Shiplap Walls Using Plywood- 5 Reasons to Use Exterior CDX Plywood Instead of Luan Underlayment

Before I share our post on how we installed shiplap walls using plywood in our bathroom, I wanted to go over the reasons why we chose exterior plywood instead of luan (aka underlayment). After using this type of plywood, I’ll never go back to luan!

If you’re a fan of Fixer Upper, then there’s a 75% chance you’re also a fan of shiplap walls.

I know this girl is.

Very few of us are blessed enough to find authentic shiplap under our existing wall surfaces like you see on the show. And not all of us can afford to buy actual shiplap (the kind that has a special notch cut on the edges of the board)…that’s if you can even find it in stock at your local home improvement store.

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Most DIY shiplap tutorials I’ve seen use 4’ X 8’ sheets of 1/4″ luan underlayment ripped down to 6” to 8” wide planks. We’ve used 1/4″ underlayment as faux shiplap before and were happy with the results.

Regardless, we knew we wanted to use 3/8″ exterior plywood, also known as CDX plywood, instead of luan underlayment when we were ready to plank our bathroom walls.

So, what made us choose to use exterior grade plywood to shiplap our master bathroom instead luan underlayment (or even authentic shiplap)?

Here are 5 reasons:

1. Texture

The reason we’ll go back to using exterior plywood to shiplap walls in our house time and time again is that it has so much more texture than the luan which makes it look more like the real thing. You can see in the comparison photo above the difference in the wood grain but it’s even more noticeable in person. We used a satin finish paint for our bathroom walls but a semi-gloss would show off the texture even more.

2. Humidity Resistance

The “X” in CDX means the plywood can withstand exposure to the elements over a short period of time before it’s painted or sealed. The main difference is that they use an exterior-grade resin glue to hold the layers of the wood together. Since we’re “shiplapping” our bathroom, we wanted something that would withstand the humidity and be less likely to delaminate over time. After putting the boards up, we covered the planks with primer before we painted. Speaking of humidity, it’s important that you have an adequate exhaust fan. We used this calculator to see what size fan we needed and ended up ordering this one.

3. Cost

The cost difference between exterior plywood and luan underlayment was only a couple dollars per sheet…$13 for luan and $15 for plywood. Either way, you go, it’s inexpensive. When you figure the cost of real planking at $2.20 per square foot, using exterior plywood at $0.47 per square foot will win my vote every time.

4. Durability

The 3/8″ exterior plywood is less likely to warp over time compared to 1/4″ luan. It’s also less likely to split when cut or nailed.

5. Thickness

The thicker the plywood, the more noticeable depth the gap is between the planks. This makes the faux planks feel more authentic. Also, having 3/8″ thickness of wood compared to 1/4″ gives more wood for the nails to hold onto. But, you can also run into problems if you go too thick. Actual shiplap planks are usually an inch thick which means you’ll have to take off the window and door trim. The 3/8″ thickness is a good compromise although we did had to remove the trim below the window sill because the profile would’ve been hidden.

There are some drawbacks to having shiplap walls using plywood that you need to consider too:

Exterior plywood needs a little bit more prep work. Even though it comes pre-sanded, the surface of the CDX plywood is what I would call “hairy”. The fibers tend to stick up a little bit. Fortunately, sanding gets rid of the hairiness.

Also, you run into the occasional problem with having knots on the surface. The knots can be filled with wood filler and then sanded. Spot prime over the knots with B-I-N Zinsser shellac primer to seal the knots and prevent the from sap bleeding through the paint. Then, use an all-purpose interior/exterior primer for the rest of the walls before you paint.

I can’t imagine this bathroom without the shiplap. I’ll be posting a tutorial on how we shiplapped our walls this coming week. It’s easier than you think!

* Update: Here’s our tutorial and tips post on faux shiplap

If you have any questions about how to shiplap walls using plywood, please feel free to leave a comment. If we don’t know the answer, we’ll research it for you.

We also used exterior plywood to plank the walls and ceiling in our cottage shed guest house. Click here to see the reveal of our guest house or click the picture below.