Remove Popcorn Ceiling Texture
Cover the floors, walls and furniture with plastic drop cloths and seal the seams with masking tape. Even removing small amounts of popcorn ceiling texture can cause a lot of dust that's difficult to remove. Measure the width of the top of your crown molding. If it's one inch wide, plan to remove one inch of popcorn ceiling texture in every location you plan to install crown molding. Scrape the tip of a putty knife across the surface of your ceiling to remove the popcorn texture. Remove only the texture where you plan to install your crown molding unless you plan to retexture the entire surface of your ceiling. Using a tool the same size as the width of your crown molding will make this go easier. For example, if the top of your crown molding is one inch, use a putty knife that's 1 inch wide when you remove popcorn ceiling texture.
Install Crown Molding
Measure the length of each wall where you will install crown molding. Write these measurements down. Cut your crown molding to size so it runs from one corner to the next. Use a miter saw to cut the corners at a 45-degree angle so the corners butt up together. You may use power tools to make all of your cuts, but a miter box and a simple hand saw work just as well. Apply a bead of caulk to the back edges of your crown molding. Caulk is a strong adhesive and will secure the crown molding to the wall without the assistance of nails. This means you don't have to worry about filling and painting over nail holes after you install crown molding. Press the crown molding against the wall and hold it briefly while the caulk secures to the wall. Use a damp cloth to wipe away any excess caulk that seeped out around the edges. Caulk any gaps or imperfections between the molding and the ceiling or in the corners. Using painter's caulk in these spaces will cover the flaws. Paint over the area so it blends in smoothly with the rest of your crown molding.