. It helps to maintain its size and shape.

What Plywood Problems Fix After Waterproofing?

After plywood is protected by waterproofing, its problems due to moisture, humidity and water, such as warping, delamination, mold and mildew growth, staining and swelling, can be fixed successfully.

How to Waterproof Plywood?

Waterproofing plywood can significantly extend its lifespan. Here are the steps you can follow:

Materials for the Plywood Waterproofing

1. Plywood
2. Waterproofing sealer (like sealant, latex paint, or oil-based stain)
3. Sandpaper (80-grit and 220-grit)
4. Paintbrush
5. Clean, dry cloth
6. Water
7. Mild detergent
8. Protective gloves and eyewear

Read More: How to Waterproof the Balcony Floor? – Wood and Concrete

6 Steps Guide for Plywood Waterproofing

1. Clean the plywood: Before you begin the waterproofing process, it’s essential to clean the plywood surface. Remove any dirt or dust using a mild detergent and water. Rinse the plywood thoroughly and let it dry completely.
2. Sand the plywood: Using 80-grit sandpaper, sand the surface of the plywood. This helps to remove any rough spots and makes the plywood more receptive to the sealer. After sanding, wipe down the plywood with a clean, dry cloth to remove any dust.
3. Apply the first coat of sealer: Apply a coat of waterproofing sealer to the plywood using a paintbrush. Be sure to cover the entire surface, including the edges.
4. Sand the plywood again: Once the first coat of sealer is completely dry, use 220-grit sandpaper to lightly sand the surface. This will help the next coat of sealer adhere better.
5. Apply the second coat of sealer: Apply a second coat of the waterproofing sealer to the plywood. This will ensure that the plywood is thoroughly protected from water damage.
6. Let the plywood cure: Once you've applied the final coat of sealer, let the plywood cure for several days before using it. This will ensure that the sealer has fully penetrated the wood and dried thoroughly.

How Last Long is a Waterproof Plywood?

The durability of the waterproof plywood depends on the waterproofing method used and the condition of the plywood exposed to. Plywood can be waterproofed by using paint, sealant, epoxy, waterproofing stains, an plastic sheetings. Each of these plywood waterproofing methods can last long, as below.

1. Waterproof paint for plywood can last 1-5 years
2. Waterproof sealant for plywood can last 2-3 years
3. Waterproof epoxy for plywood can last 4-8 years
4. Waterproof stains for plywood can last 1-2 years
5. Waterproof plastic sheeting for plywood can last 3-5 years

Can Plywood Strength Increase After Waterproofing?

Plywood waterproofing does not directly affect its strength. But it protects it from elements without deteriorating moisture, humidity, higher temperature, and UV rays. This will reduce the weaken the plywood over time. Hence plywood waterproofing helps to maintain the plywood strength indirectly.

Can Plywood Waterproofing Reduce its Flexibility?

No plywood waterproofing does not reduce its flexibility. Because waterproofing treatments are designed to penetrate and coat the material, protecting it from moisture regardless of its flexibility. There is a limitation in the waterproofing layer. If the plywood is elongated, than its limited waterproofing layer can be damaged, and waterproofness can be destroyed.

What Resistance Improved after Plywood Waterproofing?

After plywood is waterproofed, it withstands strongly against moisture, rot and decay, insects, mild chemicals, and fire.

1. Moisture resistant: Plywood waterproofing increases its resistance to moisture. This makes the plywood less likely to warp, swell, or rot when exposed to water or high humidity conditions.
2. Rot and decay resistance: Plywood waterproofing helps to prevent the growth of fungi, mold, and other organisms that can cause the wood to rot and decay.
3. Insect resistance: Plywood waterproofing helps to repel insects such as termites and beetles, which are harm to wood in any environmental condition.
4. Chemical resistant: Plywood waterproofing increases the resistance to certain mild chemicals.
5. Fire resistance: Plywood waterproofing treatments can make the plywood more fire resistant.

