Plywood is one of the most popular subflooring materials for flooring finishes such as laminate, vinyl , hardwood flooring and carpets. At the same time, plywood flooring is also an cost-effective floor covering option.
The main worry for homeowners is whether water will damage plywood.
The answer is Yes; water will damage plywood if it gets wet for an extended period of time. Plywood can absorb water, especially if it is not adequately sealed or protected. When exposed to water or high humidity, plywood then swells, warp, and eventually delaminates, leading to structural weakness and damage. After swelling, the plywood begins to lose its shape and eventually the plywood layers start separating resulting to cracking.
Why does plywood get wet?
The main reason why plywood gets wet and absorbs is because it is an absorbent material.
Plywood is a composite material made by bonding together several layers of thin wood veneers with adhesives.
These layers are usually arranged with the grain direction of adjacent plies perpendicular to each other, which enhances the plywood’s strength and stability. The combination of different wood layers gives plywood its characteristic strength and flexibility.
However, being composed of multiple wood layers, plywood contains small voids or gaps between these layers. These voids are known as pores, and they are responsible for making plywood a porous material. These pores allow air and moisture to penetrate into the plywood.
Because of its porous nature, plywood has the ability to absorb water to some extent.
When plywood is exposed to moisture, such as in humid conditions or when it comes into contact with water, the moisture can penetrate the small voids between the wood layers and get absorbed into the plywood.
This absorption causes the plywood to swell as it takes in water.
How long does it take for water to damage plywood?
If plywood is exposed to wetness for a short period of time, it can still be dried out and maintain its structural strength. However, prolonged exposure to pools of stagnant water or rain can cause delamination of the plywood layers.
At the same time, the time it takes for water to damage plywood can vary significantly depending on several factors, such as:
- Type of plywood,
- Its exposure to water,
- Environmental conditions,
- The overall quality of the plywood
Here are some key factors that influence how quickly water can damage plywood:
1.Type of plywood:
Different types of plywood have varying levels of water resistance.
Standard plywood:
Standard plywood, often referred to as interior plywood or CDX plywood, is the most common type of plywood used for general indoor construction, such as in walls, roofs, and subfloors.
While it can handle some moisture exposure, it is not designed to withstand prolonged contact with water or direct outdoor exposure.
Standard plywood typically has fewer layers and may contain voids between the plies, making it more susceptible to water absorption and damage.
When standard plywood gets wet, it can start to swell, warp, and weaken.
Its structural integrity may be compromised, and it can become more prone to delamination, where the layers start to separate. Continuous exposure to water can cause the plywood to break down and deteriorate over time.
Marine-grade plywood:
Marine-grade plywood is specifically manufactured to be highly resistant to moisture and water.
It is designed for use in marine environments, such as boat construction, docks, and other outdoor applications where the plywood will be exposed to water, humidity, and harsh conditions.
Characteristics of marine-grade plywood that make it water-resistant include:
- High-quality wood: Marine plywood is typically made from durable wood species, such as Douglas fir or Okoume, that have natural resistance to decay and moisture.
- Thicker veneers: Marine-grade plywood usually has thicker veneers, reducing the number of voids and gaps in the plywood, which enhances its water resistance.
- Exterior glue: The adhesive used to bond the layers in marine-grade plywood is a waterproof or fully waterproof glue. This type of glue ensures that the layers remain securely bonded even when exposed to water.
- Special manufacturing process: Marine-grade plywood undergoes a rigorous manufacturing process to ensure its water-resistant properties. This may include higher quality control standards and additional treatments.
When marine-grade plywood gets wet, it is less likely to swell, warp, or delaminate compared to standard plywood.
It can handle extended exposure to water without significant damage and is more durable in humid or wet environments.
If you anticipate exposure to water or high humidity, choosing marine-grade plywood can provide better protection and longevity for your project.
2. Duration of water exposure:
The longer plywood is exposed to water, the higher the likelihood of damage.
