How to waterproof plywood for boat

waterproof plywood for boat

Building a wooden boat requires some skill and experience. However, there are things you can do to ensure your boat lasts longer. In this tutorial, we will show you how to waterproof plywood for boats.

When building a wooden boat, it’s important to protect the wood from water damage. Plywood is commonly used for boat construction because it’s lightweight and strong.

However, plywood isn’t impervious to moisture. Over time, the glue holding the layers of plywood together may fail. Water can then penetrate into the interior of the plywood and cause rot.

Throughout this article, you’ll learn about plywood’s vulnerability to water, how waterproofing plywood works, and what types of plywood are available.

Is Plywood Waterproof?

Plywood is best described as being water-resistant, rather than waterproof. Even so, small amounts of water won’t harm plywood, but prolonged exposure to moist conditions can cause it to delaminate or crack. Plywood is made from multiple sheets of wood veneer which are laid and bonded together using pressure and heat.

It’s a very strong material, so any amount of water will only affect the surface layer. But prolonged exposure to dampness can lead to delamination or cracking.

Plywood is often treated with water before it’s manufactured. This process helps prevent moisture from penetrating into the core of the board. When exposed to moisture, the wood expands, causing the layers of veneers to bond together tightly. The result is a stronger piece of plywood.

Plywood is vulnerable because it makes the individual wood layers expand. Over time, this causes the layers to peel apart, separating the layers from each other. This can take many, many years, or just several months, depending on the level of exposure to water.

What happens to plywood when exposed to water is different than what happens with solid wood beams. When a wooden beam is exposed to water, it may soak up the water and eventually deteriorate. However, it does not lose its integrity easily.

Because water separates the layers in a plywood sheet, the effects of water damages are much greater than those experienced by solid wood.

Two other things can occur when plywood gets wet: rot and warping. Rot occurs when the moisture thoroughly corrupts the wood, making it unable to support weight. In plywood, this usually occurs at the location of screws or nails, and the sheets can become completely loose since the wood cannot hold tight to the nail anymore. Warping results in bent, curved boards that look ugly and are useless in any building applications.

Step 1: Apply a Wood Filler

Apply a Wood Filler
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Plywood is used in boat construction for its strength and durability. However, sometimes there are small holes and cracks in the surface. These imperfections can cause problems if you try to paint or stain the plywood. You’ll need to fill those holes and cracks with a wood filler to prevent water damage.

Some types of wood fillers come pre-mixed with a hardener. Others require mixing with a hardener at the time of application. Either way, you’ll need a putty knife to spread the filler evenly across the surface. Smooth it out using the edge of the blade. Don’t worry about getting every last bit of filler off; you only need enough to cover the hole or crack.

Step 2: Sand Down the Plywood

Sand Down the Plywood
Image credit: Daniel Reche, Pexels

Sanding down the plywood also helps to smooth out any uneven areas. If you have an electric sander, use it to get rid of any bumps on the surface. Otherwise, you can use a hand sander to achieve the same effect.

Make sure that when you’re finished sanding, you’ve got a nice smooth finish. It’s not necessary to go too far, but you want to make sure that the plywood has no visible scratches.

Use 80-grit sandpaper to remove any roughness from the surface of the plywood. Continue sanding until you’ve removed all the dust and dirt from the surface. Then, apply the sealant to the plywood.

Apply the sealant to the entire surface of the plywood using a foam brush. Once you’ve applied the sealant, let it dry completely before painting the boat.

Step 3: Clean the Surface of the Plywood

Clean the Surface of the Plywood
Image credit: Ekaterina Belinskaya, Pexels

Removing the dust and debris from the plywood will help to keep it looking new over time. To clean the plywood, use a damp rag to wipe away any excess dust. Make sure that you don’t leave any streaks behind.

Use a towel that is fully soaked with acetone to rub off the dirt. Acetone is a solvent that dissolves organic materials. Rubbing it onto the surface of the plank removes the dirt and grime. Letting it dry for a few hours after rubbing it onto the plank ensures that it doesn’t damage the properties of the plank.

Note: Make sure to let the plank dry completely before applying a layer of sealant. Doing so will prevent any damage to the plank.

Step 4: Apply a Wood Sealant

Apply a Wood Sealant
Image source: Sophia Kunkel, Unsplash

There are several types of wood sealants out there. You’ll want to pick the right one for the job at hand. A brushed-on sealant is probably the easiest option if you’re new to working with wood. It’s simple to apply and gives you a nice finish. However, if you’re trying to waterproof plywood, you may need to use a spray-on sealant instead.

You should only ever use a spray-on wood sealant if you’ve received specific instructions from the manufacturer. Otherwise, you run the risk of either not covering the entire surface properly or having a spotty concentration of sealant. Either outcome won’t work well for your project.

A brushed-on sealant works great for most projects. But if you’re trying to protect plywood against water damage, you’ll need to use a spray sealant instead.

A good sealant will protect the plywood from moisture and make it more resistant to UV damage. There are many different types of sealants available, so it’s important to choose one that is compatible with the type of plywood you’re using.

Make sure that you apply the product evenly across the entire surface of the plywood using a brush. Allow the product to dry for at least 24 hours before applying any additional materials.

Step 5: Use an Epoxy Sealer

Epoxies are great at sealing plywood against the elements, making it strong and durable. You can find epoxies in either liquid form or spray form. The advantage of using epoxy is that it makes the wood stronger, plus it protects it from moisture damage.

You can apply epoxy to the surface of the plyboard using a brush or roller. Once it dries, you can paint over it, any color you like. However, if you run a little sandpaper over the dried product, you’ll still be able to paint over it.

Which Plywood to Choose for Outdoor Use?

Plywood is used for decking, flooring, siding, and exterior walls. You’ll find two main categories of plywood: CDX and marine-grade. Both are great choices for outdoor use, but there are differences between the two.

CDX plywood is made of rough, low-quality wood that is heavy-duty and highly resistant to moisture. It’s ideal for things like roof shingles, decking, and interior wall panels. However, CDX isn’t meant to stand up to harsh weather conditions. So if you live in a coastal region where storms are common, you should consider using marine-grade plywood instead.

Marine-grade plywood is smooth and high-quality, making it ideal for outdoor applications. It’s designed to withstand extreme weather conditions, including saltwater exposure. Because it’s smoother, it won’t crack or splinter like CDX plywood does.

Both types of plywood are excellent options for outdoor use. But if you live in a humid climate, marine-grade plyboard is the best choice. It’s less susceptible to cracking and splitting than CDX plywood.

Types of Waterproof Plywood

  • ABX Plywood
  • ACX Plywood
  • ADX Plywood
  • BWP Plywood
  • MR Grade Plywood
  • BWR Grade Plywood