Plywood has a reputation for being a foolproof, durable material that’s great for building homes and furniture.
However, even plywood needs protection from the elements that can wear away its strength and durability, especially if you want to use it for flooring or outdoor furniture. Depending on the purpose of your plywood, you will need to seal it properly to make the most out of this material.
But what is plywood sealer? There are many different types of sealer that will work well with plywood, including polyurethane varnish, liquid latex, PVA, drying oil, and more. These sealers protect your plywood from moisture, abrasions, and other elements that could ruin it.
This article tells you everything you need to know about plywood sealers and how you can protect your plywood for indoor and outdoor use.
Characteristics Of Plywood
Plywood, an engineered wood, is made from thin layers that are glued together to make each piece of plywood structurally sturdy and very durable. This process helps prevent the wood from splitting when stretched, and it also provides better dimensional stability.
The multiple layers (or “plies”) of wood chips are glued together in a crisscrossing grain pattern. Its strength is enhanced by this construction, so it is stronger, more stable, and more durable than most real woods. It also tends to resist shrinkage and expansion and is considered a highly cost-effective wood, thanks to its durability.
Unlike real wood, plywood is produced according to the shape and size that you need it to be. You can find plywood that is as thick as you want or as thin as you want. In that sense, it is a highly flexible material that is beloved by many woodworkers.
The layers in plywood are glued together using waterproof glue, and the material does have some degree of water-resistant ability. Although it can resist moisture much better than its “real wood” counterparts, it is still porous, so moisture can still seep through the layers, causing warping and splitting.
During its processing, water is used to treat plywood, making the bond between the layers stronger. This process is known as compression – expanding and compressing the wood to strengthen the bonds. However, if plywood gets wet, the wood layers will expand, the bond will become loose, and the plywood will be damaged.
Because of this characteristic, it is highly recommended that you seal plywood with a protective coating so that it can resist the damages caused by the elements, especially water and sun damage.
Why You Should Seal Plywood
Despite being highly durable, sealing is a necessary step to protect plywood from the elements, especially if you are using plywood for outdoor furniture.
Humidity, for example, is one thing that can eat away your plywood slowly, causing molding, rotting, and warping in your plywood. Sealing the plywood with a waterproof sealant will prevent the moisture in the atmosphere from soaking into the plywood, which will protect the plywood from rotting, molds, and even breaking.
Even in a dry climate, dry rotting can still happen. Dry rot occurs when microscopic fungi grow on the wood surface, which may also damage your plywood beyond saving.
If your plywood is to be used for outdoor furniture, sunlight may also damage the wood, twisting the individual plies and discoloring the wood.
If you used unsealed plywood, it would last about 2 years, at most. The untreated wood would rot away within a year because of the sun, rain, and moisture. A sealant will be able to minimize that damage and allow your plywood outdoor furniture to last longer.
Wood also tends to shrink or expand over time. Water exposure can also cause the plywood to split, which is difficult to spot but can completely ruin your plywood furniture. As mentioned above, plywood doesn’t react well with water, so if your outdoor furniture is exposed to the rain and snow, it will slowly break down and lose its shape.
Sealing the wood will also reduce warping and help your plywood look better for longer. Fortunately, sealing plywood is a quick and easy process that you can do over a few hours (or up to 48 hours, depending on the type of sealant you use), and the result will help your plywood look better and help it last longer in your home.
Plywood looks like it has a smooth finish, but it is actually porous, which allows it to bond well to various waterproofing materials. Waterproofing plywood is an easy and quick project that can substantially increase its lifespan. Because of its composition, plywood is very easy to seal.
Waterproofing is especially crucial if you are using plywood for outdoor furniture or flooring because, without the protective coat, you will have to completely replace your furniture once every 2 years – the plywood won’t be able to withstand the elements on its own.
If you are planning on painting your plywood, you should always seal plywood before applying paint. Sealing means coating plywood with a liquid substance that will protect it from the elements, preventing moisture from penetrating the surface and warping the wood, and reducing the possibility of sun damage.
One quick note about sealing is that it is not a permanent solution. Whatever type of sealant you use, you will need to re-seal your plywood after one or two years. Each type of sealant has a recommended time for reapplying the sealant, so you should consider this before choosing the sealant that works best for your purpose.
Best Types Of Sealer For Plywood
There are a lot of sealants that are perfect for helping you add a perfect protective coat to your plywood furniture; let’s take a look at some options below.
1. Polyurethane Varnish
One of the best ways to seal plywood, especially for outdoor use, is to apply exterior polyurethane varnish. This is a very effective sealant that can prevent moisture from entering the wood grain and damaging it.
A polyurethane finish is a type of “plastic” coating that is commonly used for renovation and repair work. Polyurethane varnishes provide high-quality, durable, and stain-resistant protective coatings for wood.
It is designed for long-term durability and hard-wearing protection to various surfaces, such as wooden floors. When applied to plywood, this coating can make the wood waterproof, which will substantially increase the plywood’s durability.
There are two types of polyurethane varnishes, water-based and oil-based. Although both are very easy to use, the water-based polyurethane varnishes have a lower level of Volatile Organic Compounds (or VOCs), which means they give less toxic fumes than their oil-based counterparts.
Moreover, water-based polyurethane varnishes are more durable and easier to use than traditional wood varnishes. They are ideal for woodworkers and restorers and can deliver superior protection for outdoor furniture, including plywood furniture. You can select a glossy, matte, or satin finish depending on your preference.
