How to Repair Rusty Window Sills

Don your rubber gloves and saturate a clean rag in white vinegar. Wring the soaked rag over the rusty area. Run as much vinegar over the rusted area as possible over the course of at least 20 minutes. The best way to remove rust from smaller items such as screws or nails is to soak them in a glass of vinegar overnight.

Scrub the rust away with steel wool. Alternate between scrubbing with the steel wool and the vinegar-soaked rag. This will help loosen the rust further. Be sure to scrape away all of the rust before continuing with repair. Use sandpaper to remove the last bits of rust that are left behind.

Use a spatula to spread small layers of rust converter (also called rust remover or rust killer) over the affected area to cure any rust that is left over after your incessant scrubbing. The phosphoric acid in the solution will turn the rusted iron into ferric phosphate. Once it has cured, scrub the black solution off with steel wool and sandpaper. This will reveal a rust-free, clean metal surface.

Fill in any holes with fiberglass putty. The putty will help to recreate the rusted surface that's been worn away. Follow the manufacturer's instructions for best results. If your sill has only suffered from surface rusting, the fiberglass putty will not be necessary.

Sand down the fiberglass putty to match the texture of the sill. Paint over with a clean metal primer to protect the sill from further rust damage.