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 look good 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 the 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 outdoor 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 You Begin
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 be 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.
Source: The Spruce