Oriented strand board, or OSB, is a functional board, not a finish board. With its cross-hatched flakes of wood arranged perpendicular to each other, OSB does have many good features and it is widely used and accepted within the building and remodeling industry for qualities such as low cost, high strength, and easy availability. If you want to use OSB as a finish material, is it possible to paint it to make it more attractive and perhaps even improve its utility? Yes, you can paint OSB, but it is important to first understand OSB's many limitations regarding paint application.
Why Is OSB Difficult to Paint?
OSB stands for oriented strand board. Layers of chipped-up lower-grade wood (the strands) are arranged (or oriented) flat and perpendicular to each other. Cross-hatched strands impregnated by resins help create stability in OSB.
A relative newcomer to the world of wood products, OSB was never meant to be a finish surface. It is intended to be an underlying material for applications such as subflooring, wall sheathing, and roofs. But OSB sometimes does become a finish surface in places like sheds, laundry rooms, mudrooms, and basements.
The Engineered Wood Association (known as APA) notes that Exposure 1 OSB can be painted. The APA's main reservation is that OSB shipped with a thin wax coating would inhibit painting. The APA also notes that, due to the prominently visible nature of OSB's strands, it will show through on one coat of paint. A heavy primer may be required. They also recommend that you avoid exposing any of OSB's edges to moisture, as this may allow the OSB to swell and crack.
OSB is designed to hold up during initial periods of unintended exposure. OSB manufacturers do not recommend permanent exposure to the elements. OSB was designed as a way for remodelers and new home builders to deal with the occasional problem of building delays.
This is accomplished with resins and waxes that help OSB initially stand up against moisture, so that a partially completed home will not immediately disintegrate during those building delays. OSB rated as "Exposure 1" is very good at high moisture over long periods of time. But OSB does not last forever against moisture. If building is delayed long enough, water eventually penetrates the material and will cause it to swell and disintegrate. Edges cut on site are especially vulnerable to moisture penetration. Factory edges hold up better against water.
Limitations When Painting OSB
- While the color will be solid and complete with enough coats, the texture will always remain visible. You cannot achieve a smooth surface on OSB. Because OSB does not sand down smoothly, you will not be able to bring down the texture with sanding after painting.
- OSB often ships with a thin coating of wax which first needs to be stripped before painting. Some OSB only appears to have a wax surface coating, a result of the high pressure exerted on the material by the manufacturing machines.
- OSB's open strands readily absorb paint, requiring two coats at a minimum but more likely three coats. Older OSB will be especially porous, requiring several coats of paint plus primer. Particularly old OSB that is beginning to fall apart cannot be painted; the paint will not help glue the OSB together.
- OSB's cut edges are susceptible to water infiltration. Its factory edges are initially treated with a sealant. This sealant is not intended to last for long periods of time.
- Working Time: 60 minutes for 32 square feet
- Total Time: 1 to 2 days
- Skill Level: Beginner
- Material Cost: $20 to $50
What You Will Need
- Roller frame, 9-inch
- Thick nap roller cover, 9-inch
- Five-gallon bucket and screen
- Latex or nitrile gloves
- 80-grit sandpaper
- Orbital sander
- Shop vacuum
Lightly Sand the Surface
With 80-grit sandpaper fitted on the orbital sander, lightly sand the surface of the OSB.
Clean the Surface
Thoroughly clean the surface of the OSB. Due to the OSB's rough texture, tack cloth and cotton rags do not work well. Instead, clean the surface with a shop vacuum and brush attachment.
Prime the OSB
Pour primer into a 5-gallon bucket fitted with a screen. Slide a thick nap roller cover on the roller frame. Dab the roller in the primer and thoroughly roll it out on the screen. Prime the OSB by making W-shaped sweeps of the board. Do not apply too thickly. After at least two hours of drying time, apply a second coat of primer.
Paint the OSB
After the primer coat has dried, apply the paint. As with the primer, do not apply in thick coats. Rather, apply two to three light coats.
Tips for Painting OSB
- Prime with two coats of an oil-based primer such as Kilz Complete or Sherwin-Williams ProBlock.
- Roll on the primer and paint rather than spraying the paint.
- Leave as many panels uncut as possible to preserve the factory edges.
- For exterior applications, if you are not painting the OSB directly after installing it, be aware of how long you have before the material begins to be affected by the elements. For example, Weyerhaeuser Edge Gold OSB panels are warranted for 200 days against edge swell caused by water absorption.