Do You Need to Seal Marine Plywood?

Image of Marine ply wood but, Do You Need to Seal Marine Plywood?Marine plywood is reputable due to its high tolerance to environmental elements, durability, and a lot more. This wood does not have chemical treatment, making it susceptible to the most damaging elements in the long run. So do you need to seal marine plywood?

Much as the Marine-Grade Plywood is strong, long-lasting, and resistant to moisture, it still requires that you add an extra seal on it to prevent moisture from damaging it.

Sealing your marine plywood is critical for its durability. Failure to protect it could lead to rotting as well as discoloration. As soon as you seal it, you can go further and add other finishes such as polyurethane.

What Is Marine-Grade Plywood?

According to APA, Marine-grade plywood is a special panel created using Douglas fir or Western Larch.

Marine-grade plywood, simply marine plywood, confuses a lot of people to think that it is waterproof. It is a good-quality, hardwood plywood that has waterproof glue; this wood is not treated using chemicals hence does not resist rot.

This wood exists in 4 grades, with the better grades being lightweight, strong, and comes with no forms of defects. It is these exceptional qualities that make marine plywood a popular choice when constructing boats and their parts. Additionally, this wood makes a perfect choice for those looking to make doors along the coastlines, but first, you need to give it a protective finish.

How to Seal Marine Plywood

Until this point, you at least know that Marine-Grade Plywood is strong, lasting, and above all, comes with some level of resistance against moisture; even so, it would be best if you seal it for extra protection. Here’s the process of sealing marine plywood:


  • Acetone
  • Sanding block
  • Paper towels
  • Foam roller
  • Sandpaper 
  • Paint basin
  • Foam brush
  • Sealer

Step One: Clean Surface Of Plywood

Dip a piece of cloth or rag into acetone and use it to clean the surface of your plywood board. Acetone, in this case, helps in getting rid of grease and other unwanted stains from your wood. After cleaning with acetone, allow it time to dry. It should take about an hour or two for the acetone to dry.

Image of Makita, one of the Best Belt Sander for WoodworkingStep Two: Sand Surface Of the Marine Grade Plywood

Fine-grit sandpaper is the best for sanding plywood. You can fix it on your wood sander and use it for several minutes to achieve the best results. Use a piece of cloth or a shop vac to eliminate sawdust particles from your wood. 

Step Three: Apply Sealant Using the Foam Roller

Have your selected sealer ready in a basin for the step. Here, it would be best if you dipped the foam roller into the wood sealer. If you want to avoid “picking” too much sealer, then roll the brush against the sides of the basin. I recommend that you roll the sealer you choose for this purpose onto a 2-by-2-foot area to ensure that the sealer does not dry too quickly. 

Even as you apply the formula, ensure that you are focusing on one section at a time until you cover the whole plywood with a thin coat. One way of eliminating brush marks from your sealer is by dragging a foam tipping brush over the sealer when it’s still wet. Make sure that you are painting horizontally and not vertically.

Step Four: Allow the Formula to Dry

After you have applied your formula, you must allow it to dry. Usually, it takes between one and two hours for the coat to dry. Once the surface dries, you can add more thin layers as you see fit for your project. At this stage, feel free to alternate between vertical and horizontal strokes. 

About four thin coats of the sealer should do the job and give you the best finish for your sealing project.

How Long Does Marine Grade Plywood Last?

Suppose you compare the Marine Grade Plywood and its traditional counterpart. In that case, you will find it far more durable, especially if you use the two in areas prone to water and moisture like exterior projects such as picnic tables. So, how long does marine grade plywood last?

The Marine grade plywood lasts between 10-25 years, depending on the quality and how you use the plywood. 

It would help if you had a proper understanding of some of the factors that influence the plywood’s durability so that you know exactly what to do to help prolong its service life.

Factors that Affects the Lifespan of Marine Grade Plywood

There’s a notable difference in the durability of marine-grade plywood, and the difference is dependent on many factors such as the quality of the plywood, the amount of moisture the plywood is exposed with overtime. Other factors include the chemicals used in the treatment of plywood. If you are looking to project the number of years your plywood can serve you, it would be best to account for all these factors.

