Can You Put Plywood Over Deck Boards? (Why You Shouldn't)

One of the solutions that are often bandied about on carpentry forums is whether or not it’s a good idea to lay plywood down over existing decking, especially if the existing wood wasn’t properly maintained prior, and the deck boards look awful.

You can certainly lay down plywood over your existing deck boards if you want to, however, the real problem is whether or not you should. There are a lot of potential problems with it so the short and simple answer is no, you shouldn’t.

The most obvious problem with laying plywood down over deck boards is that it’s a temporary solution to a bigger problem. If your deck boards look awful, the odds are that your joists, beams, and posts look even worse.

Problems with Laying Plywood Over Deck Boards

It’s all about quality and if you’re looking to fix something that’s broken about the existing deck, covering it up in one or two giant, plywood solutions aren’t going to make the problem go away. In fact, it will probably make it worse.

If the current deck is rotting away, there will be two, immediate problems with laying down plywood. Number one, the plywood will itself rot more quickly than it would have before.

Number two, You just added more weight to a structure that is quite possibly beginning or is well into the process of buckling under the current weight.

If your existing deck is new and strong, there’s really no reason to install plywood over the top, although it wouldn’t endanger the current decking or make a good situation bad.

What it would do is give you a wide, flat deck surface that is more prone to holding moisture from rain, snow, and high humidity. It will also increase the chances that moisture below the deck will get trapped, reducing the lifespan of the overall deck.

Of course, you could also go for something that you would consider an upgrade over existing deck boards, like waterproof vinyl decking.Econodeck offers such an option and it has a clean, aesthetically pleasing look and feel.

Replacing Your Existing Deck or Surface Boards

If you want to lay a plywood deck over your existing deck boards (perhaps you’ve stubbed your toe one too many times in the spaces between the boards), you should go with something that’s waterproof.

That means something along the lines of the above-suggest Econodeck Vinyl decking option. The reason that you need something waterproof is that by covering the existing deck boards, you eliminate the drainage aspect of the deck.

So, you’ll want to replace something that can drain, with something that can’t drain, yet is fully waterproof. So, when it comes to placing plywood over existing decking, it’s important that you get it right.

You essentially have 4 options with plywood and your existing deck.

Replace the existing deck partially or altogether
Use waterproof vinyl decking that you purchase “as-is”
Place plywood over the existing deck and waterproof the plywood
Clean and refurbish existing deck

Replacing the Existing Deck

Deciding to replace a bad deck can be a difficult choice because it’s going to involve a lot of work. One important first step is to look over what you have and determine how bad it really is.

For instance, if there is a lot of cosmetic or surface damage with the deck boards, you can remove a few of them and get a bird’s eye view of whether or not that damage extends to the beams, joists, or posts.

If it doesn’t you’re in luck and the biggest job you have to do is replace the deck boards. Whether or not you go with plywood is entirely up to you.

Waterproof Vinyl Decking

If everything is good with the underlying deck and the deck boards, you can certainly add some of your sense of style by going with the highly aesthetically pleasing option of vinyl deck boards.

Econodeck is the most predominant retailer of waterproof vinyl decking options and their selection is pretty fantastic. They’re not hard to install over the existing deck either, and you will find a ton of information on them by visiting the site and possibly, making a selection.

The best part about this choice is that there is very little that you have to do outside of purchasing the vinyl deck pieces yourself. They are already designed to be completely weatherproof and waterproof.

According to their site, “Econodeck was specifically designed and developed for DIYers.” They’re easy to install and you’ll have an entirely new-looking deck with an upgraded aesthetic for the least amount of effort.

Place Pressure-Treated Plywood Over the Existing Deck

This is the closest to the original question that you can go, simply placing plywood down over existing deck boards. Even pressure-treated, however, it should be cleaned, stained, and sealed just like any deck should.

Of course, with plywood, a few additional options are opened up, such as liquid rubber, if it suits you to make your deck look like a giant, concrete slab.

Liquid Rubber/Latex
Deep oil penetration
Paint
Epoxy stain

Painting plywood makes a lot more sense than painting deck boards because deck boards are installed with a bot of spacing in between, allowing the water to drain. Paint is the most complete option for waterproofing, even over staining, and your plywood certainly needs waterproofing.

Clean and Refurbish

This is your last option and it’s only an endeavor you should take if the effort is worth it. If your deck is simply ugly, not previously stained, and not rotting, it’s definitely salvageable.

So long as your structural pieces that are burdened with the weight of the entire deck are not damaged or compromised in any way, you can clean everything up, sand it down, stain it, and seal it to restore its original luster.

Final Thoughts

You can lay plywood over deck boards, however, there’s generally no reason to and you should have a reason for undertaking the effort.

If you think it’s worth it, now you know that you have a lot more in the way of options than just slapping some plywood down and hoping for the best.

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Can You Put Plywood Over Deck Boards? (Why You Shouldn’t)