Whitewashing over stained cabinets is possible, but it will take some extra work. First, sand the cabinets lightly to rough up the surface and help the whitewash adhere. Next, apply a primer specifically designed for covering stained surfaces. Once the primer is dry, apply a white paint, using a brush or a roller designed for painting cabinets. Finally, seal the paint with a clear topcoat to protect it from wear and tear.