How to Waterproof Plywood (4 Effective Methods)

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The true value of plywood is far from a mystery. Due to its composite cross-grained design, plywood tends to be quite strong at any given thickness, and far more impervious to shrinking/expansion than standard boards. Plywood also resists cracking and splitting when being nailed or screwed in place around its perimeter edges.

However, not all plywood is waterproof, and which tends to be relatively pricey. Luckily, those with the drive, and a dose of ingenuity, can waterproof their plywood, saving money along the way. In fact, there is more than one way to handle such tasks, each of which offers its own distinct benefits.

The process of waterproofing plywood is not only far simpler than most would imagine, but is also great for extending the longevity of such materials. As such, one can expect the fruits of their labors to stand the test of time, come rain or shine.

Read on to learn more about the benefits of waterproofing plywood, as well as the details you need to complete such a project yourself.

See Also: Best Concrete Sealers For Your Garage

Benefits of Sealing/Waterproofing

how to waterproof plywood

There are numerous benefits to sealing/waterproofing your own plywood, the majority of which should be appreciated by the bulk of DIY enthusiasts. The following are several of the most notable benefits associated with such efforts.

Prevents Swelling

Wood of any type naturally absorbs water, with composite materials such as plywood being no exception. This water absorption causes wood to swell, which can be quite problematic when already fastened in place as an integral piece of any project. 

When wood swells, it often distorts. This distortion impacts the alignment of pieces of other pieces of wood that are fastened to a swollen board. In short order, what was once square, will be far from true at most every joint and junction.

Waterproof plywood resists water absorption, thereby minimizing the chances of swelling. This enhances the longevity of any structure or project, and lessens the chance of unsightly cracks and splits over time. When used for flooring or as a garage ceiling alternative, plywood that swells is a big problem.

Prevents Mold

water damaged plywood

Where there is water, there will also be mold. Water-logged wood is no exception to this rule and serves as a regular breeding ground for mold. Perhaps the biggest problem with mold, is that it is difficult to stop once it has begun.

Mold, if left untreated, can cause additional decay over the course of several years. This decay can drastically reduce the lifespan of any structure, and can also be hazardous to one’s health, if found in confined spaces.

Waterproof plywood sheds water, rather than absorbing it, thereby resisting mold growth. In every case, preventing mold is much easier than stopping its progress in hindsight.

Prevents UV Damage

With time, plywood used in an exterior setting can succumb to the effects of prolonged UV exposure. Just as your skin sunburns under direct sunlight, the sun’s UV rays can cause wood to become overly dry and brittle.

After years of being left untreated, wood often begins to split along its grain, in a largely uncontrolled manner. Once this process begins, rapid deterioration is inescapable. Combined with the effects of intermittent waterlogging, untreated plywood stands little chance of holding up to nature’s wrath.

Aside from its obvious water-proofing related benefits, sealing plywood also reduces weathering associated with direct UV exposure. This serves as a double edged sword in the fight against premature deterioration.

How to Make Plywood Waterproof

Method #1 – Epoxy Resin (Best Way)

seal plywood with epoxy resin

One of the best possible ways to waterproof plywood is through the application of epoxy resin, such as TotalBoat Clear Penetrating Epoxy or Smith’s Original Clear Penetrating Epoxy. This hearty sealant not only provides a respectable-looking finish but is largely impervious to the effects of moisture on an ongoing basis.

Prior to applying epoxy resin, all surfaces that are to be treated should be thoroughly sanded to eliminate gouges and rough spots. It is also advisable to use a tack cloth to remove as much dust and excess particles from the sanding process, before beginning the application process.

Epoxy resin, as well as its hardening agent, should be poured into a clean container and stirred thoroughly. This mixture can then be evenly applied with a bristle brush. Be sure to allow 24 hours for your newly applied epoxy to fully cure.

Method #2 – PVA Glue

PVA glue to seal plywood

Though PVA glue is often thought of as an end sealer for waterproofing plywood, it can also be used to treat the face of plywood sheets as well. However, for this application, PVA glue is best thinned with a light amount of water, due to its naturally thick composition.

Before applying PVA glue as a sealant, all plywood surfaces should be properly prepared. This involves lightly sanding all surfaces to remove sediment and other imperfections. Once again, the use of a tack cloth is also advisable to further remove fine dust and dirt particles.

Once adequately prepared, plywood can be lightly coated with PVA glue, while being careful to prevent over saturation at any one given point.

PVA glue tends to set quite rapidly, often taking as little as 2-3 hours to fully cure. However, it is also advisable to allow additional time for curing, if the applied coat of PVA glue is relatively thick.

Method #3 – Latex-Based Sealants

latex paint to seal plywood

The application of a latex-based sealant is perhaps the simplest way to waterproof plywood. Paint, in both spray and brush-on forms, is one of the most common sealants applied to plywood. However, latex-based sealant can be found in clear form as well.

A plywood sheet must be adequately prepared prior to being painted. Surface prep of this type is often conducted with the use of sandpaper, as light sanding can be used to quickly remove various surface imperfections.

Ideally, a plywood surface should be completely smooth to the touch before painting commences.

After all prep work is complete, the latex-based paint of your choice can be evenly applied across the entirety of the surface that is to be treated. If this treatment does not provide a satisfactory finish, additional coats of paint can be applied as needed.

Method #4 – Oil Polish

oil sealer for plywood

Though often reserved for use on interior projects, oil-based polishes, such as linseed oil, can be used to seal and waterproof standard plywood sheets. Sealant of this type is quite hearty, though it does require reapplication on a more frequent basis than many other products.

For best results, plywood surfaces should be thoroughly sanded prior to applying oil polish of any type. This removes any contaminants, such as dust and dirt, that might interfere with the application process. When finished, all surfaces should exhibit a smooth, even texture.

See Also: Polycrylic vs Polyurethane vs Lacquer

Oil-based polishes and sealants are typically best applied by brush. Doing so can be quite messy at times, so the use of a catch cloth or basin is highly advised. After thoroughly coating all exposed surfaces, give your newly treated sheet of plywood 24 hours to fully cure, before allowing it to come into contact with moisture of any kind.

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