Plywood is flammable and as such is not a recommended material for walls. In cases where it already exists or its use is inevitable, you can smooth the textured surface with joint compound and paint it after priming with a high-hiding primer. It is advisable to trim the edges rather than try to tape or fill them because the plywood will move, and the tape joint or filler will inevitably crack. If a clear finish is desired on veneered plywood, spray it on with an airless sprayer after priming with a clear wood sealer.
Mask off the area around the wall with masking tape and paper. Cover shrubs, furniture or other immovable objects you don't want to paint with plastic dust sheets.
Apply a coat of drywall joint compound to the entire wall if you plan to paint it with coloured paint. Let it dry, sand it, and repeat with a second coat.
Fill the cup of an airless spray gun with primer. Test the spray to make sure that the mixture flows smoothly, and thin it if the spray is chunky or uneven. Rotate and tighten or loosen the nozzle to get a vertical spray pattern that is about 12 inches wide from a distance of about a foot.
Spray the wall with primer or clear sealer in a continuous left-right pattern from top to bottom, overlapping about half the width of the pattern on each pass. The goal is to get full coverage without drips or runs. If you can't get both, it is better to spray again than to have to clean up drips. When you are finished, turn the nozzle 90 degrees, and spray in an up-down pattern from left to right. When the primer has dried, sand lightly with 150-grit sandpaper, and apply a second coat in the same way.
Sand the walls lightly with 150-grit sandpaper, and spray on paint or clear-coat, following the procedure in step 4. Spray on as many coats as it takes to get satisfactory results, sanding lightly between each coat.
Clean the gun throughly after each use. Wash the cup with solvent, and immerse the tip in solvent for 10 minutes to an hour, wiping it well afterwards with a clean rag. If the paint sags or drips, you may be holding the gun too closely or moving too slowly.
Airless sprayers use high pressure to force paint through the nozzle. This high pressure can force the paint through your skin, so keep hands away from the spray pattern at all times. Never point the gun at yourself or anyone else.