Can Plywood Get Wet During Construction

Can Plywood Get Wet During Construction.

Can Plywood Get Wet?

Plywood is an engineered or manufactured type of wood used for everything from walls to piece of furniture.

From its long-term employ in an outdoor project to the risk of information technology getting moisture during the trip abode from the lumberyard, a common question people oft have is whether or non plywood can go wet, and that’s what we’ll exist discussing in this article.

Plywood can get wet, and short, isolated periods of moisture should non cause any long-term damage. Standard plywood is not waterproof, though, and the utilise of marine plywood or a waterproofing sealant is recommended to prevent rot in specially wet conditions, for example, from outdoor use.

Read on to find out more about what happens when plywood gets wet, what you tin can exercise to both dry out and flatten warped plywood, and 3 ways you can waterproof your plywood for outdoor use.


  1. Is Plywood Waterproof?
  2. Can Plywood Exist Used Outdoors?
    1. Plywood That Will Be Exposed to Moisture
    2. Plywood That Will Be Exposed to Sunlight
  3. What Happens if Plywood Gets Wet?
  4. How Long Will Untreated Plywood Last Outside?
  5. How Practise You Treat Wet Plywood?
    1. How to Dry Plywood
    2. How to Flatten Warped Plywood
  6. How to Brand Plywood Waterproof
    1. Painting
    2. Epoxy Sealing
    3. Applying Oils
  7. Final Remarks

Is Plywood Waterproof?

Plywood is non waterproof as standard.

If you’re planning on using plywood outdoors where information technology’s probable to encounter moisture, either from the odd bit of pelting or where it’ll be left sitting in continuing water, there are a few unlike choices bachelor:

  • Applying a protective layer in the form of paint, epoxy sealant, or oil to protect the wood from the elements.
  • Alternatively, you could employ an exterior grade sheet, for example, marine plywood or pressure-treated plywood, for protection in particularly wet conditions (although nosotros’d still recommend applying a sealant for extra moisture resistance).

If yous opt to forego sealing your plywood or choose not to use exterior grade plywood, it’southward probable to rot and decay when exposed to moisture for extended durations.

The nearly common form of deterioration in plywood exposed to water is delamination, where the gum between the various layers fails, causing portions of the plywood sheet to pare abroad.

Another matter to spotter out for with plywood is the gum used between its plies or layers, which can be either interior or outside class glue.

A common misconception is that if plywood uses outside course glue, the wood is waterproof and suitable for outdoor utilise, but this isn’t always the case.

For case, diverse types of birch plywood and baltic birch plywood sheets apply exterior class glue, and these aren’t waterproof as standard.

Without some grade of sealing, the wood layers will still absorb water as with regular plywood, leading to rot and delamination (in other words, when the layers start to split).

Can Plywood Exist Used Outdoors?

You can use plywood outdoors, just you’ll need to match the extent of the treatment you apply or the specific blazon of plywood you opt to utilize to the conditions that it’due south likely to meet.

Plywood That Will Exist Exposed to Wet

Volition the plywood exist subjected to the odd bit of rain and standing water, or will it be fully submerged in water, for instance?

In other words, how wet is the plywood probable to become?

The exact conditions will dictate whether a finish such as painting or epoxy sealing will be advisable or whether you’ll demand to utilise marine or pressure-treated plywood to ensure it tin withstand the elements.

For less extreme conditions, such equally occasional exposure to rain that won’t have the gamble to puddle or pool on the plywood, we’d recommend waterproofing the plywood with paint, epoxy sealant, or oils to prevent water-related harm.

Y’all probably don’t need to get to the extreme of using marine or pressure-treated timber for plywood exposed to occasional rainfall, as in many cases, the sealant layer should exist sufficient to prevent moisture ingress and damage to the plywood. Yous volition probable demand to reapply the sealant layer every few years or so, yet.

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For the wettest applications, marine or pressure-treated plywood is probably the best option. To provide maximum protection, nosotros’d recommend applying an boosted layer of sealant, whether in the form of paint, epoxy sealant, or oil that blocks the pores in the plywood and prevents wet ingress.

Plywood That Will Exist Exposed to Sunlight

Exposure to sunlight, and the subsequent damage this can lead to, is another of import gene that you need to consider when using plywood outside.

In his article, Paint, Forest and Conditions, good Colin Mitchell-Rose explains that untreated wood, including plywood, will gradually deteriorate when exposed to sunlight for long periods.

At the risk of getting overly technical, this is acquired past cellulose (1 of the principal components in the various layers that brand upward a plywood sail) undergoing a process known as
due to the UV radiation that comes from sunlight.

The typical result of this process is the graying of the plywood’s surface, with the color fading due to surface bleaching.

Thankfully, in most cases, the impairment from sunlight is purely cosmetic, as the fading merely occurs in the layers close to the surface, meaning that it shouldn’t touch the strength or structural integrity of the plywood.

I of the easiest ways to forestall sunlight-related damage in plywood is by applying a sealant layer to the surface.

What Happens if Plywood Gets Wet?

