How to Scrape a Window Sill Before Painting

Clean the window and window sill with detergent, water and a scrub sponge if it's very grimy. Built-up dirt and grime will make scraping more difficult.

Lay heavy plastic or a drop cloth under the window to catch chips of old paint.

Hold a stiff one- or two-inch putty knife at an angle to get under the edges of the loose paint between the substrate and the paint and push the paint from the surface. If the sill is wood, take care not to gouge it.

Use a pulling-type scraper, sometimes called a double-edged scraper, for multiple layers of paint. Bear down on the scraper as you pull it across the surface with enough force to break up the paint layers. Use the putty knife to pry the cracked, loosened paint away from the surface.

Scrub masonry or brick window sills vigorously with a wire brush to get small shreds of paint from the crevices and cracks in the surface. Don't use a wire brush on wood sills; it will scratch and damage wood.

Sand wood sills after scraping to smooth down the edges of the remaining paint and provide a better surface for the primer and paint to adhere to. Use 80- or 100-grit sandpaper if the wood is in good condition. Use a power sander and 80- or 50-grit sandpaper to sand down old and deteriorated wood.