OSB, or oriented strand board, has a flaked appearance and bumpy texture. It's a solid and popular choice for an underlayer for carpeting, tile, hardwood flooring, wall sheathing, and roofs. OSB is made of many layers of chipped-up lower-grade wood; these are the strands. These strands are arranged flat and then oriented perpendicular to each other. Cross-hatched strands impregnated with resins help create stability in OSB. Oriented strand board is primarily intended to be a functional board, not a finished board. It is widely used and accepted within the building and remodeling industry for its low cost, high strength, and availability. It is sometimes used as a finished surface in utility areas like sheds, laundry rooms, mudrooms, and basements.
If you want to use OSB as a finish material, you can successfully paint it to make it more attractive and perhaps even improve its utility. But OSB has a few limitations and requires special preparation before you start rolling on the paint.
The Engineered Wood Association (known as the APA) acknowledges that you can successfully paint "Exposure 1" OSB. Still, their central reservation is that OSB has a thin wax coating that protects it against moisture and inhibits painting. Also, OSB's strands' prominently visible nature will likely show through on one coat of paint, so filler and heavy primer are probably required to remove some of the texture of the wood. Also, you must avoid exposing any of OSB's edges to water, as it may cause the OSB to swell or crack.
OSB is designed to hold up to some initial periods of unintended rain or weather exposure, but OSB manufacturers do not recommend permanent exposure to the elements. OSB rated as "Exposure 1" is very good at handling high moisture over time but has its limit. If a building project 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 because they are finished with a sealant during manufacturing.
Before painting, you will need to do several things. Suppose you want to smooth out the texture so that the crosshatched wood chips are not visible. In that case, you can add a polyester resin filler such as 3M Platinum Plus Filler and repeatedly alternate filler coats with sanding to smooth out the board's texture.
Check with the manufacturer if the OSB has a thin wax coating to protect it. If it does, it will need to removed by using a wood floor wax stripper before you attempt to paint it. Some OSB only appears to have a wax surface coating, a result of the high pressure exerted on the material by the manufacturing machines.
Once your board is ready, be generous with the primer. OSB's open strands readily absorb the paint, requiring two or three coats of primer to close up the pores. Older OSB will be incredibly 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.
Whenever you plan to sand or paint, make sure you use a dust mask to protect yourself against the swirling particulate matter and the fumes of the harsh chemicals. Ventilate the room well with open windows and, if possible, use a box fan turned outward to pull out the paint odor from the room.
Equipment / Tools
- 1 9-inch Roller frame
- 1 9-inch Thick nap roller cover
- 1 5-gallon Bucket and screen or paint tray
- 1 Putty knife (optional)
- Latex or nitrile gloves
- Dust mask
- Orbital sander
- Shop vacuum
- Box fan
- 80-grit Sandpaper
- Polyester resin filler (optional)
- 220-grit Sandpaper (optional)
- Wood floor wax stripper (optional)
Lightly Sand the Surface
With 80-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
Don gloves. 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 resin filler coat with a putty knife. Apply it as thinly as possible. After the resin has dried (about 20 to 30 minutes), sand down the board and the edges with 220-grit sandpaper. You may need to repeat this cycle four or five times before all of the texture has been smoothed over.
Prime the Filler (Optional)
If you applied filler and have gotten it smooth to your satisfaction, you will need to 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. Instead, apply two to three light coats, letting each coat thoroughly dry before proceeding to the next coat.
Rolling vs. Spraying Paint
Roll on the primer and paint rather than spraying the paint. Most beginning DIYers have the most success when using a thicker layer of paint to fill the textured crevices of OSB. Rolling paint takes longer than spraying, but the coverage will be more consistent if this is your first time painting walls. If you decide to spray the first coat and have an uneven result, no worries, you can "backroll" or do the next layer using a roller and compare your satisfaction with the methods.
Seal the Edges
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. OSB's cut edges are susceptible to water infiltration. Its factory edges are initially treated with a sealant; however, this sealant is not intended to last for long periods. If you want to smooth out the edges, use the same method for applying the filler in Step 4 (above): Use a resin filler, then sand.
For use outside, if you are not painting the OSB directly after installing it, find out from the manufacturer how long you have before the material begins to be affected by the elements. For example, Weyerhaeuser Edge Gold OSB panels are warranted 200 days against edge swell caused by water absorption.
Finishing Exposure 1 OSB Sheathing. APA The Engineered Wood Association.
Steps to Lead-Safe Renovation, Repair, and Painting. United States Environmental Protection Agency.