Metal makes a durable door option, but it's also the potential target of rust. While a little surface rust doesn't affect the strength of the door, it does make it look dingy and outdated. With a little elbow grease and the right tools, you can smooth away the rust and repaint the metal door to make it look fresh and new.
Sand the Rust
You can use a rust remover chemical, but if you prefer to avoid chemicals, sanding is often an effective way to get rid of door rust. The extent of the rust determines how tough you need to get with your sanding, grinding or brushing. If you're dealing with a small patch of rust, you may be able to smooth it away with a piece of sandpaper or a sanding block. Go over the area with the sandpaper using a circular motion until you remove all of the rust.
Use a Wire Brush
A sturdy wire brush is often the best way to remove rust in grooves or other difficult to reach areas because the bristles can get into those small spaces. You can also use the wire brush on other parts of the door. Scrub the rust in a circular motion, being careful not to press so hard that you scratch the door.
Apply Household Items
You may have some luck with vinegar or baking soda. For the vinegar method, apply the liquid using a sponge and give it 30 minutes or so to work on the rust. You can apply more vinegar if needed to get rid of any remaining spots.
A baking soda and water paste may also help work away the rusty spots. Apply the paste to any rusty areas, leaving it for 30 minutes. Use a soft cloth to remove the paste.
Remove Rust With a Grinder
If you need more muscle behind your rust removal, you can use a grinder, drill or sander to power through the rust. Attach a stripping disc, grinder wheel, fiber disc or similar attachment that's appropriate for use on metal. Starting with a coarse disc helps remove the bulk of the rust efficiently. Change to a fine-grit disc after removing the rust to get a smooth finish without swirls or grooves in the metal.
Clean and Prep the Surface
Before you can repaint the metal door, you need a clean, smooth surface. Go back over the door with sandpaper if needed to smooth out any rough or uneven areas. If the door has any gouges or dents, either from the rust removal process or from previous damage, fill them in with auto body filler putty, smoothing it on to blend into the area. Sand the area with a fine-grit sandpaper after it dries according to the package instructions to smooth out the patched area.
Once you have a smooth surface, wash the door to remove any dust particles, grime or other gunk that will keep it from holding paint. Let the door dry completely before priming and painting.
Prime the Metal Door
Priming the metal doors is an important step to ensure you get a smooth finish. Primer can also help prevent future rust on the door. Choose a primer designed specifically for metal and for outdoor use if you're painting an exterior door.
A spray primer is often easier to apply in even layers without brush marks. Follow all instructions on the primer, holding it a consistent distance from your door and applying in a thin, even coat.
Repaint the Metal Door
Your paint choice can also help prevent future rust. You can get rust-inhibiting paint with zinc additives designed for use on metal. Like primer, paint options include brush and spray options. Removing the door from its hinges may make painting easier to prevent drips, but you can also paint it while it's still hanging.
Whether you brush or spray paint the door, use thin coats to build up to the coverage you want. The thinner coats produce the best finish without thicker areas or drips. Wait for the paint to dry before you apply each coat.