Continuous exposure to water or prolonged contact with moisture can lead to significant swelling, warping, and delamination of the plywood
3. Environmental conditions:
High humidity, rain, and damp environments can accelerate the water absorption process in plywood, potentially leading to quicker damage
High humidity:
Humidity refers to the amount of moisture present in the air. When the air is humid, it contains a high concentration of water vapor.
Plywood is hygroscopic, which means it can absorb and release moisture depending on the surrounding humidity levels.
- In high humidity environments, plywood tends to absorb moisture from the air, leading to swelling and warping. This can be a concern in regions with consistently high humidity, such as tropical or coastal areas.
- Plywood used in indoor spaces with high humidity, such as bathrooms or basements, is also at risk of water absorption from the surrounding air.
Rain:
Rainfall is a significant source of water exposure for outdoor plywood applications. When plywood is exposed to rain, the water can penetrate its porous structure.
- If the plywood is not properly sealed or protected, rainwater can be absorbed into the plywood, leading to swelling, warping, and potential delamination.
- Repeated exposure to rain and wetting-drying cycles can compound the damage, particularly if the plywood does not have a chance to dry out fully between rain events.
Damp environments:
Any area with constant or frequent moisture presence can be considered a damp environment. This includes places like basements, crawl spaces, and areas with poor ventilation.
- In damp environments, plywood can readily absorb moisture from the surroundings, especially if it comes into direct contact with damp surfaces or soil.
- Lack of airflow and sunlight in damp spaces inhibits the drying process, making it challenging for the plywood to release the absorbed moisture effectively.
4.Plywood protection:
If the plywood is properly sealed, coated, or treated with water-resistant products, it can withstand water exposure for a longer time before showing signs of damage
Here’s a more detailed explanation of how these protective measures work:
Sealing:
Sealing plywood involves applying a layer of protective material, such as a sealant or primer, to the surface and edges of the plywood.
The sealant creates a barrier that prevents water from easily penetrating the plywood’s porous structure. It effectively reduces the plywood’s ability to absorb moisture and minimizes the risk of swelling, warping, and delamination.
There are different types of sealants available, including oil-based, water-based, and polyurethane-based sealers. Water-based sealers are often preferred for indoor use because they have lower VOC emissions and are generally easier to clean up.
Oil-based sealers, on the other hand, tend to be more durable and provide better water resistance for outdoor applications.
Coating:
Coating plywood involves applying a layer of waterproof or water-resistant material on the plywood’s surface. Coatings are typically thicker and more durable than sealants, providing additional protection against water exposure.
The coating forms a physical barrier that prevents water from seeping into the plywood and causing damage.
Epoxy coatings are commonly used for waterproofing plywood, especially in applications where high water resistance is required.
Epoxy coatings create a strong, impermeable layer that is effective in marine and outdoor environments.
Treating with water-resistant products:
Treating plywood with water-resistant products involves impregnating the plywood with chemicals or preservatives that repel water and inhibit decay.
Pressure-treated plywood is a common example of this approach. It undergoes a process where it is infused with water-resistant chemicals under high pressure, making it more resistant to water, rot, and insect damage.
5. Plywood quality:
Higher-quality plywood with well-bonded layers and fewer voids offers better protection against water-related issues compared to lower-quality plywood.
Let’s explore this further:
Well-bonded layers:
Higher-quality plywood is manufactured using a meticulous process that ensures the layers, or plies, are well-bonded together. This means that the adhesive used to bond the layers is evenly distributed and firmly holds the plies in place. Well-bonded layers create a strong and stable plywood structure, making it less prone to delamination when exposed to moisture.
In contrast, lower-quality plywood may have uneven or weak bonds between the layers. This can lead to separation between the plies when the plywood absorbs water, resulting in a loss of structural integrity and increased susceptibility to water damage.
Fewer voids:
Voids, or gaps, are empty spaces between the wood layers in plywood.
Higher-quality plywood is manufactured with fewer voids, reducing the number of openings through which water can penetrate the material.
Plywood with fewer voids offers better protection against water absorption, as there are fewer paths for moisture to seep into the plywood’s interior.
