Sand using medium-grit sandpaper to smooth and level patched areas or areas with imperfections in the previous paint film (e.g. bubbles, rough spots or cracks). Then, wash the walls with a mild soap-and-water solution to remove sanding dust.
Sanding to Degloss
Sanding walls for painting is also important if you plan to repaint a surface that has a shiny finish. It's called deglossing and it helps the new paint adhere properly. To degloss, first wash the surface with a mild soap-and water-solution and let dry. Next, sand the walls and trim with medium-grit sandpaper to dull and create a profile for the new paint to adhere. Use a damp cloth to remove the dust.
Removal of old finishes by sanding, scraping or other means may generate dust or fumes that contain lead. Exposure to lead dust or fumes may cause brain damage or other adverse health effects, especially in children or pregnant women. Controlling exposure to lead or other hazardous substances requires the use of proper protective equipment, such as a properly fitted respirator (NIOSH-approved) and proper containment and cleanup. For more information, call the National Lead Information Center at 1-800-424-LEAD (in the U.S.) or contact your local health authority.