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Can Baltic Birch Plywood Be Used Outdoors?

One of the most important things to consider when choosing a material for an outdoor project is its ability to withstand environmental conditions.

The material must handle rain, sun, wind, and snow without losing any strength or stability if it’s to be truly effective.

Baltic birch plywood is a strong, durable wood that can be used for many different things. One question people often have about it, though, is whether or not it can be used outdoors.

Can Baltic Birch Plywood Be Used Outdoors? – The Quick Answer

Baltic birch plywood cannot be used outside as standard. Despite baltic birch plywood often using exterior grade glue between its layers or plies, the wood itself is not waterproof. If used outside without proper sealing, baltic birch plywood will absorb water leading to rot and delamination.

So, before you go and spend your hard-earned cash on one of the most expensive types of plywood out there, let’s figure out whether baltic birch is the right kind of plywood for your outdoor project.

Is Baltic Birch Plywood Waterproof?

Before answering this question, it’s worth mentioning that there are two main types of ‘birch plywood’.

  • Firstly, there’s plain old birch plywood, sometimes referred to as veneer birch plywood, which is manufactured throughout the world.
  • Secondly, there’s baltic birch plywood, which is primarily produced in Finland and Russia (these countries are located close to the Baltic Sea, hence the wood’s name).

The main difference between the two is quality, with baltic birch typically having twice the number of ‘plies’, or layers, as the conventional birch variety.

It’s because of this that baltic birch plywood is considerably more expensive.

an image showing the various plies or layers in birch plywood that are susceptible to water damage when used outdoors

The plies in baltic birch plywood are almost always birch wood throughout, too, as opposed to poplar or some other cheaper hardwood that’s sandwiched between two layers of birch in conventional birch plywood.

The confusion as to whether or not birch plywood (or baltic birch plywood for that matter) is waterproof often comes down to the grade of glue used.

Both types of plywood can be made with either interior or exterior grade glue, with the exterior classification often making people think the wood itself is waterproof and suitable for outdoor use.

This isn’t the case.

Neither birch plywood nor baltic birch plywood is waterproof even if exterior grade glue has been used.

Without proper sealing, the wood layers will absorb water leading to rot and delamination (in other words, where the layers separate).

What Happens When Baltic Birch Plywood Gets Wet?

One of the biggest benefits of plywood is its dimensional stability, which is primarily due to its pattern of alternating layers (and resulting alternating grain patterns).

By contrast, most other types of timber feature a grain that runs in a single direction throughout its entire depth, with this being less dimensionally stable.

Let’s look at a 2×4 that gets wet as an example.

As it starts to dry, one side of the part will inevitably end up drying faster than the other – this could be the top side, for example, which faces direct sunlight while the bottom side sits directly on the wet ground.

As the top dries, it shrinks faster than the bottom, with this process causing stresses on the timber, which can change its shape through cupping and bowing.

On the other hand, baltic birch plywood can better cope with low-level moisture changes, which is due to any movement in the wood’s alternating grain patterns effectively cancelling each other out.

This only occurs up to a certain point, though.

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

It’s important to remember that wood is biodegradable, and baltic birch plywood is no exception.

Above around a 20% moisture level, the plywood can undergo damage from different types of mould, fungi, and even certain types of beetle that can significantly damage and weaken the wood.

How Long Will Untreated Plywood Last Outside?

A rough estimate would be between 2-5 years.

Many variables affect how long untreated plywood can last outside, though, including:

  • The thickness of the plywood sheet
  • Its condition prior to use (for example, if it was already bowed or warped)
  • The presence of any defects like knots or voids that could assist with moisture ingress
  • Its exposure to ultraviolet rays from direct sunlight
  • Its exposure to moisture, ranging from occasional contact with rain to sitting in standing water

For regular outdoor usage, the first signs of deterioration would probably be the fading or ‘graying’ of the plywood from exposure to ultraviolet rays in sunlight.

