how to waterproof plywood

How To Waterproof Plywood (5 Steps & Methods)

Imagine you’ve just finished completing a beautiful outdoor project using plywood. It’s been stained and sealed, and it looks absolutely fantastic. Just when you thought your outdoor furniture or project you completed was ready for anything, it starts to rain. What a nightmare right? This is exactly why you need to know how to waterproof plywood.

There are 5 important steps involved in waterproofing plywood: use a wood filler, sand the plywood, use a primer, use a waterproofing sealer, and re-coating the sealer an additional time. If you follow these steps correctly, your plywood will be fully waterproofed and ready to withstand the outdoor elements.

In this article, we’ll go through each of the steps to waterproofing plywood, so that you can get your deck or other plywood projects ready for rain or snow, or hail.

5 Steps on How to Waterproof Plywood for Outside

As we mentioned earlier, there are five key steps involved in waterproofing plywood. Let’s take a look at each of these steps in a little more detail.

1) Use A Wood Filler

Sometimes, plywood can develop small cracks or holes. These need to be filled in before you can waterproof the plywood. Otherwise, water will just seep right into these cracks and cause damage.

To fill in these cracks and holes, use a wood filler. Now, what is a wood filler? It’s a kind of wood by-product (usual sawdust) that’s mixed with water or a petroleum-based binder to create a putty-like substance. Once this wood filler is applied to the cracks and holes, it will harden and prevent water from seeping through.

Once you’ve applied a wood filler to your plywood, you can move on to the next step.

2) Sand The Plywood

After you’ve used a wood filler to fill in any cracks or holes, the next step is to sand the plywood. This will help to create a smooth surface for the waterproofing sealer applied later on.

sanding plywood

To sand the plywood, you’ll need to use a palm or a hand sander. Start with coarse grit sandpaper and then move on to finer grit sandpaper. Once you’re done sanding, wipe down the plywood with a damp cloth to remove any dust particles. You don’t want any dust or dirt stuck to the plywood when you’re ready to apply a sealer or a finish!

3) Use A Primer

After you’ve sanded the plywood and cleaned off the sawdust, the next step is to use a primer. The purpose of using a primer is to help the waterproofing sealer or finish adhere better to the plywood’s surface.

When choosing a primer, make sure to select one that’s specifically designed for use on plywood. This will ensure that the primer adheres properly and doesn’t cause any damage to the plywood itself.

Applying a primer itself is pretty straightforward. Simply use a rag or a paintbrush to apply an even layer of primer over the entire surface of the plywood (make sure you apply the primer in the direction of the grain!). A few minutes after you’ve applied the primer, wipe off any excess primer that hasn’t been absorbed by the plywood.

And that’s it! Once you’ve applied a primer, move on to the next step.

4) Apply A Waterproofing Sealer or Finish

Now it’s time to apply a waterproofing sealer or finish to your plywood. This will help create a barrier that will prevent water from seeping into the plywood and causing damage.

There are a few different types of waterproofing sealers and finishes that you can choose from. You have epoxy, polyurethane, and even paint! We’ll be covering each of these choices and more later on in the article. But for now, let’s take a look at how to apply any waterproofing sealer or finish.

To apply a waterproofing sealer or finish, use a brush or roller. Start by applying the sealer or finish to the edges of the plywood first and then work your way in towards the center. Make sure that you apply an even layer of sealer or finish and don’t miss any spots!

Once you’ve applied a waterproofing sealer or finish to the plywood, you can move on to the last step.

5) Recoat The Sealer

You might think that a single layer of waterproofing sealer or finish is enough to protect the plywood. But in reality, it’s always a good idea to apply a second coat of sealer or finish. This will help to create an even stronger barrier against water damage.

sealing plywood

To apply a second coat of sealer or finish, simply follow the same steps that you used for the first coat. For polyurethane and paint, we recommend at least a minimum of two coats. For epoxy, one coat should be sufficient.

There you have it! Once you’ve applied the second coat of sealer or finish, your plywood will be fully waterproofed and protected from damage.

