Rust is the enemy of outdoor metal objects. Left unchecked, rust can quickly damage and destroy metal surfaces exposed to the elements. Preventing rust on outdoor metal requires vigilance and proper care, but is absolutely worth the effort for preserving items you want to last. With some simple tips and techniques, you can keep outdoor metal looking great and rust-free for years.
Why Outdoor Metal Rusts
Metal rusting is a complex chemical process, but the basics are pretty simple. For rust to occur, three things are needed:
- Metal – Most types of metal can rust. Iron and steel rust easily, while other metals like aluminum are more resistant but can still oxidize.
- Water – Moisture is required for the chemical reaction of rust to take place. Wet weather, humidity, rain, snow, and dew all provide the water.
- Oxygen – The corrosion process requires oxygen to create rust. Outdoor air naturally supplies oxygen.
Exposed to these three ingredients, the surface of metal slowly oxidizes as rust forms. Tiny pits and cracks gradually develop across the surface as rust expands and flakes away more metal. Once started, rusting is self-perpetuating as the corrosion process continues eating away more metal.
Outdoor metal rusts much faster than indoor items. Frequent moisture from the weather accelerates rusting. And sunlight, pollution, salt, and other environmental factors also speed up the corrosion process. So outdoor metal requires proper care to prevent unchecked rust damage.
Preparing Outdoor Metal Surfaces
Before applying preventative measures, thoroughly clean the metal to remove any existing rust and create an optimal surface. Here are some tips for prep:
Remove loose rust – Use a wire brush, sandpaper, steel wool, or a power tool like a grinder to scrub away all loose, flaking rust and scale. Remove it down to bare metal.
Clean deep rust – For rust that’s deeply pitted or permeated the surface, you may need to use a chemical rust remover or acid solution. Products like naval jelly help dissolve difficult rust and etch the metal surface.
Clean and dry – After removing all rust, wash the metal with soap and water to remove debris and dust. Let the surface dry completely before moving to the next steps.
Sand and smooth – Lightly sand the clean metal with fine sandpaper. This smoothes the surface for paints or coatings to properly adhere.
Proper metal prep provides the cleanest slate for your rust prevention measures. Remove every trace of rust now to slow down corrosion later.
Rust-Blocking Paints and Coatings
Applying protective paints and coatings is the most common and effective way to prevent outdoor metal rust. Quality products create a barrier separating the metal from moisture and oxygen to stop the rusting process. Consider these types of coatings:
Rust-Inhibiting Primers
Primers enriched with rust-fighting chemicals are ideal for heavily rusted or hard to protect metal. The primers sink into pores and etch the surface as they dry. This anchors the coating while forming an impenetrable seal against moisture. Some good options include:
- Rusty Metal Primer – Forms a tough acrylic shield against corrosion.
- Rust Reformer – Transforms rust into a paintable surface and stabilizes metal.
- Zinc-Rich Primers – Zinc particles neutralize rust and galvanize metal.
Outdoor Paints
A fresh coat of exterior paint brings colour while sealing and protecting metal siding, fixtures, railings, and anything else in the elements. Opt for top-quality paints designed for metals and outdoor use. Consider:
- Exterior acrylic latex paint – Flexible water-based acrylics adhere well.
- Oil-based alkyd enamel – Harder finish resists chipping and fading.
- Rust-inhibiting paint – Metal paints with anti-rust formulations.
- Weather-resistant paint – Withstands sun, rain, snow, and temperature swings.
Clear Metal Coatings
Clear coatings prevent rust while allowing the natural metal shine to show through. Common options include:
- Clear polyurethane – Durable plastic coating with a glossy finish.
- Clear epoxy – Two-part coating with excellent adhesion and resistance to abrasion.
- Wax coatings – Protective wax films repel moisture naturally.
- Lacquer – Fast-drying and glossy, but less durable for outdoors.
Specialty Outdoor Coatings
For added protection against the elements, look to industrial coatings:
- Galvanization – Hot-dip zinc coating creates cathodic protection.
- Powder coating – Electrostatically applied plastic powder.
- Electropaint – Water-based paint applied via electrodeposition.
Proper prep and application are key for any coating to effectively prevent rust. Follow manufacturer directions carefully including number of coats and cure times. Re-apply protectively every 2-3 years or when wear appears.
Maintaining Painted & Coated Surfaces
Regular maintenance preserves the protective finish you’ve applied. Keep surfaces clean, dry, and carefully monitored to avoid new rust.
Wash regularly – Clean painted metal once or twice annually using mild soap and water. Avoid abrasive brushes or cleaners that wear down the finish.
Inspect for damage – Check for any chips, scratches, wear, or fading in the coating that expose metal. Touch up immediately.
Re-apply protectants – Re-coat surfaces before rust appears. Every few years is ideal. Wax coatings need re-applied every season.
Dry wet metal – Quickly dry any moisture from rain, sprinklers, etc to prevent pooling water from starting rust.
Spot clean rust spots – Use sandpaper, steel wool, or naval jelly to remove any rust pits or spots that appear. Re-paint.
Avoid salts and spills – Rinse off road salt in winter. Clean any chemical spills quickly before damage.
Check hidden areas – Look for rust starting in concealed spots like the underside of railings.
Rust Protection for Specific Metals
Certain types of metals have particular vulnerabilities or requirements when preventing outdoor rust.
Cast Iron
Cast iron rusts more slowly than steel but still needs protection. Coat with primer first, then outdoor enamel paint. For a natural look, boiled linseed oil protects cast iron without painting. Wax coatings also work well. Keep drain holes clear.
