When confronted with OSB board, with its flaked appearance and bumpy texture, many do-it-yourselfers and crafters want to paint it.
The issue is that oriented strand board is a functional board, not a finish board. With its cross-hatched flakes of wood arranged perpendicular to each other, OSB does have many superior features. 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, it is possible to paint it to make it more attractive and perhaps even improve its utility. In fact, you can do so quite successfully. But it does require special preparation, plus it is important to understand OSB's nature—before you start rolling on the paint.
What Makes OSB Difficult to Paint?
OSB is made of many layers of chipped-up lower-grade wood; these are the strands. These strands are arranged flat and then perpendicular to each other; that's the orientation. Cross-hatched strands impregnated with resins help create stability in OSB.
A relative newcomer to the world of wood products, OSB was never meant to be a finish surface. OSB 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.
Keep In Mind When Painting OSB
- Texture: 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. The way to fix this is with filler.
- Filler: Adding a polyester resin filler such as 3M Platinum Plus Filler and repeatedly alternating coats of filler with sanding will smooth out OSB's texture.
- Wax Coating: 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.
- Large Quantities Needed: OSB's open strands readily absorb the paint, requiring two or three coats of primer just to close up the pores. 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.
- Sealing the Edges: 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. If you want to smooth out the edges, use the same method as detailed above: using resin filler, then sanding.
- 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
- Putty knife
- Latex or nitrile gloves
- Dust mask
- 80-grit sandpaper
- Orbital sander
- Shop vacuum
- OSB board
- Polyester resin filler
Lightly Sand the Surface
With 220-grit sandpaper fitted on the orbital sander, lightly sand the surface of the OSB. Do not sand the edges.
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 Multiple Times
Pour primer into a tray. Dab the roller in the primer and thoroughly roll it out on the tray. 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. Repeat this process until the OSB's flake pattern no longer shows through.
Apply the Filler (Optional)
If you want to smooth down the surface and edges, apply a coat of resin filler with the putty knife. Apply as thinly as possible. After the resin has dried (about 20 to 30 minutes), sand down the board and the edges. You may need to repeat this cycle four or five times before all of the texture has been smoothed over.
Prime the Filler
Once the OSB is smooth enough to your satisfaction, prime it twice.
Paint the OSB
After the last primer coat has dried, apply the paint. As with the primer, do not apply in thick coats. Rather, apply two to three light coats, letting each coat thoroughly dry before proceeding to the next coat.
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. While factory edges are not perfectly smooth, they are still smoother than edges cut with a circular saw.
- 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.
Engineered Wood Construction Guide. The Engineered Wood Association