Crystal knife is a high quality extra clear polyester mastic used to vertically or horizontally: Repair | Rebuild | Bond | Fill | Crystal is very smooth in consistency, and will cure shiny, is very polishable and colors easily to match granite and other stones. It is perfectly suited for any application where the adhesive or seem/joint must be hidden. It cures fast and bonds extremely strong. Cures in lower temperatures. Not suitable for temperatures below 32°. Recommended for interior use. UV resistant.