Plywood is renowned for its dimensional stability, and this means that it is much less susceptible to shrinking, swelling, or warping versus other types of timber.

The principal source of plywood’s dimensional stability is its alternating layers or plies, which are glued together, and this likewise results in alternating grain patterns throughout each canvas.

You tin can come across the alternating grain patterns in the image below:

an image showing the various plies or layers in plywood


By contrast, non-engineered, conventional types of lumber typically feature a grain that runs in i direction just throughout their entire depth, and this is less dimensional stable than plywood as a result.

Let’s look at a piece of two×4 that is left sitting on wet basis every bit an example.

Provided it isn’t raining, the side facing upward volition inevitably dry out faster than the side left in contact with the moisture ground.

As the elevation dries, it shrinks faster than the bottom face, and this procedure tin cause stresses throughout the forest leading to cupping or bowing.

Plywood tin resist these stresses better due to the motility beyond the various alternating grain patterns, effectively cancelling each other out.

Considering of this, plywood is proficient at coping with low amounts of wet, and it takes a lot more than wet and internal stresses to cause warping versus conventional lumber.

This only occurs upwards to a certain point, though, bold that y’all’re using conventional plywood that hasn’t been sealed versus a pressure-treated or marine plywood.

High levels of exposure to moisture in unsealed plywood, such as leaving sheets on wet ground for long periods, tin be a massive issue leading to cupping and bowing problems in the short term and rot and delamination in the longer term.

An example of delaminated plywood is shown below:

an example image showing what happen to plywood when it gets wet and rots


Information technology’s also important to recall that woods is biodegradable, and plywood is no exception.

In a higher place effectually a 20% moisture level, plywood can experience damage from various types of mould, fungi, and even sure species of beetle that can significantly damage the forest.

How Long Will Untreated Plywood Terminal Outside?

Nosotros’d estimate that untreated plywood would last anywhere from between two to five years exterior.

The exact length of time volition be influenced by a variety of factors, including:

  • The thickness of the plywood sheet, with thicker sheets likely lasting longer.
  • The status of the plywood prior to beingness left outside, with whatsoever areas of impairment caused during initial transportation or storage potentially accelerating deterioration.
  • The presence of any defects like knots or voids that could assist with wet ingress and further speed upward deterioration.
  • The corporeality of ultraviolet rays from direct sunlight that the plywood is exposed to, with a quicker fading or ‘graying’ of the plywood’s surface in more than extreme atmospheric condition.
  • The plywood’s exposure to moisture, ranging from occasional contact with rain to sitting in continuing water, with more exposure leading to faster deterioration, especially in untreated plywood.

In terms of what kinds of damage will occur and when, the first signs of deterioration would probably be the fading or ‘graying’ of the plywood caused by exposure to ultraviolet rays in sunlight.

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Warping would then occur in unsupported timber sections over fourth dimension, followed by splitting and delamination that could cause significant reductions in the plywood’s strength.

How Exercise You lot Care for Wet Plywood?

We’ll discuss how to treat or waterproof your plywood in the adjacent section, but it’south worth roofing the steps you need to take beforehand if you want to work with plywood that’s already moisture.

There are two steps that nosotros recommend:

  1. Get-go, you lot need to let the plywood dry out out.
  2. 2d, you need to flatten the plywood if information technology is warped.

Let’s look at each step in more particular:

How to Dry Plywood

If your sheets are both warped and wet, information technology’s probably best to sort the moisture upshot kickoff.

A common question is how long plywood takes to dry, and depending on how wet your plywood is to get-go with, it can take anywhere from a few days to weeks to dry out out.

Here’south how we typically dry out wet plywood sheets:

If you’re working with single sheets, we’d recommend placing each sheet on at least iii supports (ensure these are equally sized and level) on the floor.

Raising your plywood off the ground in this fashion will allow air to broadcast nether the sheet, ensuring that both the top and bottom faces have a good chance of drying out.

If yous want to dry out out more than one sail, you can identify another iii supports on top of the commencement sheet (make sure these line up with the supports on the floor propping up the first sail), so go ahead and stack your second canvass on elevation.

Information technology’s possible to keep stacking more sheets in this style, but be careful and brand sure there’south no take a chance of the sheets toppling over.

It’due south normally a practiced thought to move the position of the supports every and then often, as this allows the surface area that was in contact with the sheet also to dry out out.

We’d recommend running a cloth or sponge over the sheets earlier stacking to remove nigh of the moisture, and if y’all’re able to, placing the sheets somewhere with a heat source or dehumidifier will speed upwards the drying process.

Leave your sheets stacked like this and cheque them periodically to see how the drying process is going. Recollect, they might appear dry on the surface, but they could still be wet internally, so allow extra time for the sheets to dry out fully.

How to Flatten Warped Plywood

Now that your plywood sheet is fully dry, the next stride is to flatten the sail and remove whatever warping.

