Oriented strand board, or OSB, is rarely considered attractive enough to be a finish material. With its cross-hatched flakes of wood arranged perpendicular to each other, OSB looks like water-logged cardboard. Yet OSB does have good qualities 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 even improve its functionality?
OSB and Paint: Limitations and Expectations
Yes, OSB can be painted. However, be aware of the limitations associated with painting this material and expect the following:
- Texture Will Be Visible: 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.
- Priming Will Be Required: While priming may be optional with some surfaces, it is absolutely necessary to apply primer before painting OSB.
- Wax Coating May Need to Be Removed: Some OSB 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.
- Extra Coats May Be Needed: The 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.
- Edges Are Especially Porous: 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.
While Not Beautiful, OSB Is Highly Functional
Within the world of wood, OSB is a relative newcomer. Georgia Pacific, a major supplier of wood products, has offered OSB only since 1980.
OSB stands for oriented strand board. Literally, this means that layers of chipped-up wood (the strands) are laid perpendicular (or oriented) to each other. It is this cross-hatching that helps create stability in OSB.
OSB is not meant to be a finish surface. It is intended to be an undersurface material for applications such as subflooring, wall sheathing, and roofs. But it sometimes does become a finish surface in places like sheds, laundry rooms, mudrooms, and basements.
OSB and Moisture
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.
Resins and waxes help OSB initially stand up against moisture, so the 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.
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.
- Seal cut edges of the OSB with multiple coats of primer.
- 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.
What Is the Official Word?
The Engineered Wood Association (known as APA) is the non-profit trade association that represents manufacturers of OSB and other engineered wood products. The 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 probably 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.