Waterproofing The Edges of Plywood

Something that we see a lot of people doing wrong is only waterproofing the surface of the plywood. They’ll finish up applying a sealer or a finish and then think that their work is done. And then, later on, they’re surprised to find out that water has seeped into the plywood and completely ruined it.

How do you avoid this? By waterproofing the edges of the plywood as well! And it’s extremely simple to do. When using paint, polyurethane, or epoxy, just remember to add a coat to the edges of the plywood as well. For most people, this is an easy step to forget but it’s an important one nonetheless.

Another way to waterproof plywood edges is to use something called edge banding tape. This is a special type of tape that’s designed to make the plywood more durable and prevent water damage. Make sure you go with PVC edge banding tape as opposed to paper edge banding tape. PVC is much more durable and will better withstand moisture.

Note – To apply edge banding tape, simply peel off the backing and then stick the tape onto the edges of the plywood. Make sure that you smooth out any bubbles or wrinkles as you go! There you have it – fully waterproofed plywood edges ready to take on whatever you throw at it.

5 Methods for Making Plywood Waterproof

We’ve covered a lot of information so far but we haven’t really gone into detail about the different methods that you can use to waterproof plywood. So let’s fix that! Here are five methods that you can use to make your plywood waterproof:

Method #1 – Polyurethane Varnish

This is one of the most popular methods for waterproofing plywood. And for good reason! It’s extremely simple to do and it gives a glossy finish that looks great – especially on outdoor furniture.

Polyurethane varnish comes in both water-based and oil-based varieties. If you’re working with indoor furniture, we recommend using a water-based varnish. But if you’re working with outdoor furniture, an oil-based varnish will be a better choice. This is because it’s more durable and it will better withstand moisture.

polyurethane plywood finish

Method #2 – Epoxy Resin

Epoxy resin is another popular choice for waterproofing plywood. It’s often used on boat floors and other marine applications because it’s extremely durable and can withstand a lot of wear and tear.

One advantage of epoxy resin over varnish is that you can get the same amount of protection for half the number of coats. It’s also a bit more flexible than varnish and can better withstand changes in temperature. So if you’re looking for a long-lasting and durable finish, epoxy resin is the way to go.

Method #3 – Plastic Sheeting

If you’re looking for a temporary solution or something that’s easy to remove, plastic sheeting is the way to go. It’s not as durable as varnish or epoxy resin but it’s much easier to apply and remove.

To use this method, simply cut the plastic sheeting to size and then attach it to the plywood using double-sided tape. Once it’s in place, use a heat gun to shrink the plastic and create a tight seal.

You can use any type of plastic sheeting as long as it’s durable enough to withstand wear and tear, along with water seepage. We recommend using something like PVC or polyethylene.

Method #4 – Liquid Latex

What if we were to tell you that you could simply spray on a waterproofing solution and be done with it? That’s what liquid latex is – a spray-on waterproofing solution that dries to form a durable, rubbery coating.

You can find liquid latex in most hardware stores, and it’s not a very complicated method to use. Simply apply the latex evenly over the surface of the plywood and then allow it to dry. After an hour or so, you can add one more coat for extra protection. And that’s it! Once the latex has dried, your plywood will be fully waterproofed.

Note – Sometimes it can be difficult to gauge whether you’ve applied enough liquid latex. If in doubt, always err on the side of more rather than less. It’s better to have a little more latex than not enough!

Method #5 – Water-Based Paint

Perhaps the easiest method on this list, water-based paint can be applied just like any other type of paint. The only difference is that you’ll need to use a primer beforehand so that the paint will adhere properly to the plywood.

Once the primer is dry, apply a coat or two of paint to the plywood and then allow it to dry completely. That’s it! You now have a waterproof layer of protection on your plywood.

The major disadvantage to this method is that paint is susceptible to chipping and peeling over time. And to counteract this, you’ll need to repaint the plywood every few years but hey, think of all the great colors you can choose from!

