Wood Working

Ronaldphillipsantiques – Plywood is one of the strongest and long-lasting materials used for house building and remodeling. Many DIY workers also prefer this wood because of its longevity. Plywood is also affordable compared to many other kinds of wood. Unfortunately, it is a known fact that exterior plywood is vulnerable to moisture.

To prevent it from surface cracking, plywood demands sealing which not only saves it from water damage and decay but also ensures its long-term performance and endurance.

After sealing, the woodwork is finished with paint or some kind of strong resin such as polyurethane. The required tools for sealing of plywood can be easily found in any hardware store. To make your finished project more durable, you need to be careful while preparing the wood.

However, the sealing project can be sometimes tricky when it comes to sealing rough surfaces. Don’t worry! Our step by step guide on how to seal plywood for outdoor use will assist you even with sealing rough surfaces.

Benefits of Sealing Plywood

Benefits of Sealing Plywood

Sealing plywood has any advantages. It will save you from extra expenditure and your wood from decaying.

1. Prevention of Rotting

All exterior woods are prone to gel mold due to its nature and other factors like humidity. a rot makes a wood damaged and also destroys its appealing look. Rot can be developed on ply-wood in various ways. The best way to protect it from any type of mildew is by sealing it.

Sealing ply-wood properly and efficiently will save you from future trouble.

2. Protection From Sun and Moisture

If water penetrates plywood, it just not only cause rot. Extra water penetration can cause wood to break. This can largely damage your plywood material. To prevent it from happening, seal your wood as soon as possible.

Sunlight rays also damage the wood. More intense exposure to the sun will result in the twisting of wood. This can cause wood to lose its natural beauty and structural integrity. Sealing plywood will help to maintain its structure and appearance.

3. Balance Sheet

Sealing wood will reduce its chances of splitting. Sealing keeps plywood strong and prevents it from shrinking, expansion and twisting. A balanced wood surface will reduce the chances of wood warping.

How to Seal Plywood for Outdoor Use: Step by Step Guideline

Following are some steps taken during sealing of plywood:

  • First, all sides of plywood are sanded by using sandpaper of 80-grit measurement. It is better to sand in back and forth motion and along the natural grain of the wood rather than across the natural grain.
  • To get a smoother finishing touch, sanding is repeated with 120-grit sandpaper. Sandpaper of higher grit can also be used for an even better smooth finish but in the case of plywood, it is not required.
  • By using a clean cloth, plywood dust is wiped off. For applying a sanding sealer, a dust-free and clean area is required. You also need a clean paintbrush to apply the sealer.
  • With the help of a clean paintbrush, sanding sealer is applied on the plywood in even and leveled brush strokes to coat the surface. Unevenly coating saturates the surface making it rough. The essential element for a proper and smooth finish is even coating. Let the coating of sanding sealer dry, as instructed by the manufacturer. If you wish to seal both sides of the plywood, do it in steps. First, finish one side and let it dry. Then seal the second side.
  • Now, the sealed surface is again sanded using 120-grit sandpaper. This light sanding removes the bumps caused by the first sanding and cause airspaces (left from sealing) to diminish. Sand till you get a smooth touch but without damaging the sealing. This causes the plywood to appear waxy.
  • In this step, a final coating of the sanding sealer is applied and allowed to dry. This gives plywood a long-lasting finish.

3 Common Technique For Outdoor Plywood Sealing.

Plywood Protection Tips

To ensure a long life of plywood outside, it is necessary to weatherize it. You can simply do it by yourself with the help of the following methods. This whole project will just require only 1-2 days.

1. Polyurethane Varnish

One of the best methods to seal plywood edges outside is by applying exterior polyurethane varnish. You will require the following materials.

  • Small brush
  • Varnish
  • Masking Tape

Apply a coat of polyurethane varnish to the edge of a wood with the help of a brush. Avoid it using on the surface of the plywood. Cover the surface with masking tape. Do a full coverage with tape to block varnish.

If varnish gets a hold on the plywood surface, it will not allow the wood to absorb any future wood treatment. Now after 1st coat, wait for 30 minutes. After that, apply several layers of varnish for the best results.

This treatment of plywood edges will prevent it from water penetration. It also helps to save it from dreadful weather conditions.

2. Water-Based Stain

Cover the entire surface of the plywood with a coat of any exterior water-based stain. These stains are very light in color and do not show any bright shade. These work best for protecting the surface against strong UV rays. Grab the following material

  • Pump-up Sprayer
  • Cloth rag
  • Water-based pigment stain

With the help of a garden or pump-up sprayer, apply the stain. Allow it to dry for several minutes. Drying time will always be mentioned in the stain container. For best results, follow the mentioned timeline.

After spraying the whole surface, use cloth rage to clean any excess or dripping stain. Keep in mind, this water-based pigment stain is not proposed to completely paint your plywood. They will give a light color and protection to your wood from sun damage.

For the best effect, leave your wood for at least 24 hours after applying the stain coat.

3. Water Seal

This sealer is great for guarding plywood against water penetration. It is a good wood conditioner and doesn’t block all pores of the wood.

Things you will need are as follows.

  • Water sealant
  • Garden sprayer

Take a garden pump-up sprayer. Apply a coat of water seal to your plywood. After smoothing the surface, apply another coat. Use several coats of sealant to get a maximum result against water penetration. It is best to reapply sealant after every 2 years.

A wide range of water sealants can be easily found in any kind of paint store. They usually come under manufacturer’s names.

Which Plywood to Choose For Outdoor Use?

There is a variety of exterior plywood and it is important to know which one will benefit you the most. If not selected properly, sealing will not be useful. It will be prone to become rotted, soft, and break. The most common types of exterior plywood are CDX, marine-grade, pressure treated, OSB, and T-11.

Marine-grade exterior plywood has knot-free sheets and is mostly used for decking, porches, planters, and arbors. CDX is the most commonly used plywood. It normally comes in piles of 3, 5, 7, 9, and the lowest number indicates the uppermost class of a CDX plywood. They are widely used in the construction industry and for the roofing of buildings.

Which Plywood to Choose

Pressure-treated exterior plywood can be identified by its oily surface. It is prepared by infusing regular plywood with different chemicals under a certain pressure. These chemicals treatment makes this wood strong against rotting and mildew.

The main purpose of OSB plywood s is roof decking. It is manufactured with a water-proof glue and provides safety against excessive moisture. T1-11 is mostly used for sidings.

The best thing about this plywood is that it can be painted with natural color and can be well-matched against different color varieties.

  • If you have a limited budget use a CDX plywood. A Urethane coated CDX has very strong resistance against weather conditions.
  • While working with horizontal installations, pressure-treated plywood is a good choice. This wood lasts longer even in unfortunate drainage systems.
  • If you are working on a project that includes outdoor vessels for water flow, prefer marine-grade plywood. This type of wood is expensive but strongly resists moisture. It is perfect to use it for underwater applications like boats.
  • If you are working on any siding project, choose a T1-11. This type of wood is also good for big exterior wooden boxed. It can be easily stained for any desired color and appearance.


Now you have become familiar with our guide on how to seal plywood for outdoor use. Always select suitable plywood for your exterior project and then seal it step by step. The above techniques are used by professional woodworkers to extend an exterior plywood life.

Above mentioned methods and tips are also valuable for protecting edges of the wood. Sealing edges of the wood are significantly important because they are more exposed to weather conditions. If you seal plywood flawlessly, it will enhance your wood resistance capacity.

We are sure that you have got complete knowledge of sealing plywood and will be able to seal your wood like a pro!

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