Plywood, just like any other wood, requires preparation before painting. The quality of the preparation determines the finished quality of the painted surface. If you start with furniture or marine grade plywood, the preparation is easy — those types of plywood are very smooth. Less expensive plywood for use as flooring, roofing or sheathing materials on a house probably won’t turn out as well since it has a rough surface that will show through the paint.
Sand the plywood until it is smooth using your sanding block or a handheld oscillating tool with a sanding accessory. Start with 80-grit sandpaper on a rough surface to begin the process and move to the progressively finer grits of 120 and 220. On marine or furniture grade plywood, begin with 120 grit since they are already quite smooth.
Wipe the plywood clean with the dry rag to remove most of the dust created by sanding. Don’t dampen the rag; the water will raise the grain and you’ll have to sand again. Wipe it a second time with the tack cloth to remove the finer dust that remains.
Pour primer into the paint tray until the lower half is full. Roll the roller into the paint and back out to coat the roller with primer. Roll the primer onto the plywood in the direction of the grain, working in areas about 2 feet square. Continue until all the plywood is covered. Let the primer dry 24 hours.
Lightly sand the primer with 220-grit sandpaper. Don’t try to remove the primer, just smooth it. Wipe the primer with tack cloth to remove the dust.
Prime the plywood a second time in the same fashion as the first. Work in small areas, moving from one to the next and always working to keep the edge of the primer wet. Let the second coat of primer dry overnight. Lightly sand the primer with 220-grit sandpaper and wipe it clean with tack cloth.
Pour paint into the paint tray until the bottom portion of the tray is full. Wet the roller in the paint and apply it to the plywood, always rolling in the direction of the wood grain. Work in small areas, about 2 feet square. Apply the paint evenly. Let the paint dry overnight.
Sand the paint lightly with 220-grit sandpaper. Wipe it clean with tack cloth and apply a second, final coat of paint with the roller.