Sealing Plywood Edges For Exterior Use: 5 Effective Methods

As a type of pressure-treated wood, plywood is quite susceptible to damages when used as an exterior material. It will degrade when continuously exposed to moisture, dirt, dust, and changing weather. The plywood edges are the common entry points of these elements since it exposes the core material. With this, sealing plywood edges for exterior use is advisable.

In this post, I will share five methods you can try to seal the edges of your plywood. Each of these offers varying levels of protection against moisture. Check which of these suits your project best.

Why do you need to seal the edges of the plywood for exterior use?

Sealing plywood before use is crucial to increase its longevity. Here are some of the reasons why you should never skip sealing the edges of your plywood:

  • Preventing rot. Pressure-treated wood like plywood is prone to rot if not sealed or treated. Once moisture enters the core, it will start to harbor mildew, which will start the wood rot. This will not happen if you seal the edges first.
  • Preventing splitting. Plywood used as exterior material without sealing will split easily. The glue between veneers will lose its tackiness. Soon enough, the plywood will warp and disintegrate.
  • Avoiding moisture penetration. Moisture and sunlight are the two biggest enemies when using plywood as an exterior material. Sealing the edges will prevent twisting, expansion, and shrinking of the material.

Methods to seal plywood edges for exterior use

There are three common methods in sealing the edge of the plywood. Below, I discussed the steps for each one:

Method 1. Using a water-based finish

When sealing the edges of the plywood, a water-based stain is a good option. This may sound counter-effective, but hear me out.

When applied to plywood edges, water-based stains will prevent the growth of mildew. It will also allow air to get in and out of the plywood core, which will prevent moisture retention.

You can choose between water-based stains or water-based paint. However, you should note that paints require frequent touch-ups.

Nevertheless, here’s how you should apply it:

  • Using a pump sprayer, apply the stain along the edge of the plywood.
  • Let it dry based on the recommended period on the container.
  • After a few minutes, wipe off the excess stain/paint that drips from the plywood.
  • Leave the plywood to dry for 24 hours before use.
  • Feel free to apply multiple coats for the best protection for your plywood.

Method 2. Using polyurethane varnish

If you’re not a fan of stains, polyurethane varnish is your best bet. This coating is super tough and will serve as a protective layer at the edge of the plywood material. It’s often used on wood that will be installed on high-wear areas like stairs, exterior floors, and so on.

Aside from that, water-based polyurethane varnishes have lower VOCs than solvent-based types. If applied properly, polyurethane varnish can be as tough as a liquid plastic coating. Here’s how to do it:

  • Cover the adjacent areas of the plywood edge to prevent the varnish from getting into the surface. You can use painter’s tape.
  • Using a brush, apply a coating of polyurethane varnish at the edge of the plywood.
  • Let the first varnish coating dry for 30 minutes.
  • Next, apply another coating, then let it dry again before putting more layers.

Method 3. Using a water sealant

If you’re placing the plywood on high-moisture areas, it’s crucial to use a water sealant. This will block the entry of water into the plywood so that it won’t warp or rot. In most cases, woodworkers apply the sealant throughout the plywood to make it waterproof.

When applied to wood, the marine or water sealant will block the wood pores. It will make water penetration impossible. This is why woodworkers use water sealants when installing plywood on boats and other vessels.

Here are the steps you need to take to seal the plywood edges:

  • Using a pump sprayer, apply the water sealant on the edges of the plywood
  • You can smooth out the first coating using a spare piece of wood.
  • Let this dry based on the instructions on the sealant container.
  • After that, you can apply more coatings to boost the waterproofing of the plywood edges.
  • It’s advisable to re-apply the sealant to the plywood edges every two years.

Method 4. Using liquid latex

If you don’t have the time to spare, liquid latex is an excellent alternative. It’s also a good choice if you’re only working on a few pieces of plywood. But if you’re dealing with a large project, liquid latex will be expensive and impractical.

Nevertheless, liquid latex bonds well to the edge of the plywood. Just make sure that you apply it lavishly, as it can be tricky to know if you already applied enough.

If properly applied, liquid latex can seal the edges of the plywood for years. Here’s how to do it:

  • Using a rag, wipe the edges of the plywood to remove dust and dirt.
  • You can use a paintbrush to apply the liquid latex or a spray can.
  • If you prefer rolling or brushing, make sure that all spots of the plywood edge are covered.
  • After that, let the latex dry for an hour. Latex dries quickly than stains.
  • Feel free to add another coat if you want to seal the plywood edge further.

Method 5. Using epoxy sealer

Lastly, you can use an epoxy sealer. This is more durable than latex and can protect the plywood from chemicals, moisture, and other outdoor elements.

You can get epoxy sealers in spray forms for a more convenient way of application. It will harden and make the plywood edges waterproof. Here’s how to apply it:

  • Using a paint roller, saturate the edges of the plywood with epoxy.
  • Make sure that all the edges are covered.
  • After that, let the epoxy sealer dry for 10 to 12 hours before using the plywood.
  • You can also apply another coating for better sealing.
  • Can you make plywood waterproof?

It’s possible to make plywood waterproof. You simply have to coat the entire material with a waterproof seal. A marine sealant, epoxy, latex, and similar finishes can prevent water from penetrating the wood grains of plywood.

Just make sure that you let the coating dry before use. You should also consider applying multiple coats, especially if you’re using plywood on a high-moisture area.

Remember that, as with any pressure-treated wood, plywood isn’t invincible to damage. Even if you seal it well, plywood will reach its end of life as an exterior material after a few years.

How long will untreated plywood last outside?

Untreated and unsealed plywood will deteriorate fast outdoors. If you place it in an area with high moisture and extreme temperatures, plywood will warp and rot in a matter of weeks.

In general, untreated wood will last for up to two years outdoors. But in the case of plywood, you’re lucky to stretch it to a few months outdoors without any treatment.

How can you make untreated wood last outside?

You can only do so much to make untreated plywood last outdoors. Your best bet is placing it on an elevated surface away from moisture and direct sunlight. Still, you can only stretch the wood’s lifespan to a couple of months, especially if it’s pressure-treated.

If you’re keen to make plywood last long outdoors, you should at least seal its edges. That way, moisture won’t get into the core and cause rot.

Does Flex Seal work on plywood material?

Flex Seal is a type of rubber sealant used on a variety of wood projects. It adheres well to almost any surface, including the edges of the plywood.

If you’re looking for a quick fix, Flex Seal is a good option. It’s available in aerosol cans for hassle-free application.

However, it’s not the best sealer in the market. Flex Seal isn’t watertight, which means it only provides minimal protection for plywood.

You can use multiple coatings for better sealing, but rubber sealants don’t usually fill plywood voids. Plywood voids are the gaps in the core material. After all, plywood is made of pressed wood chips and not of solid material.

Do plywood edges paint well?

Plywood edges paint well, but you have to sand and smoothen it first. Otherwise, the rough surface won’t take paint properly.

After sanding, you should apply a wood filler to seal plywood voids. Once it dries, you can now apply your choice of paint. You’ll notice a smoother paint finish as the wood filler has leveled the plywood edges well.

Take note that the wood filler doesn’t have to look good. Don’t worry if it doesn’t look polished. Once you apply paint to it, the edges should look smooth.

Conclusion

Sealing plywood edges for exterior use will extend the lifespan of the material. It will prevent rot, warping, and damages. Nevertheless, make sure that you invest in high-quality plywood for the methods above to work well. And as with any sealing technique, trying it on a spare wood piece is always advisable.

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