Does Plywood Rot? Plus How to Fix it!

Plywood is used in all sorts of building applications, including roofing, flooring, siding, and even for specific marine uses. If you’re not all that acquainted with the ins and outs of plywood – few of us are – then you might be wondering whether or not plywood rots or not.

The short answer is that, yes plywood can and will rot if it becomes exposed to moisture and the elements for too long. The long answer is a little more complex, as the amount of rot depends heavily on the type of plywood you’re working with, as well as how much moisture it’s been exposed to.

Let’s take a closer look at the ins and outs of plywood rot, how you can prevent it from happening in the first place, and what you can do when you do discover plywood rot.

What Causes Plywood Rot?

Like any other wood rot, the key ingredients to plywood rot are prolonged moisture exposure and lack of a protective coating. Typical situations where you’ll find plywood rotting are in a leaky roof underneath the shingles or a subfloor with leaky plumbing.

Plywood is made from multiple thin layers of wood called veneers, which are sandwiched together and then bonded with a resin to form a strong composite material.

When moisture is allowed to soak into the plywood – particularly at its edges – it’s susceptible to rotting. The edges are particularly vulnerable to rot, as they are exposed to the elements – and water is able to wick up into the edges much easier

What does Plywood Rot Look Like?

Plywood rot looks similar to other wood rot. It’s crumbly, weak, and will fall apart without any real resistance. If it’s covered in paint, the paint may appear chipped and flaky.

You may also notice a damp, musty smell, shrinkage, and fungus growth in the rotted area.

You can test if plywood is rotten by poking it with the edge of a paint scraper or screwdriver. If you can push right through the material without any resistance, then it’s rotten and will need to be repaired or placed.

How Long does it Take Plywood to rot?

This one really depends on the grade of plywood you’re dealing with. Cheap low-grade plywood that isn’t rated to handle moisture will obviously disintegrate faster than plywood designed to hold moisture or marine-grade plywood.

A word on plywood types:
There is actually a lot to discuss when it comes to the different grades of plywood. There are slightly different grading systems for softwood and hardwood plywood.

For softwood, A-grade is the highest level, and is smooth and flawless, making it appropriate for surfaces where it will be exposed. B-grade is less smooth and will have some flaws. C-grade will have even more flaws, up to 1.5-inch in diameter. And finally, D-grade plywood is the cheapest and will feature large flaws and imperfections.

Hardwood also has a rating system between 1 and 4 for the “back” veneer, which is important for when both sides of the plywood will be visible. Plywood ratings with the letter “X” at the end of them refer to “exposure” – which means they’re capable of handling a small amount of moisture, but not for a prolonged period.

So, for instance, BCX grade plywood would indicate the face veneer is B-grade, the back veneer is C-grade, and its rated to handle outdoor exposure.

Lastly, marine-grade plywood is the most moisture-resistant type you can get your hands on. It’s rated A-A, A-B, or B-B, which indicates the quality of the front and back sides. For instance, A-B would indicate a perfectly smooth and flawless front side and a slightly flawed back side.

How do you fix plywood rot?

So, what do you do if you actually run across some plywood rot while working on a project around the house?

First of all, you’ll need to assess the level of damage. If you have easy access to the plywood, then you’ll want to poke and prod it with a sharp object all along the edge and test the extent of the rot.

There are several different epoxy products you can use in the case of plywood rot, each with its own specific use case. Epoxy consolidants are ideal for situations where the wood has lost some strength but still retains its basic shape. This is typically the case when you’re talking about wood rot or even insect damage.

The second product is epoxy paste fillers, which are designed for situations where some of the original fiber has been lost, and you need to replace it. If you have large holes or gaps in your plywood piece, then you’ll need to use a product like this to essentially replace the missing material.

How to Prevent Plywood Rot in the First Place?

If you want to prevent the above situation from happening in the first place – then you’re in luck! There are a number of products you can use to create a protective coating that will prevent any wood rot from starting.


A simple paint job will provide a fairly solid level of protection for typical plywood, and is enough for plywood that only has occasional exposure to moisture. It’s a good idea to apply a layer of primer before painting, as this further increases the protective layer, and helps the paint to bond with the plywood surface.

Epoxy Sealant

If you want the highest level of moisture protection, then an epoxy sealant is the way to go. This will give you a near impervious protective layer over your plywood.

Epoxy sealant is usually clear, so the plywood will retain its original appearance.

Drying Oils

Drying oils are oils that harden to a tough, solid film when they’ve been allowed to cure. They aren’t entirely waterproof though, so won’t give you the same level of protection as an epoxy sealant will.

Some examples of drying oils are linseed oil, tung oil, and teak oil. These oils tend to take a fairly long period of time to fully dry and cure, so they may not be appropriate for situations where time is a major constraint.

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Denis Gardner

I've loved tinkering and fixing things for as long as I can remember. So, naturally, I gravitated towards DIY and home improvement when I bought my first home. Nowadays you can find me writing about my passions or messing around with my newest tool!

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