Here’s what we recommend depending on the caste of warping:

For Pocket-size Warping

When information technology comes to flattening out small-scale warping, our go-to method is sandwiching the bowed plywood between two flat sheets of wood (this could exist plywood, MDF, or any else y’all tin find).

You can also sandwich the lath between flat ground and a 2d board if you don’t have enough cloth to hand. In this case, we’d recommend placing a polythene sheet between the plywood and the footing to foreclose any moisture ingress if the ground is moisture.

Regardless of the pick you choose,
make sure your plywood sheet is placed bow side up, every bit shown below.

an example image showing how to flatten warped plywood

You lot might as well need to add some weight to the top sheet to provide enough downwards pressure to flatten the warped plywood.

We usually go out our plywood in this ‘sandwiched’ state for a couple of days, and we come up dorsum every so often to check on progress.

For More Astringent Warping

For plywood with more than severe warping, we adopt a slightly different process.

The first step is to place your plywood sheet on two supports, with the warp going upwardly as shown here:

an example image showing how to flatten warped plywood

Next, to account for the difference in moisture between the two faces of the plywood, spray a light mist of water across the concave confront of the sheet (the bottom face up in the example above).

Yous’ll then need to apply weight to the crest of the warping (the point where the warping is at its worst), which is close to the center of the plywood sheet in the example above.

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The weight shouldn’t exist so heavy that yous run a risk breaking the plywood, but
information technology needs to be heavy enough to offset to flatten the sheet out noticeably.

From nipped fingers to dropping weights on your feet, there are enough of risks here, then exist sure to pay attending to your rubber.

When working with thicker sheets or more severe warping, the weight you’re using volition demand to be increased to make a divergence.

We’d recommend checking on your plywood every 60 minutes or so to gauge progress. Y’all’ll know that information technology has been successful if the sail no longer springs upwards when you remove the weight.

How to Make Plywood Waterproof

As discussed,
untreated plywood will rot and deteriorate if left exterior for extended durations, and this is the case for all types of plywood, from the cheapest varieties to the most expensive baltic birch.

And then, whatsoever you lot’re using plywood for outdoors, from panelling to outdoor article of furniture, you’ll need to have a few steps to waterproof it before use to prevent whatever water-related damage.

It’due south also worth begetting in mind that different levels of finishing may exist required before waterproofing your plywood, and this is due to the fact that there are multiple ‘grades’ available.

Lower-grade, cheaper plywoods, for example, might take more surface-level defects like knots and voids, which need to be filled and sanded earlier applying a sealant or waterproofing coat.

Once finished to an adequate standard, there are iii main options available for waterproofing plywood:


Painting is one of the most mutual means of waterproofing plywood, and information technology’southward also one of the cheapest.

H2o-based acrylic latex paints or epoxy paints are the most mutual.

Although not 100% essential, we’d recommend using a primer starting time to seal the wood, as this provides a ameliorate opportunity for a high-quality finish.

Using a primer can as well reduce the corporeality of overcoat needed as the plywood tends to absorb less of the primer than the overcoat. It can provide a better bond for the overcoat versus painting directly onto the plywood, as well.

Some modern paints consist of a combined primer and overcoat, which saves time and effort applying a separate primer layer. These are usually more expensive, so yous probably won’t relieve as much equally you’d recollect versus buying split up paints.

Epoxy Sealing

Another selection for keeping plywood dry out and in proficient condition exterior is by applying a layer of epoxy resin that will create an impenetrable barrier between the wood and the elements.

Unlike epoxy paint which applies a colour, epoxy sealing products are typically clear, allowing the plywood to keep its natural advent.

An added reward of applying epoxy resin is that information technology drastically increases the hardness of the woods, improving overall immovability.

Applying Oils

In addition to providing a sure level of wet resistance, some oils, for example, linseed oil, can change the appearance of plywood through low-cal staining.

However, some oils like tung oil dry clear, which will leave the plywood’southward original appearance unaffected.

These oils work by penetrating the plywood’s surface to provide a layer of protection from the elements.

It’s important to empathise that multiple layers of oil may be required. Exposure to the elements tin can cause the oil to dry out out, meaning it will demand to be reapplied periodically to continue to provide optimal waterproofing.

Terminal Remarks

Standard plywood is not waterproof, and it’ll need a layer of protection in the form of paint or an epoxy or oil sealant to prevent moisture-related damage when used outdoors.

We’d recommend using marine or pressure-treated plywood where high moisture levels are possible, for example, in especially humid conditions or applications where continuing h2o is probable. In these cases, nosotros’d still recommend applying a sealant for additional waterproofing.

It’s of import to remember that untreated plywood can typically last for between two to v years outside, and this is due to its dimensional stability that resists a lot of the shrinking, swelling and warping common in natural timbers.

Because of this, yous don’t need to worry almost isolated or one-off situations where your plywood gets moisture briefly, for example, when transporting it home from the lumberyard or dwelling house improvement store. Every bit we’ve shown in this commodity, provided you deal with it as quickly as possible and allow information technology dry out out equally a priority, there shouldn’t be whatsoever lasting bug.

Can Plywood Get Wet During Construction