How To Waterproof Plywood

Plywood is made from thin sheets of wood glued together and is the most frequently bought form of lumber in the world. While it’s strong and can even be pliable, it’s not waterproof. In fact, even though it floats, wood is in no way waterproof. 

All trees absorb water, even after they’ve died or have been cut down and milled. The only difference is that the dead or milled wood doesn’t use the moisture, so it just sits, slowly destroying the wood from the inside.

So, unless you want to spend your life replacing waterlogged and crumbling plywood, keep reading to learn how to waterproof plywood for both indoor and outdoor use.

How To Waterproof Plywood

What Water Damage Does To Plywood

Again, plywood is very susceptible to water damage.  Wood is very absorbent and will soak up moisture which can cause a wide variety of issues that include:

  • Water stains and swelling. If the plywood is painted, the paint will peel, bubble, and chip off.
  • Wood rot will eventually crumble the plywood.
  • Splitting, and warping the wood.
  • Promoting Mold and Mildew growing in the cracks and crevices.
  • Attracting bugs like termites and carpenter ants.

You can prevent all of these issues and preserve your plywood for much longer by using a waterproofing agent to seal it off from water and other damaging weather elements.

How To Waterproof Plywood

Different Types of Plywood

There are also different types of plywood, some more water-resistant than others. If you want something that’s going to be able to hold its quality against a lifetime of water, you will have to look for a higher quality type of plywood.

For example, pressure-treated wood is the most common type of plywood used for indoor purposes because it’s relatively cheaper and can be used throughout a whole home. However, marine-grade or urethane-coated CDX plywood is much more water-resistant for outdoor use or sub-flooring because it is already treated to withstand water.

Also, if you’re going to be waterproofing a larger area of plywood or a whole house, you may want to think about enlisting professional waterproof experts to help you fortify your house to prevent flooding and water damage. Otherwise, waterproofing is pretty simple to do on your own.

The Best Products To Waterproof Plywood

There are several ways you can waterproof plywood. However, some solutions will work better in different environments. For instance, indoor and outdoor plywood will require different types of waterproofing solutions. Usually, exterior plywood will need a heavier waterproofing agent to be able to stand up to rain, snow, ice, and humidity.

Latex-Based Paints

One of the most popular ways to waterproof plywood is to simply paint it. Latex-based paints like Rustoleum Painter’s Touch and Valspar’s Porch and Floor Enamel are waterproof and can protect plywood from all kinds of conditions. And this way, the plywood can be whatever color you want it to be.

For the best effect, latex paint is applied on dry wood. The water and latex form a protective barrier that keeps water, fungus, and bugs out of plywood.

To apply:

  • Sand the plywood to create a smooth surface.
  • Clean and slightly dampen wood with a wet cloth.
  • With a brush, paint the whole surface of the plywood.
  • Let dry for a couple of hours.
  • Paint a second coat.
  • Let dry up to 24 hours for the best protection.
  • Repaint every year, if needed.
Valspar 27-1500 QT 1 Quart White Porch and Floor Latex Satin Enamel

Valspar 27-1500 QT 1 Quart White Porch and Floor Latex Satin Enamel

  • 27-1500 QT 1 Quart White Porch and Floor Latex Satin Enamel
  • Used For Painting Supplies, Paint & Stains Accessories
  • Product is manufactured in United States

Such a vibrant, beautiful color! Perfect for the money and I’m so thankful I found this to paint.

Epoxy Water Seal

Another popular option, epoxy seals like Max Bond are extremely effective, retain the original wood coloring, and will last much longer than other types of waterproofing agents. But, epoxy will harden much quicker than the other types of waterproofing solution, so you will need to be time-focused in order to have a smooth barrier. 

When the 2 parts of an epoxy kit are combined, they form a plastic-like barrier around the wood. This makes it the perfect choice for plywood that is going to be exposed outdoors. With epoxy seals, your plywood is fiercely protected from more than just water. It’s also protected from the heat, the cold, fungus, and so much more. 

To apply:

  • Sand and wipe down the plywood to clean it.
  • Apply an even coating of the epoxy without rushing. Read directions and follow closely.
  • Let it dry according to the product’s instructions.
MAX Bond Low Viscosity Marine Grade Epoxy Resin- 1 Gallon Kit

MAX Bond Low Viscosity Marine Grade Epoxy Resin- 1 Gallon Kit

  • Marine Grade Structural Fiberglassing Impregnating Resin
  • High Impact Resistant, Excellent Durability
  • Low Shrinkage, Wide Range Of Service Temperature

Used product on projects that needed to be 100% waterproof, so far so good. Easy to use.

Penetrating Oil Treatments

Penetrating oil treatments like Thompson’s Water Seal is an oil-based waterproof sealer that works perfectly for indoor use. It even has antifungal properties, so you get a double dose of protection from mold, mildew, and other fungi.

As you can see from the name, the oil soaks into the plywood’s surface. Once it dries, it will repel all types of moisture from dew to snow and ice. 

Here’s how to properly apply it:

  • Thoroughly sand the plyboard surface and clean off all debris.
  • Using a pump-up garden sprayer or a large paintbrush, saturate the entire surface of the plywood.
  • Wipe off any drips coming from the edges.
  • Let it dry, according to the manufacturer’s instructions.
  • If needed, apply a second coat and dry again.
  • For the best finish, let it sit for 24 hours before touching it.
CHAPIN 20000 Garden Sprayer 1 Gallon Lawn

CHAPIN 20000 Garden Sprayer 1 Gallon Lawn

  • 1-Gallon funnel-top, translucent tank for easy filling and cleaning
  • Ergonomic handle for easy pumping and carrying
  • Spray/Flow Rate (GPM) : 0.4 - 0.5 gpm adjustable

It’s a squirty and spraying pump pressure pot squirt gun! works really well. and made well.

Sealing Varnish

Using a polyurethane varnish, like Miniwax, is one of the most common ways to seal plywood. While there’s more odor than any of the other methods, a polyurethane varnish will last years and resists sun, frost, and heat as well.

To apply:

  • Thoroughly sand and clean plywood.
  • Lay down first coat and let dry completely.
  • Repeat for the second and third coats for maximum protection.
  • Leave to set and harden for up to three days.
Minwax 63005444 Fast Drying Polyurethane Clear Finish

Minwax 63005444 Fast Drying Polyurethane Clear Finish

  • Provides long-lasting beauty and protection to any interior wood surface
  • Ideal for woodworking, furniture, doors, cabinets and floors
  • Can be used on both finished and Unfinished wood

Good product, very quick drying time.

Liquid Membrane

If the plywood you’re waterproofing is going to be seeing constant water, one of the most fail-proof ways to do it is to thickly coat it in a liquid membrane like Liquid Rubber.

This turns the surface into a silicone-like product that is flexible enough to move with frost and shift over time but is strong enough to repel water and sun damage for up to 10 years. To apply, simply put on one even coat and let it dry for 48 hours.

Liquid Rubber Color Waterproof Sealant

Liquid Rubber Color Waterproof Sealant

  • Highly Flexible & Durable
  • Environmentally Friendly
  • For a Bulletproof System

It’s an amazing product!!! This seals great & fast and easy water clean up.