How to Waterproof Plywood: Tips for Beginners

Many DIY workers and house owners wonder how to weatherproof plywood at home. Plywood is a durable and reliable material that is widely used in remodeling and building.

This product is in favor of both professionals and amateurs for its ease of use and longevity. Besides, plywood is less expensive than other materials and types of wood.

Although it looks like the best choice due to the numerous features, this material is extremely vulnerable to bad weather and moisture. To avoid unnecessary expenditures on new materials, you have to learn how to seal plywood for outdoor use. It will save the product from decay and improve its endurance.

Detailed Guide on Weatherproofing Plywood

Weatherproof Plywood

Here is a detailed review of how to make plywood last outside. If you don’t want to buy another material just after the plywood was ruined by water, you should learn some tricks. Don’t worry, they are not expensive, and some of them will cost you nothing.

Why do you need to weatherproof plywood?

Sealing or weatherproofing plywood extends the life of the material in the first place. Apart from it, this procedure has several benefits. Check the major advantages below.

Rotting prevention

If you want to secure the material from mold and further rotting, you have to waterproof plywood. It is common for almost all exterior woods to get damaged by this problem. Rotting does not only spoil the perfect outside look, it makes the whole wood fragile and brittle. Seal the plywood to get rid of mildew.

rotten plywood

Moisture and sun protection

Water might cause rotting, but this is not all damage it does. Once the water gets to this material, it might break the whole structure from the inside. In the end, the plywood will be torn apart. To protect it, you have to use plywood sealant as soon as possible.

Sunbeams might look gleaming on the newly bought plywood, but after some time, they might cause damage. Several hours a day under the intense sun, and the wood starts twisting. It might lose its color and shape. To save its appearance, make sure sun rays and water have no access to the plywood.

Splitting protection

After you seal the plywood, the chances of splitting significantly reduce. It protects materials from shrinking, keeping them solid. This procedure decreases the possibility of wood warping.

How to seal plywood for outdoor use

Here are a few simple steps that allow you to protect newly bought plywood. Check them out:

  • Start sealing plywood edges with the 80-grit sandpaper. Move back and forth to sand it down evenly. Try to make moves along the wood’s natural grain so that it isn’t splintered or damaged;
  • If you want a smoother finish, you can use the 120-grit measurement of sandpaper. Just keep in mind that the higher the grit level you pick, the more effort you have to put. Still, the plywood will be smoother. I don’t recommend using more than 120-grit paper since it can damage the whole structure of the material;
  • Wipe the plywood dust that is left from the sandpaper with the towel or cloth. The area must be clean;
  • Pick the paintbrush for the sealer. Don’t use the widest brush in your collection. The middle or small sizes would be better;
  • Take the plywood sealer and apply it making smooth and even strokes with the paintbrush. Try not to miss a spot. If you are not sure whether you have covered everything evenly, make another round. Let the sanding sealer get dry for some time. After that, you can seal the plywood from the other side;
  • After both sides are dry, use 120-grit sandpaper again. Don’t press too hard. Slightly move back and forth. These moves will remove any unevenness and airspaces. Stop when you feel that the surface is smooth;
  • Apply the sealer in a final coating. Give it some time to dry. This finish will hold for years.

Techniques for weatherproofing plywood

Before you use this material outdoors, make sure the flex seal on plywood holds reliably and withstands any weather. No matter whether it is sun or rain outside, sealing has to make the wood everlasting.

You don’t need to call professionals. These methods are simple to perform even if you work alone. Meanwhile, make sure you have up to 2 days to finish the weatherproofing.

Polyurethane varnish

Sealing the edges of the plywood is a whole separate process that requires your attention. The best-known way to do this is by using the polyurethane varnish technique. You need:

  • Varnish;
  • Brush. Make sure it is small;
  • Masking tape.

Apply the varnish to the wood’s edge, using a small brush. Don’t touch the plywood’s surface. Now use the masking tape to cover the surface. The entire coverage prevents the varnish from spreading.

