How to Paint on Greenboard

Sand down any rough surfaces on the greenboard, with medium-grit sandpaper. Greenboard is texturized, like drywall, so the smoother the surface, the better the paint will go on and appear once it's dry. If you don't have a lot of surface area to cover, you can use sandpaper blocks by hand. If you have a large surface area or green wall to cover, use an electric sander to help you accomplish the sanding process faster.

Paint a coat of latex-based primer onto the greenboard using a 4-inch wide flatting paintbrush. Latex primers are effective for use on drywall because of their ability to maintain a smooth surface. If you use an oil-based primer, the primer will raise the texture of the greenboard -- making the surface look uneven and unfinished.

Let the primer dry for the amount of time specified on the product's label. You may need to wait one or two days after your coat of primer to apply the paint. Touch the primer to see whether it still feels tacky after one or two days.

Pour the finish paint into a 5-gallon bucket. You can also use a paint tray, but these can tip over if you accidentally step on them. A bucket maintains the paint more effectively from such accidents.

Dip the paint roller into the paint, and roll it over the coat of primer. Apply one coat, and see how the wall looks after it dries. You can add a second or third coat, but let each coat dry first before adding another on top of it. Drying time for paint may be up to 24 hours, but may be less if you purchase a fast-drying paint. Consult the paint's label for the recommended drying time.