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

How to Make Birch Plywood Waterproof

As mentioned above, untreated plywood will rot and degrade if left outside for long periods, and this happens in everything from the cheapest varieties to the most expensive baltic birch.

So, whatever its outdoor application, from panelling to outdoor furniture, it’s critical to waterproof your birch or baltic birch plywood before use to prevent any water-related damage.

It’s also important to remember that depending on the grade of plywood you’re using, different levels of finishing may be required before waterproofing.

It’s also important to remember that depending on the grade of plywood you’re using, different levels of finishing may be required before waterproofing.

Lower-grade, cheaper baltic birch plywoods, for example, might have more surface-level defects like knots and voids, which need to be filled and sanded.

After finishing, there are three main options available for waterproofing baltic birch plywood:

1. Painting

Painting is one of the most common ways of waterproofing baltic birch plywood, and it’s also one of the cheapest.

Water-based acrylic latex paints or epoxy paints are the most common.

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

Using a primer can also reduce the amount 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, too.

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 you probably won’t save as much as you’d think versus buying separate paints.

2. Epoxy Sealing

Another option for keeping plywood dry and in good condition outside 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 color, epoxy sealing products are typically clear, allowing the plywood to keep its natural appearance.

An added advantage of applying epoxy resin is that it drastically increases the hardness of the wood, improving overall durability.

3. Applying Oils

In addition to providing a certain level of moisture resistance, some oils, for example, linseed oil, can change the appearance of plywood through light staining.

However, some oils like tung oil dry clear, which will leave the plywood’s 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 understand that multiple layers of oil may be required. Exposure to the elements can cause the oil to dry out, meaning it will need to be reapplied periodically to continue to provide optimal waterproofing.

  1. Does the sun affect baltic birch plywood?

Yes, baltic birch plywood can be affected by sunlight.

In his article, Paint, Wood and Weather, expert Colin Mitchell-Rose explains that wood, including baltic birch plywood, will gradually degrade from prolonged exposure to sunlight.

This is because cellulose, one of the main components in the various layers making up a baltic birch plywood sheet, experiences something known as auto-oxidation as a result of the UV radiation that comes from sunlight.

This leads to the graying of the plywood’s surface where the colour has been faded due to surface bleaching.

In most cases, this graying is purely cosmetic, as the fading only occurs to plywood plies close to the surface mean that it shouldn’t affect the plywood’s overall strength.

  1. Are there alternatives to baltic birch plywood for outdoor use?

When considering alternatives to baltic birch plywood for external use, it’s essential to think about how wet the wood is likely to get.

For example, will it have continual exposure to or immersion in water, or does it only need to withstand the likes of occasional rain and the sun’s ultraviolet rays?

For the wettest applications, marine plywood is probably the best option.

For less extreme conditions, baltic birch plywood featuring one of the above waterproofing options, pressure-treated plywood, or medium-density overlay (MDO) are probably likely alternatives.

Final Remarks

As you can see, there are plenty of things to consider when it comes to using baltic birch plywood outside.

We hope we’ve shown you that it is possible to protect plywood from the elements and that you’re now better informed to choose the right type of finish to protect your plywood project against any weather-related damage.

If you have any particular questions or queries that you can’t find an answer to above, drop us a comment below, and we’ll do our best to get back to you as quickly as possible.

Thanks, and good luck with your outdoor project.

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Author: Jon Maxwell
Senior Writer, ToolCrowd
Jon Maxwell writes about various topics for ToolCrowd, including tool reviews, material advice, common home problems, and general DIY advice and how-to articles. His work has been published in national publications for audiences including consumers, homeowners, and industry experts. Jon has a bachelor's degree in Building Surveying and a master's degree in a branch of Civil Engineering focusing on concrete and steel durability. When he isn't writing for ToolCrowd, Jon enjoys completing DIY tasks in his own home, as well as woodworking in his home workshop, snowboarding, and website development. Contact Jonarrow_right_alt