How to Paint Over Rusted Metal
From prep to primers to paint, here's what you need to know to achieve professional, long-lasting results when painting over rust.
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Rust, that powdery-to-flaky brownish-red substance familiar to all of us, is a byproduct of a chemical reaction (oxidation) between iron or steel, water or moisture and oxygen.
Brad the Painter, a professional painter for more than 30 years, has seen his share of rust on the job. “Steel or any metal that has iron will rust unless it’s coated with the right stuff,” he says. “Galvanized metals and brass do not rust, which is why you find them in plumbing parts.”
Left untreated, rust will eventually eat through a panel of a car or a wrought iron patio table. Painting is an easy and economical way to prevent rust from corroding outdoor furniture, gutters, garden tools, gates, barbecue grills and more.
Take San Francisco’s Golden Gate Bridge. According to the Golden Gate Bridge Highway & Transportation District, “Painting the bridge is an ongoing task and a primary maintenance job. The paint applied to the bridge’s steel protects it from the high salt content in the air which can cause the steel to corrode or rust.”
Note: Corrosion is a breakdown of metal from a chemical reaction. Rust is a type of corrosion that is specific to alloys made of, or containing, iron.
How To Paint Over Rust
If you have something that has already started to rust, here’s what to do to stop it from getting worse.
Tools and Supplies Needed To Paint Over Rust
Make sure you have everything you need before you begin.
- Wire brush;
- Sanding block or orbital sander;
- Power drill with wire wheel attachment (for heavy rust);
- Drop cloth;
- Paintbrush, sprayer or roller (with cover);
- Detergent or degreaser;
- Rust neutralizer;
- Rust-resistant primer;
- Paint with rust inhibitor.
Preparing To Paint Over Rust
There’s no substitute for properly preparing a metal surface for painting. It’s key to achieving a beautifully protected surface and a professional finish.
The first step is to remove loose rust and any chipping or peeling paint. Use a wire brush or fine-grit sandpaper. If you’re dealing with heavy rust damage, a power drill with a wire wheel attachment will quickly sand down the surface to a dull, matte finish.
Many experts recommend treating a rusty surface with a rust neutralizer, which converts its chemical composition. (Note: If you opt for this step, the manufacturer recommends waiting 48 hours after application before priming or painting.)
Next, clean the item with an ordinary household detergent or degreasing agent to remove dust, dirt and oils. Let it dry thoroughly before moving on to the primer step.
Remember, if you don’t prep properly, your project won’t look good for long no matter what type of paint you use.
Primer for Rust
A primer is designed and formulated to seal a surface, as well as provide a “tooth” (a roughness of surface produced by mechanical or artificial means) for paint and other topcoats to bind to. Creating a barrier that contains a rust inhibitor is important for keeping it from coming back.
If you’re looking for an excellent oil-based primer, consider Rust-Oleum flat rusty metal primer, which performs especially well on heavily rusted areas. For an all-surface water-based option, the highly-rated Rust-Oleum Zinsser Bulls Eye 1-2-3 Primer works with alkyd and acrylic formula paints.
If you’ve chosen dark paint, a tintable primer base that’s close to the topcoat color helps speed the process along by reducing the number of coats of paint you’ll need.
Pick Anti-Rust Paint and Coat It
When searching for the right paint for your project, choose one identified as “anti-rust,” “rust inhibitor” or “rust-resistant.”
For paint that’s tough and durable, an oil-based (alkyd) formula is your best bet. Oil-based paints not only provide a uniform finish but also bond tightly to metal and are less likely to fade. For painting an outdoor fire pit, wood stove or barbecue grill, using high-heat paint is imperative.
Apply paint over rust with a brush, roller or sprayer. Your choice should be based on the size and characteristics of the surface you’re painting. For instance, if you’re painting something textured or intricate, such as a wrought iron garden bench, a small paintbrush gives you much-needed precision and control.
Using spray paint from a can or a sprayer is a fast and efficient way to paint things like a mailbox or weather vane. Be sure to work in a well-ventilated area, avoid working outdoors on windy days and leave plenty of room to account for overspray. For large, flat metal surfaces, like tables and garage doors, a roller with a short-hair cover is an easy and efficient way to lay down a smooth, brushstroke-free finish fast.
Once the first coat is dry, check the coverage to determine if a second or third coat is required.
Add a Topcoat
It doesn’t hurt to go the extra mile when painting over rust. If you want an extra layer of durability or an ultra-shiny finish that lasts, you can add a clear topcoat product.
Let It Dry
Respect the manufacturer’s drying times. It wouldn’t hurt to exceed them if you have the patience. Make sure to follow the recommended recoating times as well. Recoating too soon can cause surface wrinkles, dimples or bubbles.
Cure time is the period it takes paint to fully harden. Cure times vary, depending on the type of paint (oil- or water-based) as well as the surrounding temperature and humidity. It can take anywhere from one week to several months for a painted surface to completely cure.
Protect the New Paint
Just like the Golden Gate Bridge, your newly refreshed metal object will need touch-ups or re-painting from time to time. To extend the life of your outdoor furniture and equipment, use protective covers to keep moisture away and store them indoors during the off-season.