Painting different sections of a room with separate colours provides a different look and a focal point to that room. Many people paint the same colour over an entire window frame without thinking outside of the box. Painting the window sill a different colour than the rest of the frame can add an alternative style to the window treatment that surrounds the frame. You must prepare the window sill before it's painted, to ensure a lasting finish to the surface.
Remove any peeled paint from the sill with a scraping tool. Use a stiff brush to dust the remaining paint chips from the window.
Wash the window sill with a combination of one part mild detergent to three or four parts warm water. Rinse with warm water and let dry completely. Clean the sill with a deglosser before continuing. The deglosser removes grease and grime from the area.
Scour the sill with 120 grit sandpaper to smooth out any rough edges. Wipe the sill with a clean tack cloth afterward. The tack cloth eliminates dust particles from the sandpaper that could leave a tacky finish.
Add painter's tape to any parts of the window that you don't want to paint. Larger areas can be covered with cardboard before applying the painter's tape. Apply tape below the sill so the paint cannot drip down onto the wall.
Place a dust sheet under the area in which you'll be working. The cloth protects the floor beneath the window sill from paint spills or splashing.
Open the paint can with the metal paint can opener, stir the paint with the wooden stir stick, and pour into the paint tray. Dip the paintbrush about half way down the bristles.
Apply smooth even strokes to the window sill, starting with the flat ledge. Continue to paint the corners then the bottom of the sill. Since you have painter's tape underneath the sill, paint won't drip down the wall if you are careful. Allow the paint to dry as instructed on the paint can before continuing.
Review the window sill before applying a second coat of paint. You may not need a second coat; look for missing paint and streaks. If a second coat is needed, you can apply it the same way as the first coat of paint.
Add a coat of varnish to the window sill if you place plants or water related items on the ledge. This will protect the sill from water damage. Read the varnish instructions carefully before applying as there are many brands of varnish, with different instructions. Use a different brush to apply the varnish than you used for the painting.
Wear a dust mask when sanding any areas of the sill. Open a window in the room before applying the varnish as it has strong fumes that may make you sick.