Many homeowners can be intimidated by the possibility of trying to paint window sills because sills are consistently exposed to the elements and require careful preparation before being repainted. Follow these steps to do it right.
Prepare the room. Repainting can be messy, so protecting the room is essential. Move furniture and other objects away from the window and cover with durable, heavy-duty drop cloths. Use painter's tape to mask the edges of the wall along the window sill.
Prepare the window sill. Open the window all the way and secure it in place. Carefully remove loose or flaking paint with a paint scraper. Chemical strippers can be used if needed, but create noxious odours. Use an industrial fan to remove vapours when using a chemical paint stripper.
Caulk any gaps between the window sill and the wall. Remove nails or other protrusions and patch any holes in the window sill. Allow repairs to dry thoroughly.
Turn off the fan and wear a dust mask. Use a palm or block sander and medium-grit sandpaper to sand the window sill as smooth as possible. Remove dust with a damp rag.
Use a wide brush to apply exterior-grade primer. Consider adding a stain blocker to increase protection. Allow to dry thoroughly. Use fine-grit sandpaper to create a smooth, sleek surface, and then remove dust with a damp rag.
Use a wide brush to apply exterior-grade paint. Semi-gloss is a popular choice for window sills, although high gloss may also be used. Work quickly but carefully, stepping back frequently to look for drips, runs or thin spots. Use a narrow brush to paint the edges of the sill. Align the brush against the painter's tape and make each stroke away from the tape. Allow to dry overnight, and then add a second coat if needed.
Remove the painter's tape as soon as the paint is dry. Allow the paint to dry thoroughly before closing the window. If the weather is warm, let the paint dry for three days. If the windows must be closed at night, paint window sills in the morning and gently close the windows just before bed.