On the other hand, lower-quality plywood may have more significant gaps, making it easier for water to enter and potentially cause damage.
Grading standards:
Plywood is graded based on its appearance, structural performance, and overall quality. Different grades of plywood have varying levels of water resistance.
- A higher-grade plywood, such as A-grade or B-grade, generally has fewer defects and voids, making it more resistant to water damage.
- Lower-grade plywood, like C-grade or D-grade, may have more imperfections, knots, and voids, which can make it more vulnerable to water absorption and damage.
Water-resistant treatments:
Some higher-quality plywood may receive additional water-resistant treatments during manufacturing or after production.
These treatments can enhance the plywood’s ability to withstand water exposure and reduce the risk of damage.
It’s important to note that even higher-quality plywood is not completely impervious to water damage.
Proper sealing and protection are still necessary to safeguard plywood from long-term water exposure.
Besides, the specific application and environmental conditions also play a significant role in determining the plywood’s performance over time.
How long can plywood be rained on?
The duration of time plywood can be rained on without significant damage depends on several factors, such as the type of plywood, its quality, and the severity of the rain.
In general, standard plywood may start showing signs of water damage, such as swelling and warping, after just a few hours or days of continuous exposure to heavy rain.
In contrast, Marine-grade plywood, designed to resist water, can withstand rain for longer periods, but even then, prolonged exposure can lead to eventual damage.
It is crucial to protect plywood from extended exposure to rain by using appropriate sealants, coatings, or coverings, and to promptly dry the plywood if it does get wet to minimize potential damage.
Regular maintenance and inspection can also help identify any water-related issues early on, ensuring the plywood’s longevity.
Can you use plywood in wet areas?
Yes, plywood can be used in wet areas, but it requires proper protection and treatment to withstand moisture.
For wet environments, it is essential to use marine-grade plywood or pressure-treated plywood, as they are designed to be more water-resistant and decay-resistant.
Additionally, plywood should be sealed or coated with waterproof products to create a barrier against water absorption.
Regular maintenance and proper installation, along with good ventilation, are also crucial to prevent water damage in wet areas where plywood is used.
What type of plywood is okay to get wet?
Marine-grade plywood is the best for use in wet areas. This type of plywood is specifically designed to withstand exposure to water and moisture.
It is the most suitable type of plywood for wet environments and outdoor applications where the plywood will come into contact with water.
Marine-grade plywood is made with durable wood species and bonded with waterproof adhesive, providing superior water resistance and protection against decay.
It is commonly used in boat construction, docks, and other marine or wet environments where standard plywood would not hold up well.
How can I protect plywood outdoors?
To protect plywood outdoors, follow these step-by-step processes:
- Choose the right type of plywood: Opt for marine-grade plywood or pressure-treated plywood, as they are specifically designed to resist water, decay, and insects, making them more suitable for outdoor use.
- Prepare the plywood surface: Ensure the plywood surface is clean and free from dust and debris. Sand the plywood lightly to create a smooth and even surface for better adhesion of protective coatings.
- Apply a waterproof sealant: Use a brush, roller, or sprayer to apply a waterproof sealant to the entire surface of the plywood. Ensure even coverage, and follow the manufacturer’s instructions regarding drying times and the number of coats required.
- Coat with marine varnish or epoxy resin: For additional protection, apply a marine-grade varnish or epoxy resin coating over the sealed plywood surface. These coatings create a strong barrier against water and UV damage.
- Seal edges and joints: Pay special attention to sealing the edges and joints of the plywood with silicone sealant or waterproof tape to prevent water from seeping into these vulnerable areas.
- Elevate the plywood: Whenever possible, elevate the plywood off the ground using blocks or spacers to avoid direct contact with water or moisture on the surface below.
- Cover the plywood: Use a waterproof tarp or cover to protect the plywood during heavy rain or harsh weather conditions. This helps minimize water exposure and prolongs the life of the plywood.
- Regularly inspect and maintain: Periodically inspect the plywood for signs of wear or damage. Touch up any worn areas with additional sealant or coating as needed to maintain its water resistance.
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