How to Waterproof Plywood

Plywood is a good, readily available building material, with multiple applications in your interiors and exteriors. However, unlike plastic, it is not waterproof. To protect plywood from water damage, there are many types of waterproofing available. Most are easy DIY projects that will save you time and money. Read on to learn of the effective ways to waterproof plywood to stop the glued layers from disintegrating, rotting and peeling apart from excessive water exposure.

What Happens When Plywood Is Exposed to Moisture?

Plywood is made up of thin layers of laminated softwood, held together by strong, adhesive glue. When exposed to moisture, the wooden layers can swell or deform. As for the glue bond, it weakens when the wood stays wet for a prolonged period, and the layers can separate eventually. Besides delaminating, plywood exposed to moisture also grows molds.

There are several measures you can take to avoid exposing your plywood to moisture to avoid damage.

  • During the construction process, make sure you cover your plywood and keep it elevated from the ground.
  • Prior to installation, use a paintbrush to apply a weatherproof stain or water-repellent preservative.
  • For the protection and a more aesthetic appearance, apply an outdoor, latex-based paint to your plywood.
  • Apply varnish on the plywood edges to seal and protect from water that may seep through.

What Can I Use to Waterproof Plywood?

There are many types of waterproofing options to protect plywood. In most home improvement stores, however, the most commonly sold type is the spray-on or paint-on type of waterproofing. These are usually liquid latex substances applied to the plywood surface while wet. They then form a plastic, protective layer once they’ve dried. Other types of waterproofing include;

In most cases, waterproofing membranes and paint-on are used where plywood is under natural stone or tile installations. Spray-on sealers and preservatives are used on finished plywood to retain the wood look.

The application of most of the liquid waterproofing substances can be done using a brush, roller or sprayer. Plastic sheeting will typically need to be stapled or tacked up, and so do overlapping and interlocking membranes.

The first step to protecting your plywood is to determine whether you’re dealing with an exterior or interior setting since each has its own concerns. While you would need a full protective coat of waterproofing for plywood for an outdoor siding application, for areas where water and moisture issues will be minimal, penetrating oil with an antifungal preservative can be sufficient.

How Do You Seal Plywood from Water?

The best way to seal plywood outdoors is to apply an epoxy seal to the plywood’s surface to condition the wood and prevent water from penetrating. You should easily buy an epoxy sealer for plywood from your local hardware store.

For this, you will need:

  • A good water sealer
  • Exterior polyurethane varnish
  • Small stain brush
  • Pigment stain(water-based)
  • Pump-up garden sprayer

To waterproof exterior playground;

  • Use the stain brush to apply several coats of the exterior polyurethane varnish to the edges of your plywood to seal them. But, keep the varnish away from the surface of the plywood, by taping with masking tape.
  • Then, use a garden sprayer to coat the plywood surface with an exterior water-based pigment stain to tint it and protect against UV damage.
  • Let the plywood dry for 24 hours.
  • Once dried, apply a water sealer to the plywood’s surface using a pump-up garden sprayer.
  • Apply several coats of the sealer, and re-apply after every two years.

It’s worth noting that the epoxy seal coat will not stick to an oil-based stain or oil-based paint.

Sealing Plywood with PVA

PVA (polyvinyl alcohol, polyvinyl acetate) is a synthetic polymer that is soluble in water. It’s effective in film-forming, emulsifying and is adhesive. It can also be effective for sealing your plywood to give it a waterproof quality. However, it is not the best product to use if your plywood surface is external and likely to be washed with rain regularly.

For this process, you may need to apply at least 3 coats of undiluted PVA, making sure each coat dries up thoroughly before applying the next.

Waterproofing plywood can help prolong its life and keep it in good condition. There are different ways to do it, but first, you need to determine whether it’s for indoors or outdoors application. It’s also important to follow the recommendations of your finish product’s manufacturer when installing a protective layer for your plywood.