Is OSB Waterproof By Default (6 Easy Steps)

OSB (oriented strand board) is a type of engineered wood product that is composed of layers of wood strands or flakes. OSB has become increasingly popular for use in building projects, due to its affordability and strength.

However, when considering using OSB for construction projects, it’s important to understand whether or not the material is waterproof by default.

Is OSB Waterproof By Default?

No, OSB is not waterproof by default. However, it can be treated to make it more resistant to water damage.

Many types of waterproofing treatments are available, so it is essential to consult with a professional before choosing one.

Depending on the intended use of the OSB, there may be other factors to consider as well, such as fire resistance or termite resistance.

OSB, or oriented strand board, is an engineered wood product. It’s made by compressing and bonding wood strands into a solid panel. OSB is often used as an alternative to plywood in construction projects.

If you are using OSB in an area where it will be exposed to water, it is essential to take steps to make it waterproof. Otherwise, the OSB could swell and warp, causing damage to your home.

How To Waterproof OSB

If you want to protect your OSB from moisture, you’ll need to waterproof it. Here’s a step-by-step guide on how to do just that:

Gather Your Materials

To start, you’ll need the following materials: exterior grade primer, exterior grade paint, a roller or brush, and something to catch any drips (like a tarp or drop cloth).

Prepare The Area

Before you start painting, you’ll need to ensure the area is well-ventilated and free of debris. Once the area is prepped, open up your OSB and set it on something level so you can easily paint all sides.

Prepare The OSB

Now it’s time to prepare the OSB for painting. First, use a brush or roller to apply a generous amount of primer to all sides of the OSB. Then, let the primer dry completely before moving on to the next step.

Paint The Faces

Once the primer is dry, it’s time to start painting the faces of the OSB. Again, use a brush or roller to apply an even coat of exterior-grade paint to all sides. As you paint, catch any drips with a tarp or drop cloth.

Paint The Edges

After the faces are painted, it’s time to move on to the edges. Like with the faces, use a brush or roller to apply an even coat of exterior-grade paint to all sides. Be sure to catch any drips.


Once you’ve finished painting, it’s time to test your work. First, check that the paint is dry by touch. If it’s still tacky, give it more time to dry. Once the paint is dry, pour a cup of water onto the surface and see if it beads or soaks in.

If the water beads up, your OSB is now waterproof. If it soaks in, you’ll need to add another coat of paint. Let the paint dry completely between coats.

Once your OSB is waterproof, you can use it for any number of outdoor projects. Get creative and put it to good use.

How Long Can OSB Be Exposed To Rain?

On average, OSB can be exposed to rain for up to 24 hours without significant damage. However, extended exposure to rain and moisture can cause the boards to warp and swell.

If you need to replace any damaged OSB boards, be sure to do so as soon as possible to avoid further damage to your home.

The lifespan of OSB exposed to rain will depend on several factors, including the type of OSB, the quality of the OSB, the climate, and more.

In general, however, you can expect OSB to last for several years when exposed to rain. With that said, it is always best to avoid caution and take steps to protect your OSB from the rain, if possible.

One way to extend the life of OSB exposed to rain is to finish it with a waterproof sealant. This will help to protect the OSB from moisture damage.

Additionally, it is essential to ensure that the OSB is correctly installed so that water cannot get in through cracks or gaps.

Finally, if you live in an area with a lot of rain, it is a good idea to check on the OSB periodically to ensure it is still in good condition. If you notice any damage, be sure to take action to repair or replace the OSB as soon as possible.

Will Painting OSB Make It Waterproof?

No; painting OSB will not make it waterproof. However, there are some things you can do to help protect your OSB from water damage.

Some people recommend using a water-resistant sealer on OSB before painting it. This will help to create a barrier between the OSB and the water, but it is not a guarantee that the OSB will not get damaged.

Another option is to use waterproofing paint on your OSB. This type of paint is designed to create a waterproof barrier on the surface of the OSB.

However, it is essential to note that this paint will not stop water from seeping through the OSB if there are cracks or gaps in the surface.

If you are concerned about water damage to your OSB, we recommend using a water-resistant sealer and waterproofing paint. This will help to create a strong barrier against water damage.

Can You Seal OSB For Outdoor Use?

Yes, you can seal OSB for outdoor use. There are a few different ways to do this, but using a clear polyurethane sealer is the most common.

This will help protect the OSB from moisture and weather damage. You can also paint OSB, but it is not necessary if you are going to seal it.

Do I Need To Waterproof OSB?

Waterproofing your OSB is essential if you live in an area with a lot of rain or snow. It will help to keep your OSB from getting damaged by the elements.

There are a few different ways that you can waterproof your OSB. You can use a sealant, paint, or even a tarp. Sealants are the most popular option because they are easy to apply and provide good protection.

Paint is also a popular option, but it can be more challenging to apply evenly. Tarps are the least popular option because they can be difficult to put on and take off.

Whichever option you choose, make sure that you follow the instructions carefully so that you can get the best results.

Is OSB Ruined If It Gets Wet?

No, OSB is not ruined if it gets wet. However, it is essential to dry it out as soon as possible to prevent the growth of mold and mildew.

If you’ve got wet OSB, there’s no need to panic. The material is engineered to be water resistant, not waterproof.

That means it will eventually succumb to moisture if left exposed long enough. However, as long as you take action to dry it out quickly, the OSB should be just fine.

If your OSB has been exposed to water, you first need to assess the damage. If the panels are only slightly damp, you may be able to dry them on your own. However, if they’re saturated or if there’s visible mold or mildew growth, it’s best to call in a professional.

Once you’ve determined that the OSB is salvageable, the next step is to take action to dry it out. If the panels are only slightly damp, you can try setting up some fans to circulate air and speed up the drying process.

However, if they’re saturated, you’ll need to remove them from the structure and place them in a well-ventilated area to dry completely. This could take several days, so be patient.

What Do You Cover OSB Board With?

You can cover the OSB board in a couple of different ways.

One way is to use a layer of Tyvek or another type of breathable house wrap. This will protect the OSB from water damage and allow it to “breathe.”

Another way to cover the OSB board is to use a layer of felt paper. This will also protect the OSB from water damage but won’t allow the board to “breathe.”

Whichever way you choose to cover your OSB board, ensure that you do it properly to prevent any damage to the board.