What Types of Plywood Are Waterproof?

We’re sure that this is something a lot of you are thinking about right now. Why go through the hassle of waterproofing plywood when you can just buy waterproof plywood in the first place?

The answer is simple – because there really isn’t any 100% waterproof plywood. However, don’t be disheartened. There’s one particular type of plywood that comes pretty darn close – marine grade plywood.

Marine grade plywood is made with waterproof glue, and it’s designed to withstand constant exposure to moisture. It also has no voids in between the layers, which makes it extremely strong and durable. Marine grade plywood is often used in activities such as boatbuilding, docks, and other outdoor applications where water resistance is of the utmost importance.

The only downside to marine-grade plywood is that it’s more expensive than regular plywood. But considering how long it will last, we think it’s definitely worth the investment.

If you’re interested in learning more about marine-grade plywood, we’ve written an entire article on the subject. Be sure to check it out!

The Most Common Plywood Used for Outdoors

So now that we’ve gone over the different types of waterproofing methods and the different types of plywood, it’s time to answer another important question that most plywood hobbyists have – what is the most common type of plywood used outdoors?

Firstly, let’s understand the two types of plywood that are there – interior plywood and exterior plywood.

  • Interior plywood: As the name says, interior plywood is usually used for indoor purposes. Whether it’s for furniture, cabinets, or wall paneling, you’ll be able to find interior plywood in most homes. This kind of plywood is bonded with a substance called urea-formaldehyde (UF), which is a strong adhesive but does not have a lot of water-resistant capabilities.
  • Exterior plywood: On the other hand, exterior plywood is made to withstand harsh outdoor conditions. It’s bonded with a type of adhesive called phenol-formaldehyde (PF), which is waterproof and weatherproof. Exterior plywood is often used in construction projects, as well as for making outdoor furniture and signs.

Here’s a short table showing the pros and cons of each type.

Interior PlywoodExterior Plywood
Strong and durableNot waterproofHighly water-resistantLow thermal insulation
Looks appealingCan bend or sag after a whileBeautiful and aesthetic to look atLow breathability
LightweightIt may look good but be structurally weakStructurally stableNot fire-resistant
FlexibleShould be protected with laminate or wood veneers.Eco-friendlyRequires a lot of energy to produce
Cheap Very strong and wear resistantExpensive
Available easily and in large sizes 
Plywood Types with Pros and Cons

As you can clearly see, there’s only one winner when it comes to choosing plywood for outdoors – exterior plywood! Not only is it more durable and long-lasting, but it’s also waterproof, which is essential for withstanding the elements.

5 Types of Exterior Plywood Used for Outdoors

Now that we’ve established that exterior plywood is the best choice for outdoors, it’s time to take a look at the different types of exterior plywood that are available. Here are five of the most common ones:

1) CDX

All exterior plywood comes with an X stamp along with another letter grade – such as A, B, C, or D. The X rating simply means that the plywood has been tested and is suitable for exterior use. The higher the letter grade, the better the quality of the plywood.

CDX is probably the most common type of exterior plywood used outdoors. One side of the plywood is rated grade C, while the other side is rated grade D. This means that one side is of slightly better quality than the other, but both sides are still suitable for exterior use.

CDX plywood is often used in construction projects where it will be covered up and won’t be visible. It’s affordable and it does a decent job of resisting moisture, making it ideal for projects such as sheds and decks. However, it’s not as durable as some of the other plywood on this list.

2) Pressure-Treated Plywood

Pressure-treated plywood is regular plywood that has been treated with chemicals to make it resistant to rot, insects, and water damage. This treatment usually involves soaking the plywood in a solution of water and chemicals – such as chromate copper arsenate, ammoniacal copper quat, and copper azole. The wood is then subjected to high pressure, which forces the chemicals deep into the plywood.

Pressure-treated plywood is often used in construction projects where it will be exposed to the elements. It’s more expensive than regular plywood, but it’s worth the investment because it will last much longer. However, keep in mind that this type of plywood has a somewhat oily surface and a greenish hue to it, which may not be ideal for all projects.