How to Protect Waterproof Plywood?

Plywood and its waterproofing layer should be protected in order to prevent water damage to the plywood. Plywood waterproofing layer can be damaged due to these ways such as

Prevent overbending: The plywood waterproofing layer can be damaged when it is overbending. Overebding can crack the waterproofing layer on the plywood, and it tends to leak water inside.

Prevent exposure to chemicals: Harsh chemicals like acids can damage the waterproof layer on the plywood. It damages the waterproofing layer on the plywood and tends to leak water inside.

Prevent higher temperature fluctuations: Higher temperature fluctuations can deteriorate and crack the waterproofing layer on the plywood. That causes to leak water inside the plywood.

Do not drill or cut on the surface: Waterproofed plywood can be damaged by cutting and drilling. This causes to engage the plywood with water, which causes many water related problems such as warping, rotting, mold and mildew growth, and swelling.

Is BC Plywood Waterproof?

BC plywood is a type of plywood that has one 'B' grade face and one 'C' grade face. The 'B' grade face is usually a smooth, sanded surface that's suitable for finishing, while the 'C' grade face may have some knots and it is less smooth.

BC plywood is not waterproof. It is more resistant to moisture than other types of plywood.It can warp, rot or develop mold if it is exposed to water or high humidity. You should apply a waterproof sealant if you use it by exposing higher humidity and moisture.

Is OSB Plywood Waterproof?

OSB (Oriented Strand Board) plywood is a type of engineered wood product that's made up of compressed layers of wood strands with adhesives. It is mostly used in residential and commercial construction due to its strength and affordability.

OSB plywoods are not completely waterproof. But it has some degree of water resistance. OSB plywood can swell, warp, and start to disintegrate when is is exposed to water. However some types of OSB has higher water resistance. But those are not waterproof.

Is Marine Plywood Waterproof?

Marine plywood is a type of plywood that is designed to resist rotting in a high-moisture environment. Marine plywood are made from high-quality hardwoods and waterproof glues.

Marine plywood is not a complete waterproof plywood. But it has a higher degree of water resistance. It can withstand more resistance to water than ordinary plywood without warping or losing structural integrity. Marine plywood is highly recommended for environments with higher moisture and humidity.

Is Hardwood Plywood Waterproof

Hardwood plywood is a type of plywood that is made from different species of hardwood, such as oak, maple, or mahogany. Hence, it is used for furniture, cabinetry, and other interior applications.

Hardwood plywood is not waterproof. However, it has some resistance to moisture due to the adhesive used in its manufacturing process. When it is exposed to higher humidity conditions, it can warp, crack, or delaminate over time. Hence, you should not use hardwood plywood for higher moisture tasks.

Is MDF Plywood Waterproof

MDF (Medium-Density Fiberboard), is a type of plywood. MDF boards are made by breaking down hardwood or softwood residuals into wood fibers and combining it with wax and a resin binder by applying high temperature and pressure.

MDF is not a waterproof plywood. Its adhesiveness is loose when it is exposed to water, humidity, and moisture over time. Hence, MDF is not suitable for products that are exposed to higher moisture.

Is RTD Plywood Waterproof?

RTD (Rated Sheathing) is a type of plywood that is made from a combination of hardwood and softwood veneers, which are glued together as layers.

RTD plywood is not completely waterproof, but it has a higher resistance to moisture and humidity. Hence it can be used in wetted areas where it won’t constantly exposed to water and higher humidity. In order to use RTD in higher moisture areas, you should apply waterproof sealant on the RTD.

Can Brick Sealing Prevent Water Damage?

Yes, Brick sealing can prevent water damage by creating a protective barrier on the surface. Sealed bricks repels the water and reduce the risk of structural issues and mold growth on the regular wetting surfaces. The effectiveness of the brick sealing depends on factors like sealant quality, application, and maintenance of the sealant coating.