How To Waterproof Plywood? (3 Simple DIY Steps For Everyone)

Although plywood is an excellent building material, not all sheets are created equal. You’ll need to discover how to waterproof plywood if you have ordinary plywood sheets that have been exposed to water. 

This process will save you money in the long run by preventing costly repairs. To make plywood waterproof, you have to go through these stages:

  • Prepare plywood
  • Apply the paint/sealer
  • Let it dry

Let’s dive into this article to grasp the details.

First Of All, Is Plywood Waterproof?

Water-resistant, which is not waterproof, is the best way to describe plywood. But, even then, the label “water-resistant” could be a stretch! Small quantities of water will not harm it, but continuous moisture absorption can be fatal. 

Plywood Is Made Of Thin Veneers

Plywood is made up of thin veneers that have been laminated and bonded with pressure and heat. Although it is a tricky substance, moisture can penetrate the layers, causing them to split or fracture. 

When manufacturing wood, the plywood is soaked with water, which absorbs into the wood and causes it to expand. Then it is squeezed out as the surfaces are heated, causing the wood surfaces to bind even tighter. 

As a result, plywood and water aren’t incompatible. Water makes plywood susceptible to damage because it causes each layer to expand again. Because the adhesive that keeps the layers connected can’t resist the gradual expansion, the wood layers will split over time, ripping away. 

Depending on how much water the wood is exposed to, this might take several years or months. When exposed to moisture, plywood behaves differently than solid one. 

If a wood beam is wet, it absorbs water and gradually degrades, but it will not lose its structural integrity readily. However, the consequences of water damage on the wood are significantly more important since water fractures the layers.

Types Of Wood Waterproofing

There Are Many Waterproof Products To Treat Plywood

Waterproofing products and procedures appear to protect plywood in various ways, and you definitely want to make sure you’re using the one that is best for your plywood’s use. 

Paint-on or spray-on waterproofing is the most common form of waterproofing you’ll encounter. This type of waterproofing is typically a liquid latex that you apply on damp plywood. 

As it dries, it forms a protective barrier against moisture. This substance can be found at almost any hardware shop and is simple to install on your own. It’s as simple as putting it on and waiting for it to dry completely. 

Water-resistant sealers, waterproofing solutions, and sheet polymers are all available to prevent moisture damage. Remember to choose the method and procedure that is most appropriate for your project.

How To Waterproof Plywood (Detailed Instructions)

We have gone through the various waterproofing options for plywood; it’s time to get to seal it.

Step 1: Prepare your plywood

It’s necessary to prepare the board before applying liquid latex, PVA, or paint. First, remove any filthy areas from the plywood’s surface using a dry cloth or a brush. 

Then, using wood filler, smooth down any rough places on the sheet’s surface. This way gives it a consistent smoothness and avoids any waterproofing cracks. Allow the filler to dry and solidify before moving on to the next stage. 

Wipe Down The Wood Sheet With Towel

Wipe down the wood sheet with a damp towel after the wood filler has dried. The tiny quantity of moisture helps the sealer adhere to the plywood sheet by raising its grain.

Sand the plywood lightly with moderate (roughly 60-100 grit) sandpaper as the final stage in preparation. It helps smooth the wood sheet and eliminate any rough areas that may cause the sealing to “gunk up.”

Step 2: Apply the paint/sealer

Apply The Water-Resistant Substance Onto The Wood

If you use a brushed-on finishing technique, apply it with a roller or brush as usual. Notice that you obtain a good covering with the first layer and wait for it to dry before adding the second. Some waterproofing requirements may necessitate the third layer. While this isn’t strictly essential, it can’t hurt. 

Read the company’s directions carefully if you are utilizing a spray technique. When spray-on sealer is misused, one of these things happens:

  • Not enough sealer to fully cover the surface.
  • Having inconsistent concentration, with a lot of sealer in some spots and none in others.

