How to Paint Over an Old Rusted Metal Roof?

Painting Metal Roof

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.

However, this coating can weather and become scratched so that rust can form and penetrate the metal sooner or later.

If left untreated, holes can also develop in the corrugated metal roof 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 the lifespan of your roofing.

Repainting a Corrugated Metal Roof

Metal roof painting, in particular, offers plenty of benefits for your home. Some of these advantages include:

  • Painted metal roofs improve the aesthetics of your home’s exterior
  • Metal roofs that are lightly colored and reflective are sustainable and energy efficient
  • They can last twice as long as other materials (like asphalt shingles) and can easily be recycled at the end of their lifespan

Once you know the benefits of repainting your metal roof, here is the step-by-step process you can follow…

Step 1- Secure Yourself

Working on your roof might involve dealing with power lines and high ladders that can be risky if you do it alone.

For DIYers, it’s good to get your friend or spouse’s help so that you can work safely.

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, consider wearing non-slip shoes and a harness with a safety rope.

Do not forget to anchor the rope securely to a nearby tree or any other part of your home.

Step 2- Clean the Roof

After you have secured yourself, it’s time to get up there and perform some prepping job for your bare metal roof before painting.

First, you will want to remove the old paint layer by scraping away the loose paint – use a putty knife or a paint scraper tool.

You will need to do this gently, so you don’t damage the metal underneath.

Then with a power washer, wash your entire roof to eliminate all the paint flakes and debris.

Wait for at least an hour or two to dry the metal roof before you start with the next step.

Step 3- Apply Rust Inhibitor Primer

In this step, the goal is to eradicate the rust. So, it would help if you started by scraping the area with a wire brush.

Scrub the area with the brush until you see the metal underneath. Then, wipe the surface with a dry cloth to remove any flakes remaining.

Since you’ll want to stop the formation of the rust in the tracks of your metal roofing after painting, spray the area with a thin coat of rust-inhibiting primer first to keep the metal intact.

Allow the primer to dry before applying the roof cement to the hole.

refinishing metal roof

Step 4- Apply Roof Cement and Acrylic Mesh

Using a plastic putty knife, apply the roof cement to the hole’s edge. This is usually made from urethane and comes with waterproof properties.

Spread the cement around until you have an even coat that extends at least one inch past the perimeter of the hole.

Be sure to wear gloves as you do not want the cement to come into contact with your skin.

Once the cement is in place, cut two pieces of acrylic mesh that is at least one inch wider than the size of the hole.

If you do not have acrylic mesh, you can use the same type of metal as the corrugated roof.

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 or as long as the manufacturer’s label states.

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. The goal is to cover the area 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.

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 touch, then apply the paint evenly with a paintbrush, roller, or airless paint sprayer.

Allow the paint to dry for at least an hour and then recoat the roofing material for a durable finish.

What Paint to Choose for Metal Roof?

Corrugated metal roofs 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 for the galvanized metal roof of your home or shed; otherwise, it won’t stick well to the metal, and all your efforts go wasted.

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

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’s specifically designed to paint corrugated metal roofs when picking.

These paints should come 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 paint for metal roofs

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

Coating your old rusted metal roof with either Galvalume or paint is among the two options you can consider.

But which one is better to choose, under what conditions, and is there any advantages or disadvantages to each choice? Let’s have a look…

Galvalume is a coating for metal roofs that are much desired for its proven resistance to corrosion – in some cases, this coating outlasts galvanized steel when it comes to rust prevention.

If you aren’t familiar with Galvalume, it has been around since the 1970s. Particularly those involved in the construction industry know about this coating very well.

The basic difference between galvanized and galvalume is that galvanized steel consists of zinc, while Galvalume’s coat consists of zinc, aluminum, and silicone.

Galvalume typically makes sense if you’re looking for a low-cost, long-lasting coat that requires little upkeep.

Compared to paint on metal roofs, which lasts for two-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. The amount of money you save depends on the size 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 with this coating.

When you are to paint your metal roof, you are allowed to choose from many color options and other characteristics – but it will cost slightly more for the customizations.

Another thing is while Galvalume does protect against corrosion, it falls short in various other areas.

Like, Galvalume roofs shouldn’t be in close proximity to copper or lead because both substances can expedite the deterioration of Galvalume coatings.

Moreover, galvalume 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 are also not as versatile as paint and 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.

So, in the end, we can conclude that Galvalume offers some definite advantages over painting – but there are also certain conditions where paint is a better option.

It’s good to weigh your options carefully to decide what’s best for you and your home.

The Bottom Line

Whether it’s your barn or an outdoor shed, getting their old rusted-out metal roof repaired and repainted is easy – though it seems to be challenging in the beginning.

For many homeowners, this is so easy that they can do it themselves without professional help.

If you plan to repair and restore your metal roof yourself, all you will need is roof cement, a mesh patch, and the right paint supplies.

Hopefully, the steps above will help you get the job done fast, even if you have never done this before.

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