How to Waterproof Plywood Including Its Edges

How to Waterproof Plywood Including Its Edges

Handyman's World is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to amazon.com.

Plywood is a great building material, but it does often have problems resisting the effects of moisture. Luckily, it is very easy to waterproof this, and it can be done in various ways.

Right now, we want to talk about five different methods for waterproofing and sealing your plywood.

Is Plywood Waterproof or Does It Need Sealing?

Many types of plywood are water-resistant, but that’s not the same as being waterproof. When it comes down to it, most types of plywood, if not all of them, are not 100% waterproof. Now, some types, like marine plywood and exterior plywood (designed for exterior use), are highly water-resistant, but still not waterproof.

No matter the type of plywood, if it is going to be exposed to moisture and sunlight on a regular basis, you do really want to seal it before building with it.

How to Waterproof Plywood: Five Methods

There are a few different ways to waterproof plywood, including its edges. In this article, we will look at the five most common ones.

Method #1: Using Polyurethane Varnish

Polyurethane varnish is not very expensive, it allows the plywood to retain its natural color, and it will help prevent water penetration.

Now, something to note with this method is that this varnish is best used for the edges of the plywood, but not for the actual surface. The reason for this is because if you treat the surface of the plywood with polyurethane varnish, the plywood will no longer be able to accept future treatments. You may do this, as long as you are aware that you won’t be able to apply any other substance to the surface of your plywood after the varnish.

Step 1: Gather Your Materials

For this method, you will need the polyurethane varnish of choice, some masking or painter’s tape, and a paintbrush.

Step 2: Tape off the Plywood

As mentioned earlier, this method is best used for sealing the edges, but not for the surface of the plywood. If you do only need to seal the edges, use masking or painter’s tape to tape off the surface of the plywood, to avoid getting varnish on it. That said, if you are sure that you won’t be applying more coats to the plywood in the future, then you may apply the varnish to the surface as well.

Step 3: Apply and Repeat

Now, just use the paintbrush to apply the varnish to the plywood. Wait about 30 minutes for it to dry, and then apply a second coat. You may want to repeat this and add a third layer for the best results.

Method 2: Using Water Seal

You can find dozens of different types of water seal or wood sealer for waterproofing purposes, even ones that are specially designed for plywood. You can find ones with color and ones without, so you get the exact look that you want.

Water Seal for Plywood

Step 1: Gather Your Materials

All you will need for this task is the water seal product of your choice, as well as a pump-up or garden sprayer for easy application.

Step 2: Seal the Surface

Fill your garden sprayer or pump-up sprayer with the water sealant. Lean the plywood against a flat surface (preferably one you don’t mind getting some sealant on) and spray the water seal onto the surface. Let it dry for as long as the product instructions indicate, and then apply a second layer for the best results. Repeat this for the other side.

Step 3: Seal the Edges

Use something like a worktable or sawhorse to lay the plywood down flat, elevated in the air. Now, simply use your pump-up sprayer to apply the water sealant to the four edges of the plywood. Once again, for the best results, a second layer is recommended.

Method 3: Using an Epoxy Sealant

Epoxy sealant is a very popular choice to consider, one that works well for plywood surfaces and edges. It allows the wood to retain its natural color while also providing a hard, durable, and protective layer that will guard against moisture, UV rays, and more.

Smith's Original Clear Penetrating Epoxy Sealer [CPES] 2 Quart - Warm Weather Formula (WW)

Step 1: Gather Your Materials

For this method, you will need a two-part epoxy sealant, some kind of disposable cup or container, and a good paintbrush.

Step 2: Sand it Down

Use a bit of sandpaper to sand down the surfaces of the plywood, as well as the edges. You don’t want any splinters present when you apply the epoxy sealant.

Step 3: Mix the Epoxy Sealant

Epoxies always have two components, the resin and the hardener. These need to be mixed together as per the directions on your specific product. Use your disposable cup or container for this. Just remember that this stuff dries and hardens within minutes, so working quickly is of paramount importance.

Step 4: Seal the Surface

Lay the plywood flat on a table or work surface, and use the paintbrush to quickly and evenly apply a layer of the sealant. It only needs one layer, and it needs only a few minutes to dry. Once dry, repeat this on the other surface.

Step 5: Seal the Edges

Once both surfaces are sealed, you can work your way around the edges with the paintbrush and the epoxy sealant. If possible, smooth the edges out before the epoxy dries.

Method 4: Spray-on Latex and Paint

When it comes to waterproofing plywood, this may actually be the best method at your disposal, a combination of spray-on latex and paint. Painting is one of the most common ways to seal plywood and other types of wood. This method is great for plywood that will be directly exposed to the elements.

Step 1: Gather Your Materials

For this method, you will need the paint of your choice (it should be waterproof!), a can of spray-on latex sealant, and some sandpaper.

Step 2: Sand the Plywood

You now want to sand the plywood down using some basic sandpaper, just so that it is smooth and has no rough edges or splinters sticking out.

Step 3: Apply the Spray-on Latex

With the plywood resting on a surface, spray one side of the plywood with the latex. Allow it to dry according to the instructions, flip the plywood over, and treat the other side. Once this is done, you can then spray the edges of your plywood. Now, this may be enough if the plywood is not going to be exposed to moisture constantly, but if it is, you will want to do the next step as well.

Step 4: Apply the Paint

Once all surfaces and edges of the plywood have a layer of spray-on latex that is totally dry, you can then go about applying a layer of waterproof paint to all surfaces and edges.

Method 5: Using Penetrating Hard Oil

Penetrating hard oil is a special type of oil that has the ability to penetrate the exterior surface of wood, soak into it, and provide a moisture barrier. This method is ideal for plywood that will be exposed to small amounts of moisture, but the oil may dry out over time, so if exposed to the elements on a regular basis, coats of oil will need to be regularly applied.

Step 1: Gather Your Materials

Get the penetrating hard oil of choice, a paintbrush, and a paintbrush.

Step 2: Sand the Plywood

You need to sand the plywood down so that there are no rough edges or splinters protruding.

Step 3: Seal the Surface

Using a paintbrush, simply apply a small amount of the oil onto one surface of the plywood, let it dry, then do the other side. For the best results, you want both surfaces to have two layers of oil.

Step 4: Seal the Edges

Evenly apply the penetrating hard oil to the edges of the plywood, let it dry, and then apply a second coat.

Mistakes to Avoid, Tips & Tricks

Let’s go over some quick tips and tricks for you to follow so you can achieve the best results when waterproofing plywood:

  • Whenever working with any of these substances, especially if you have sensitive skin, wear protective gloves.
  • Some of these sealants release noxious fumes, so it is always best to work in a well-ventilated area.
  • Always let coats dry totally before attempting to apply a second coat. Applying coats of these products onto underlying coats that are still wet will not go well.
  • Always do this on a day with nice weather and a moderate temperature, as this will allow for the best results as your sealants dry.

Summary

As you can see, there are many methods at your disposal for waterproofing plywood. Some are best used for when plywood will be exposed to minimal moisture and some are best for maximum protection, while some are best for plywood surfaces and others for the edges.

Choose wisely!