Wipe down orange-peel walls with a damp sponge to ensure no dust or grime is on the walls. Paint will not stick to dust.
Use a medium-nap roller to roll two coats of drywall primer over the orange-peel wall treatment. Allow each layer to dry from 2 to 4 hours. The primer covers the plaster used to create the orange-peel texture and seals the wall treatment. Do not apply pressure when rolling. Roll the paint with even, vertical strokes. Use an angled paintbrush to apply primer around the perimeter of the wall where the roller cannot reach.
Add your latex finish paint to the wall's surface. Apply the paint using the same vertical strokes used to apply the primer. Apply one to three coats of paint as needed to evenly cover the orange-peel treatment. Paint the edge of the wall's surface with the angled brush. Fewer layers may be required to trim out the room, because the paint is applied more heavily with a paint brush.