How to Paint a Rusting Metal Roof?

Corrugated metal roofs are typically made from galvanized steel, copper, or aluminum. Most of them are pretty strong and highly resistant to the elements simply because they are treated with a rust-inhibiting coating to prevent corrosion from occurring. In fact they can last twice as long as other materials (like asphalt shingles) and can easily be recycled at the end of their lifespan.

However, this coating can weather and become scratched so that rust can form and penetrate the metal sooner or later. If left unattended and untreated, holes can also develop in these roofs due to exposure to regular moisture.

Repairing and repainting your old metal roof with the color of your choice is the right thing to do which can extend its lifespan. In this guide, let’s explore the key steps and materials needed to paint a rusty metal roof effectively.

Repainting a Rusted Metal Roof

Light-colored, reflective metal roofs are not only energy-efficient but also environmentally sustainable.

To repaint your metal roof and enhance the visual appeal of your home’s exterior, here is a step-by-step process you should follow…

Step 1- Secure yourself

For DIYers, working on a roof might involve dealing with power lines and high ladders that can be risky if you do it alone. So to work safely, it’s good to get your friend or spouse’s help. Maybe you can thank them later for their efforts by buying them a pizza and/or a beer on your next weekend.

To work in a safe environment, also consider wearing non-slip shoes and a harness with a safety rope along with other common safety gear such as gloves, face masks, goggles, etc. Do not forget to anchor the rope securely to a nearby tree or any other part of your home.

Step 2- Clean the metal roof

After you have secured yourself, it’s time to get up there and perform some prepping jobs on your metal roof before painting. This includes:

• Scraping away the old loose paint and rust using a putty knife, paint scraper tool, or a wire brush. Do this gently so you don’t damage the metal underneath.
• Then with a power washer, wash the entire roof to eliminate all the paint flakes and debris.
• Use denatured alcohol to clean the metal roof by applying it with a clean cloth or sponge.

Gently wiping down the surface using a potent cleaner and disinfectant like denatured alcohol (isopropyl alcohol, mineral spirits, kerosene, or turpentine) will help remove stubborn grease, oil, dirt, caulking sealant, and any other contaminants. This process ensures the roof is properly cleaned before painting, allowing the primer and paint to bond effectively to the metal surface.

After cleaning, wait for at least an hour or two to dry the metal roof before you start with the next step.

Step 3- Apply the rust inhibitor primer

In this step, our goal is to inhibit future rust formation in the tracks of your metal roofing after painting.

Apply the rust-inhibitive primer without thinning, covering approximately 200-250 square feet per gallon per coat. For optimal results, two coats are recommended. Use a brush or roller to apply each coat in perpendicular directions to ensure even coverage. Do not forget to allow the first coat to fully dry before applying the second coat.

Step 4- Apply roof cement and acrylic mesh

Roof cement acts as a durable waterproof urethane sealant that adheres to the metal surface, filling in cracks, gaps, and holes. Acrylic mesh is a flexible, woven fabric that is embedded into the roof cement to enhance its strength.

When applied over roof seams, joints, or damaged areas, it adds a layer of reinforcement, making the roof more resilient to weathering, temperature changes, and structural movement. The mesh also helps prevent the roof cement from cracking over time, providing long-lasting protection. If you do not have acrylic mesh, you can use the same type of metal as the corrugated roof.

• Using a plastic putty knife, apply the roof cement to the hole’s edge by spreading it around until you have an even coat that extends at least one inch past the perimeter of the hole.
• Once the cement is in place, cut two pieces of acrylic mesh that are at least one inch wider than the size of the hole.
• Take one piece of acrylic mesh and press it into the roof cement over the hole. This will mean bending the patch as you put it into place to match the shape of the metal.
• Once in place, spread another layer of cement over the mesh patch and then lay the second piece of mesh patch over the cement. Press it firmly into place.
• You’ll want to do this for every hole in the corrugated roof and then let the cement cure for at least two hours.
• Once cured, apply another coat of roof cement over the mesh patches and be sure that all of it is adequately covered. This should create a watertight seal so that no water can penetrate.

Step 5- Apply the roof primer and paint

Once you have repaired the holes, cracks, and gaps in your old rusted metal roofing material, you can now put the primer and paint on it.

• Start by applying a thick coat of Rust-Oleum High-Performance galvanized metal primer with a specialty paintbrush or a paint roller that’s designed for corrugated roof panels.
• Apply the primer evenly to the entire surface of your metal roof, including the areas you have repaired.
• Let the primer dry to the touch, then apply the oil-based metal paint evenly with a paintbrush, roller, or airless paint sprayer.
• Allow the paint to dry for at least an hour, then recoat the roofing material for a durable finish.

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What Paints Will Stick Best to Rusty Metal Roof?

Corrugated metal roofs for homes or sheds are typically made from galvanized metal (layered with zinc to reduce corrosion). This can adversely affect the paint sticking. Picking the right type of paint is therefore vital otherwise, it won’t stick well to the metal, and all your efforts go wasted.

Oil-based alkyd paint or acrylic-latex acid paint will work best for all types of metal roofs (whether it’s a zinc roof, tin, steel, aluminum, or other rib metal).

Anti-condensation coating for metal roofs and sheds is another good option, particularly for areas with high humidity. This coating helps reduce the amount of condensation on metal surfaces, providing a long-term solution for preventing corrosion and rust.

Water-based anti-rust metal roof paints that contain rust inhibitors are also a great option and can be used. Rust-Oleum is a brand that has a wide variety of these paints available. So, you can check them out and buy the one that’s most suitable in terms of quality and budget.

No matter what paint you choose, confirm that it comes from a reliable brand with attributes such as water resistance, fire resistance, insect repellent, and better UV reflection. If there’s confusion, ask for help from a professional roofer or an employee at the hardware store.

Galvalume vs. Painted Metal Roof – What’s Better for My Home?

Coating your old rusted metal roof with either Galvalume or paint is among the two options you can consider for your home, barn, or outdoor shed. But which one is better to choose, under what conditions, and are there any advantages or disadvantages to each choice? Let’s have a look…

Unlike galvanized steel which consists of zinc, Galvalume is a protective coating made from a combination of zinc, aluminum, and silicon, primarily applied to steel to prevent oxidation.

Galvalume has been around since the 1970s, and like galvanizing, it acts as a sacrificial coating, shielding the underlying metal from corrosion. In some cases, this coating even outlasts galvanized steel when it comes to rust and corrosion prevention.

Compared to paint on metal roofs, which lasts for two to three years, Galvalume can last for several decades with minimal maintenance. Furthermore, galvalume is a less expensive alternative to painting your metal roof and will still provide the same level of protection.

Galvalume typically makes sense if you’re looking for a low-cost, long-lasting coat that requires little upkeep. However, the amount of money you save depends on the size and shape of your structure.

Limitations of Galvalume

Galvalume has certain drawbacks, which render it unsuitable for certain houses – the biggest one is the lack of color choices. Unlike paint for the metal roof where you are allowed to choose from infinite color options,  Galvalume offers very less options for customization.

Another thing to remember with Galvalume roofs is they shouldn’t be in close proximity to copper or lead because both substances can expedite the deterioration of this coating. Moreover, it should not be used on roofs for structures that will house animals. Animal waste can corrode the Galvalume coating because of the fumes it creates.

Galvalume roofs also cannot be used if you live in a coastal area because the salt in the air will cause Galvalume to corrode much faster. Painted metal roofs, however, can be used in any location, including those with high salt content in the air.