These dangers occur because spray-on sealers are more challenging to see and manage than brushed-on ones. So, while you’re spraying the sealer, think about where you’re aiming.

Step 3: Let it dry with care

Allow at least a couple of hours for the plywood board to dry, and up to one day if you have time. Once it is scorched, put it in place and apply a little sealant over the nails once the plywood is fitted to keep it waterproof.  

Finally, even if your wood sheets are waterproof already, you should inspect them every several months to ensure that water is not causing havoc behind your back. 

Flood damage will be apparent, so it shouldn’t seem like a complete examination to ensure everything is in working order. You can rely on the instructions in this video to better understand how to waterproof plywood.

Bonus Tips: How To Seal The Edges Of Your Plywood Board?

We have covered how to protect a plywood surface, but how about the edges? Is it necessary to waterproof them, and if so, how to do so? The margins of wood are susceptible to water since it is made up of multiple layers. 

Plywood Edges

When water comes into contact with the plywood edges, it splits considerably more quickly than it would on the surface. As a result, waterproofing the margins is critical—perhaps even more so than waterproofing the surfaces. 

Apply multiple coats of varnishes to the plywood edges, giving each layer to cure for roughly an hour between applications. Because the edges quickly absorb the varnish, you’ll need additional coats to ensure that it cures to produce that protective coating.

Why Should You Waterproof Plywood?

If plywood boards have been put inside houses for decoration or personal preference, they must be waterproofed. Waterproofing plywood makes it waterproof, insect-proof, inhibits wood swelling, and avoids mold growth by keeping water from penetrating the wood. 

If your wood becomes wet, it might break due to frost throughout the winter. Exterior timbers that are well-protected will age more slowly and keep their natural look. 

Sealing is almost as critical for plywood used indoors as it is for plywood used outside. It would be best to soaked barriers, floor coverings, and windows made of plywood more frequently to provide continual wood protection. 

As a result, if we have chosen to install wood or plywood panels, particularly near balconies or windows, it is critical to operating with precision in waterproofing. In addition, condensation is formed because of the usage of air conditioners, which contributes to staining them. 

Frequently Asked Questions

Here are some related questions we have collected while researching this field, which may benefit you.

1. Is treated plywood waterproof?

While we still have plywood pressure-treated, it seems more of a surface-level treatment since the solution only penetrates the plywood’s exterior layers and borders. 

As a consequence, even pressure-treated plywood must be well waterproofed and sealed on both sides.

2. How long does untreated wood last outdoors?

Water Damaged Plywood

If you put an unsealed plywood sheet on an outside building, it would endure for around two years. The plywood would begin to decay within the following year, caused by exposure to rain, wind, and sunshine. Finally, after two years, it would have collapsed.

3. Is it possible to use Flex Seal on plywood?

First and foremost, Flex Seal is a convenient technique to seal practically everything. You can quickly apply liquid latex onto the wood with this aerosol sealer. 

When compared to spraying sealer with a brush, it can save you a great deal of time. It is also convenient since it makes applying an application to the whole plywood sheet a breeze. 

Furthermore, the latex spray particles can readily penetrate the wood pores. Plywood is not a big deal for Flex Seal because it can seal almost any surface layer, including pipe, plastic, and even ceramic. 

After all, Flex Seal isn’t the finest sealant on the market. Although it is resistant to water, it is not waterproof. In addition, the exposure of a plywood sheet to the elements such as rain and humidity is a significant reason to be concerned.

To get right to the point, do not apply Flex Seal on your piece of wood. There are far better wood sealers available.

Final Thoughts 

Knowing some plywood waterproofing and sealing techniques is critical if you want your house or shed to last longer. Honestly, it is pretty straightforward, and everyone can make a sheet of plywood waterproof with some steps and a little care.

Furthermore, because some varieties of plywood are water-resistant, you may never have to waterproof it if you pick the plywood carefully. We hope this article benefits you in learning how to waterproof plywood correctly.

Thanks for reading!