If you are in the market for marine plywood, you need to understand various plywood grades and settle for the one that will make a perfect fit for your project in question- influenced by the use and area in which the project is based. With the right plywood, you can rest assured of the best Return on Investment (ROI) from your projects.

Here are some of the factor:

  • Quality Of Your Plywood

Plywood exists in up to four grades ranging from A-D. Grade A is the best quality of all four, while D is the lowest quality.

As you’d expect, the plywood with the highest quality stands for every chance of lasting longer than the rest. The wood is either A-grade or B-grade in marine-grade, with grade A lasting longer and better than grade-B.

As you choose your plywood for projects best known to you, you must get the right supplier. Marine-grade plywood undergoes a more extensive treatment process, which is why certified and best-reviewed lumber suppliers are the most reliable for producing waterproof plywood that is durable. 

Additionally, I encourage that you only make purchases of plywood from the suppliers you trust and have a reputation for providing high-quality and lasting wood

  • Moisture Levels in the Environment

Wood moisture moistureOne of the major reasons many people go for marine plywood is higher moisture resistance, especially when comparing it to traditional plywood. You can attribute the higher water-resistance of marine plywood to the fact that it has an added layer of protective chemicals that resists water and moisture to ensure the durability of up to decades much as it is exposed to a considerable amount of water and moisture.

Even though plywood has high moisture resistance, it is not permanently resistant as it gets affected by water in the long run. Plywood that sees more exposure to water will break down faster than the one used in areas that experience low levels of moisture.

Bottom line, a Marine grade plywood in water exposure areas, such as in dock construction, can last at least fifteen to twenty years. When the same plywood is used in home decks or interior flooring, it can last up to twenty-five years or more, especially if you accord it proper care.

NOTE: You can use a moisture meter to determine the moisture level in any wood including plywood.

  • Chemicals Used In the Treatment 

Image of ready seal, best stain for deckThe only sad thing about traditional plywood is that it does not have added layers of protective material. We all know that prolonged exposure of wood to water has damaging effects; it’s the same for traditional plywood. Considering that this wood does not have any chemical treatment, it can warp and rot due to water.

Marine-grade plywood is special because it is treated with chemicals. The chemicals play an important role in repelling water and, in turn, prevent moisture from getting into the wood cells to cause damage. It would be best if you offered the plywood further protection against moisture using wood sealers, especially those made specifically for marine plywood.


Different Grades of Plywood

A-grade plywood: It is the best quality plywood, making it the most expensive in the class. Its veneers are flawless, making it smooth and arguably the easiest to paint or other finishes.

B-grade plywood: The B-grade plywood is a bit less smooth than its A-grade counterpart; however, it has a solid foundation. This grade of plywood has some minor flaws, but you can repair them to achieve top quality.

C-grade plywood: As for this grade, you get a few knots in the sheets; usually, the knots have a diameter of up to 1.5 inches.

D-grade plywood: It is by far the cheapest type of plywood veneer. The sheets have not undergone repairs and have slightly larger flaws, with knots as large as up to 2.5 inches in diameter.


There are no words to describe how good marine plywoods are for projects in areas that see a lot of moisture, especially the maritime environments. With the right grade of plywood, your projects stand a chance against the test of time, delivering top performance in the process. Much as marine plywood is durable and can withstand moist conditions, it still has some shortcomings, especially due to prolonged exposure to water. Even as you use it for different purposes…

Do You Need to Seal Marine Plywood?

Yes, you need to seal your marine plywood. Much as it can resist moist conditions, it gets overwhelmed with time and will start breaking down. Select the right sealers and enhance the durability of your marine plywood.

The natural durability of marine plywood coupled with enhanced protection against elements such as water and UV rays will ensure that your structure can last up to 2 decades or more, is a coastline environment.

I hope you have read this post and gotten insightful information on whether or not you should seal your marine plywood. If you have questions, additions, or any form of suggestion that will make this content better, kindly share it with me in the comment section below.

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Tyron Otieno

Tyron is an avid woodworker and writer. He founded this website to help other woodworkers, whether hobbyists or professionals by sharing his knowledge and experiencie after a decade of woodworking.