Although polyurethane varnishes are technically “clear,” the end result may look different depending on your wood and the type of varnish.
Oil-based polyurethane varnishes can leave a light amber finish on the wood. They can also warm up the wood and its grain. One disadvantage of oil-based polyurethane is that it takes longer to dry and contains higher levels of VOCs, which means it is more difficult to use and clean up compared to water-based polyurethane.
High levels of VOCs also mean that it’s generally not safe for children and pets to be around, so you should keep that in mind if you are using an oil-based polyurethane varnish.
Compared to oil-based polyurethane, water-based varnishes are much more popular. When applied, the water-based sealant has a milky color but will dry to a more transparent finish. Because it is water-based, cleaning up can be done with water and soap, which means you can easily use it at home.
2. Water Seal
Some wood stains that are designed to be waterproof, such as Thompson’s Waterseal Waterproofing Stain, make great leaders for plywood. Being a wood stain, it penetrates the wood quickly and easily without blocking the pores in the wood, but it won’t damage the plies.
Thompson’s Waterseal, in particular, is known to be the best type of wood seal for outdoor use. In addition to waterproofing the wood, it also adds a layer of UV protection, which protects the wood from the sun’s damaging effects.
When using this water seal, the brand recommends reapplying the seal once every 1-3 years to keep your wood looking brand new for longer.
3. Liquid latex sealer
Don’t mistake liquid latex sealers for the material that make-up artists use for special effects.
A liquid latex sealer is a great, easy-to-use alternative to traditional waterproofing techniques. Its ability to completely seal a plywood surface in a short time, whether by a spray-on or brush-on method, makes it an ideal choice for creating a waterproof barrier. It sticks on the wood really well and lasts for decades, which means long-lasting protection for your plywood.
However, liquid latex sealers are not very cost-effective to use on a large scale, especially if you want them to perform effectively as intended. Although it is easy to use, it’s difficult to tell whether you have provided sufficient protection for your plywood.
Getting the proper coverage is very important when it comes to protecting plywood because it will help keep moisture from penetrating the plywood, which can damage it. If you are using a spray liquid latex, even spray that provides sufficient coverage is very difficult to achieve, so we suggest using this method only for smaller plywood items.
Polyvinyl acetate (PVA for short) is a synthetic resin that has a rubbery appearance. It is commonly used as glue in woodworking, bookbinding, and other everyday uses. The school glue and white glue that you can often find in stationery stores are usually PVA glue.
PVA glue is known to be odorless and quick drying. It dries clear and bonds well to wood, which means it can be used as a sealer if needed. Since PVA glue has a thick consistency, which can make it difficult to apply evenly, you can add water to dilute it, making it thinner and easier to use.
However, you should keep in mind that PVA is not a 100% effective plywood sealer, especially if you want to use it on outdoor furniture. PVA is somewhat waterproof, but moisture can still penetrate and damage the wood, so you should consider using PVA as a plywood sealer for indoor furniture only.
5. Drying Oil
A drying oil is a substance that hardens to a solid film after being exposed to oxygen. Since many of the sealers mentioned above, including varnish, use drying oil as a key component, you can use a drying oil to seal your plywood effectively. Some of the most commonly used drying oils are linseed oil, tung, poppy seed, and perilla oil.
Drying oils such as linseed oil are great choices for protecting outdoor plywood furniture. Thanks to its ability to soak in the wood’s pores quickly, forming a protective film while keeping the wood’s natural moisture content and characteristics, drying oil is a favorite among woodworkers.
Drying oil is a great way to protect plywood against water damage. It works by creating a protective layer of oil around the wood and strengthening it to prevent rotting. It will also enhance the natural appearance of the wood, rather than changing the wood’s colors and finish, which is very attractive for those striving for a natural finish.
6. Water-Based Paint
If you are planning on painting your furniture anyway, why not use water-based paint? Although water-based paints are definitely not as durable as drying oil or varnish, they will still work as a protective coat for your furniture.
Why water-based? This type of paint can resist cracking and peeling over time, and it can provide a waterproof layer for your furniture. However, you should know that since paint generally doesn’t last as long as other sealers, you will need to refresh it with another coat of paint after 1-2 years.
7. Flex Seal
Flex Seal is a quick and convenient option that can provide a waterproof layer of protection for your plywood. Since it is sprayed liquid rubber, it is pretty easy to apply and can get the job done in no time.
However, as mentioned above, with liquid latex, it’s going to be really difficult to achieve an even coat with a spray bottle. If you want to use it for outdoor furniture, it is not going to provide 100% protection for your plywood.
8. Epoxy Sealer
You’ve heard of epoxy resin used in jewelry making, but it is also a highly effective plywood sealer. Similar to varnish, an epoxy sealant provides a layer of waterproof protection for your plywood. It is very durable and dries clear, which means it can keep the wood looking its natural color.
Epoxy sealer is probably the most effective way to seal plywood for outdoor use since it has the best waterproofing ability. One of the main advantages of epoxy sealer is its ability to resist harsh weather conditions. This is also beneficial for flooring since it can be reapplied without removing the existing layer.
If you want to stain your plywood, you will need to do so before sealing the wood with epoxy since it essentially creates a layer of clear, hard plastic around your wood, which means you can no longer change the color of the wood.
When using epoxy, you should apply it in even layers and spread the liquid epoxy as thin as you can. Then, you can let the resin cure properly, which will take up to 48 hours before the process is finished.
Up Next: The Best Paint For Plywood