Wrought Iron
Apply a zinc-rich primer first for wrought iron. Follow with outdoor paint. Lacquer finishes look nice but need frequent re-application. Control runoff and pooling water to prevent rust streaking on decorative wrought ironwork.
Stainless Steel
Quality stainless steel is highly rust-resistant. But exposure to saltwater or de-icing salts requires extra care. Use paint or wax on stainless for additional protection. Rinse off any salt residue and wipe away standing water or condensation to prevent pitting.
Aluminum
Aluminum forms an oxide layer that resists corrosion. But heavy moisture exposure risks white surface corrosion. Use aluminum paint or clear coatings. Anodized aluminum has added protection. Avoid contact with other metals to prevent galvanic corrosion.
Copper
Natural copper patinas but resists rusting. Apply lacquer or wax if oxidation is unattractive. Prevent contact between copper and iron/steel as this accelerates galvanic corrosion. Rinse acidic pollutants like bird droppings quickly.
Galvanized Steel
The zinc coating of galvanized steel provides cathodic protection at scratches or cut edges. Painting isn’t required but adds an extra barrier. Touch up scratches with zinc-rich primer. Avoid exposure to saltwater which removes the zinc layer.
Other Rust Prevention Methods
Beyond paints and coatings, a few other tactics help fend off external corrosion:
Weather Protection
Keep metal sheltered from the elements whenever possible. A covered porch, shed, or garage protects from rain and snow. Use covers or tarps to shield metal furniture or equipment when not in use.
Sacrificial Anodes
Attach a more easily corroded “sacrificial” metal like zinc or magnesium to steel to counteract electrochemical rusting. The sacrificial anode corrodes before the protected metal.
Cathodic Protection
Connect an external power source to make the metal a cathode, reversing the rust reaction. Used to protect pipes, boat hulls, steel piers, and more industrial metal assets.
Oil & Grease
Thin films of oil, grease, or petroleum jelly can temporarily prevent rust on small tools or surfaces. Re-apply frequently as protection washes away over time.
Desiccant Packets
Seal metal items in airtight containers with silica gel or calcium chloride packets to keep the interior very dry and moisture-free. Helpful for long-term storage.
How to Remove Rust from Outdoor Metal
If your prevention efforts fail and rust sets in anyway, prompt removal keeps it from getting out of control:
- Light rusting – Wipe with steel wool or sandpaper. Scrub gently to avoid damaging good metal.
- Surface oxidation – Use a vinegar or phosphoric acid solution. Let it sit before scrubbing.
- Deep rust – Apply rust remover chemicals. May need to soak overnight and scrub repeatedly.
- Pitted rust – May need to grind or sand down to remove all corrosion.
- Rust streaks – Use detergents like TSP or ammonia applied with a stiff brush.
Preventing those rust stains and pits in the first place is much easier than trying to remove extensive corrosion after it occurs!
Commonly Asked Questions About Preventing Rust on Outdoor Metal
Rust prevention does require some diligence and upkeep. Here are answers to some frequently asked questions:
Should I remove rust before painting metal?
Yes! For the best results, remove all loose rust and flaking paint down to bare metal before repainting. Any rust left under paint will continue spreading.
How often should you re-paint outdoor metal?
Typically every 2-3 years, or whenever you notice wear and cracks appearing in the previous coat. More frequent re-painting is needed in harsh coastal or industrial environments.
What kind of paint adheres best to outdoor metal?
Exterior latex and oil-based alkyd enamel paints adhere well when applied over the proper primer. Rust-inhibiting paints also bond tightly.
Can you use the same paint on different metals?
Yes, the same outdoor paints and coatings can be applied to iron, steel, aluminum, etc. But remove any residue from other metals first to get optimal adhesion.
How do you paint rusted metal furniture?
First remove loose rust with sandpaper or steel wool. Wipe clean, then apply a rusty metal primer before topping with an outdoor enamel paint in your desired color.
What is the best protective clear coat for metal?
For outdoor use, clear polyurethane forms an extremely durable and waterproof coating. Clear epoxy is another excellent option for exposed metal items.
How do you waterproof outdoor metal art?
Clean the piece then apply an exterior polyurethane sealant. Use multiple coats for maximum protection, especially on intricately detailed artworks.
How often should metal patio furniture be painted?
Touch up any scratches/flakes annually. Fully repainting patio sets every 2-4 years helps the finish last against sun, rain, wind, and snow.
Can car wax be used on outdoor metal?
Yes, carnauba paste wax can help repel water and prevent rust on small metal pieces. Apply a couple coats and buff out. Re-apply every few months.
Conclusion
Preventing rust on outdoor metal does require some work – proper prep, painting, maintenance, and vigilance against early signs of corrosion. But a sound prevention strategy will pay off for years protecting your valuable metal objects, equipment, and structures from rust damage. A regular investment of elbow grease and paint now will prevent much more laborious restoration work later if rust is allowed to run unchecked.
Following these tips of cleaning, coating, monitoring, and regularly re-applying protective paints or finishes will help your outdoor metal maintain its luster and structural integrity. While some surface oxidation may occur, catching it early keeps corrosion controlled. With the right prevention plan, your outdoor metal can remain rust-free and look great for many seasons before showing any significant wear. Implementing proactive anti-rust measures makes enjoying lovely architectural details, furniture, railings, and fixtures possible even in harsh outdoor settings.