If you let the varnish get on the surface of the plywood, it will become unable to absorb any treatment in the future. Wait half an hour before you apply another layer of varnish. You can put as many layers as you want. It will protect the edges from water and other weather changes.

Water-based stain

Water-based stain is the quickest way to cover the entire plywood’s surface. The stain is almost unnoticeable. It works splendidly against UV rays and rain. You need:

  • Cloth rag;
  • Sprayer;
  • Water-based pigment stain.

You might already have the pump-up sprayer in your garden. Use it to apply the coating. Leave it there for 10-15 minutes. Check out the time on the container of the water-based stains.

After everything gets dry, use the rag and clean the excess. The stain does not have to completely cover the plywood. Yet, it will change the color into a lighter shade and protect the material. After you apply this stain, you can leave the plywood to dry for 24 hours before using it.

Water seal

If you live in an area with a high moisture level, you have to use this technique. While it saves the plywood, it does not block the pores. You need:

  • Garden sprayer;
  • Water sealant.

Take the sprayer and fill it with water sealant. Now cover the plywood with it. Once the surface gets smooth, apply another layer. Repeat the procedure several times to receive the result.

Professionals advise to re-apply the sealant every 2 years. You can choose the sealant you need in any paint store or order it online.

Related post: Best Fence Stains & Sealers

Which plywood is best to use outdoors

The market offers you a wide range of plywood manufacture types. You need the one that is the most suitable for your intentions. The most popular type of plywood that is used outdoors is CDX. Many people also use T1-11, OSB, pressure-treated, and marine-grade options. They are all different.

CDX comes with 3, 5, 7, and 9 piles. It is used in the roofing and construction industries. Marine-grade plywood is mainly used for porches and decking. A pressure-treated one is easy to recognize by the oily surface. It is covered with numerous chemicals that prevent mildew and rotting. OSB suits roof decking the most. T1-11 is usually bought for sidings.

No matter which type you choose, you can paint it up to your preferences. To save some money, you may choose CDX material. For objects that will touch the water or stand near the water, you need a marine-grade type.

FAQ About Plywood Weatherproofing

Plywood before Waterproof

I have gathered the most frequently asked questions about the waterproofing of wood here. I hope you will read my answers before you decide on which method of plywood protection to use. Check them, and if you have something to add, do it in the comments.

Do you need to weatherproof plywood?

Despite all the benefits of plywood, this material must be water-sealed in advance. Some types of this material, like marine-grade and pressure-traded, are already covered with a protective coating. Yet, you still can put extra layers to prevent the possible damage from moisture if you use plywood outdoors.

What to put on plywood to make it waterproof?

I have described all the best ways to protect the surface of the plywood and its edges. Use polyurethane varnish for edges and water-based pigment stain or water sealant for plywood surfaces. You can change the methods; all of them are decent and effective.

Can you paint plywood to make it weatherproof?

This type of waterproofing is the most widespread. However, I recommend using a specific waterproof coating before you paint the plywood. Some modern paints already have waterproof ingredients inside. Check them before you buy them. In this case, you don’t need extra security.

Seal Plywood for Years

I hope my detailed review of methods, types, and benefits of weatherproof remedies will be helpful for you. Since they are not expensive, you may use all of them in your work. Pick the sealer after you decide on which plywood you want to buy and use in your work.

Don’t forget to use a protective mask and gloves while working with plywood and chemicals. It will save your skin from itching. If you have weatherproofed plywood before, share your impressions in the comments below.

How effective were your efforts? Which method did you use? Which type of plywood do you use the most frequently?

My ultimate goal is to provide insights that will help you effectively determine whether this or that tool or product suits your needs/budget or not. I test out home improvement tools at work on a daily basis and enjoy sharing my knowledge with D.I.Y-ers who have similar questions to the ones I used to have. I realize how important choosing the right tools is, that’s why my approach to every review I publish is very responsible.

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