Oriented Strand Board (OSB) is an excellent alternative to plywood. OSB is thicker than plywood, making it more robust. You can use it for flooring, roof sheathing, wall sheathing, or even building furniture. OSB is manufactured by blending resin with young wood strands. This process makes the board exceptionally tough. Manufacturers waterproof the boards before sale. However, before crafting furniture or other items, you may still need to waterproof it for extra moisture protection and durability. This is especially crucial for OSB's outdoor applications. Here we'll discuss how to waterproof OSB.

Key Steps for Waterproofing OSB

You can easily waterproof OSB. When purchasing oriented strand board, ensure the back is labeled “waterproof.” This will simplify your additional waterproofing task. Here are the steps you should follow:

Plan ahead before cutting. When you cut the edges with a sealer, it wears off and creates new openings. Moisture can then be absorbed through these areas. Therefore, cut the OSB into pieces before waterproofing to prevent water from becoming trapped inside. Store the cut pieces in a secure location away from soil or grass that could block them.

If you want to enhance waterproofing, you can paint the OSB. If you decide to paint it, this must be done before waterproofing so the paint won't get damp or affected by water. You can use oil-based or latex-based paint.

Then you should apply the waterproofing. You can purchase a quality waterproofing solution from your local hardware store. Make sure the waterproofing solution you buy is suitable for wood. You only need to use a brush to apply the waterproof coating to the OSB pieces. Repeat the application on each side. The waterproofing layer takes approximately 12 to 14 hours to dry.

To verify the OSB is waterproof, pour some water onto the OSB sheet and wait several hours. If the water does not soak through, the OSB sheet is now waterproof.

Differences in OSB Use for Interior vs. Exterior Applications

OSB can be used for exterior applications. However, these OSB panels are classified as Type 3, making them suitable for use in humid conditions. Even if you purchase waterproof OSB from the market, you should apply an additional layer of waterproofing material to protect the board from moisture or water exposure. OSB intended for interior use contains phenolic or diphenylmethane diisocyanate (MDI) adhesives to prevent health hazards. After purchasing waterproof OSB panels, no further waterproofing treatment is required.

OSB is more water-resistant than plywood. Therefore, OSB can be used for both indoor and outdoor projects. Ensure you know how to waterproof OSB panels to add a moisture-resistant or waterproof barrier.