3) T1-11

Also called plywood siding, T111 is a type of exterior plywood that’s often used for sheds and other outdoor structures. You can find it in both sanded or rough-sawn forms, and it usually comes in four-foot by eight-foot sheets. One side of the plywood is smooth, while the other side has a textured surface with small grooves running vertically.

T111 plywood is easy to work with and is quite affordable for most people. One of the reasons it is quite popular with homemakers is because it can be stained or painted to match the exact color scheme of the house.

4) Oriented Strand Board (OSB)

Invented by Armin Elmendorf in 1963, oriented strand board is a type of engineered wood that’s made by compressing and bonding together strands of wood. These strands are usually thin slivers of spruce, fir, pine, or other types of softwood.

OSB is often used as an alternative to plywood because it’s cheaper and easier to produce. It’s also constructed with water-proof glue which gives it semi-waterproof properties. The best part? You can find OSBs almost anywhere so it’s very easy to source. However, keep in mind that it’s not as strong or durable as plywood.

OSBs are commonly used for sheathing and roof decking.

5) Marine-Grade Plywood

As we’ve already established, regular plywood is not ideal for use in damp or wet conditions. Marine-grade plywood, on the other hand, is specifically designed for use in high moisture environments. The core of this wood consists of knot-free sheets, which ensures that no water-pockets form inside the wood.

More expensive than all the other types of exterior plywood on this list, marine-grade plywood is mostly used for constructions that will be in constant contact with water – such as boats, docks, and other marine structures.

Next time you’re looking for great plywood to use for your outdoor projects, make sure to give one of these five types a try!

Benefits of Waterproofing Plywood

Waterproofing plywood has a whole host of benefits. Here are just a few of them:

  • Prevents rot and decay: Water is one of the main culprits when it comes to causing rot and decay in wood. By waterproofing your plywood, you can prevent these issues from occurring.
  • Makes the plywood more durable: When plywood is exposed to water, it can start to break down and become weaker over time. Waterproofing the wood will make it more durable and long-lasting.
  • Protects against insect damage: Insects are attracted to damp and wet conditions. By waterproofing your plywood, you can keep these pests away. You’d definitely not want termites or other insects destroying your beautiful plywood project!
  • Enhances the appearance of the wood: Waterproofed plywood has a nice, smooth finish that looks great. Not to mention, it’s also much easier to clean!
  • Increases the lifespan of the wood: Waterproofing plywood can help to increase its lifespan. Replacing plywood every now and then can be a costly endeavor, so it’s definitely worth it to waterproof the wood to make it last longer.

As you can see, there are many benefits to waterproofing plywood. So what are you waiting for? Get started today and enjoy all the benefits that come with it!

Frequently Asked Questions (FAQs)

Here are some of the most commonly asked questions regarding how to waterproof plywood.

Q.1. Is marine plywood waterproof?

A. Marine plywood is a type of plywood that’s specifically designed for use in high moisture environments. It’s made with water-resistant glue and the core of the wood consists of knot-free sheets, which makes it more resistant to water damage.

Q.2. What is the best way to waterproof plywood?

A. There are several ways to waterproof plywood. You can use a waterproofing sealer, paint, or stain. For best results, it’s recommended that you use a combination of two or more of these methods.

Q.3. Can I use regular plywood for outdoor projects?

A. No, regular plywood is not ideal for use in damp or wet conditions. It’s important to use a type of plywood that’s specifically designed for outdoor use. If you’re not able to get your hands on proper, exterior-grade plywood that’s water resistant, you can always waterproof regular plywood to make it more durable and long-lasting.

Final Thoughts

We hope that you now have a better understanding of how to waterproof plywood and the best methods to use. Waterproofing plywood is a great way to protect your investment and make sure that your project lasts for many years to come. Whether you’re a newbie about to work on your first project or you’re a seasoned pro, remember our tips and your plywood creations will look gorgeous forever. Good luck!

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