How to Protect OSB from Rain

If you need to utilise Oriented Strand Board (OSB) to sheathe your shed’s walls, then you would need to construct those walls like the walls of a house. This means you would need to use a moisture-resistant barrier over the OSB and then cover it with siding. Vinyl siding is recommended because it is inexpensive and DIY-friendly.

What Is OSB?
OSB is an engineered wood product made from compressed layers of wood strands bonded with adhesives (usually synthetic resin and wax). This wood product has existed since 1963, and as opposed to its counterparts, the strips of wood in every layer are applied strategically rather than randomly to enhance its strength. Each panel can consist of up to 50 layers of wood.

How to Protect OSB from Water?
Some people opt for OSB as an alternative, while others use it as a replacement for plywood. Whatever way you take it, OSB is usually waterproofed during the manufacturing process. However, if you intend to use it for an exterior application, you may need to make it more resistant to water by adding a protective layer. We compiled this info on how to protect OSB from rain.

Step 1: Ensure Your OSB Is Waterproofed
Check whether your OSB has that ‘waterproofed’ stamp on its surface. All OSB are waterproofed to some extent, but knowing to what point will help you.

Step 2: Plan and Cut Pieces
Whenever you cut your OSB, you will interfere with the edges, and any sealer will be lost, leaving spaces for water to enter. As such, you should cut beforehand the pieces you need before adding waterproofing to protect the edges. Measure, mark, and then cut the desired dimensions and set them aside.

Step 3: Paint If Necessary
Exterior paint will not only make your OSB attractive, but it also adds a layer of water resistance. So, the paint should be added before applying the waterproof so that the sealer can protect the topcoat.

Note: if you need a more natural appearance, you can stain your OSB.

Step 4: Apply Waterproofing
You can buy a high-quality sealer from your home improvement store or local hardware. To apply, soak the tip of the paintbrush in the sealer and brush it over the OSB board’s ends and surface. Ensure this process is repeated on both sides, and not just the areas where you made cuts. Coat your OSB pieces and allow the seal to dry for 12 to 14 hours.

Now turn the wood and coat the remaining surfaces. If you need more layers of waterproofing for more protection, you can add them. Just allow each layer to dry for 12-14 hours before adding the next layer.

Step 5: Test
The last step on how to protect OSB from water is testing to ensure you applied enough waterproofing on your OSB. To test, pour some water on your waterproofed piece and allow it to sit on the surface for some hours. If it doesn’t soak the board after those hours, chances are your OSB is well waterproofed. If not, you would need to add more layers and allow it to dry before testing again.

Can OSB Board Be Used Outside?
Engineered wood sheet materials are described and categorised by DIN EN 13986. To be used for exterior applications, OSB should be classified as class 3, so OSB/3 and OSB/4 are ideal for use in humid conditions.

Can You Seal OSB?
Yes. There are several OSB sealers you can use to protect your OSB against moisture and water. Most of these sealers are odourless during application and once cured.