How to Paint a Rusty Metal Roof [Step-by-Step Guide]

If you live in an area with a lot of tree coverage, then no other roof can match a metal roof for its ability to shed leaves, twigs, water, and more. But like all metal items left out in the elements, metal roofs are susceptible to oxidation and rust. Once rusted, a once beautiful metal roof now looks haggard and old.

If you find yourself in a similar situation, then you’re probably wondering what can be done to refinish your roof and make it look new again, short of actually redoing the roof. A new roof could be quite expensive, so what’s the alternative?

Luckily, you can breathe new life into your old, rusted metal roof. It’s going to take a bit of work and a few helpful products, but it can be done. Let’s take a look at what we’ll need to tackle this job and the steps we’ll have to take once our supplies are gathered.
How to Paint a Rusty Metal Roof

Can You Paint Over a Rusted Metal Roof?

The obvious first question is: can you paint over a rusted metal roof? It would be extremely convenient if all you had to do was slap a new coat of paint onto that aging, corroded old roof.

Well, you can but it’s going to take a few more steps than just painting it and calling it a day. Before we can even think about painting, we’re going to have to do something about that rust.

First, we need to remove as much of that rust as possible. Next, we need to prevent the corrosion from continuing to expand.

To take care of the first step, removing the rust, we’re going to need to physically attack the rust and remove as much of it as possible by force.

For halting the rust in its tracks and ensuring that it won’t continue to eat through our new coating and degrade the existing metal any further, we’re going to use a special primer with a rust killer built-in. Once coated with the rust killer, the oxidation will no longer be able to grow and weaken your roof.

How to Paint a Rusty Metal Roof

Painting a metal roof isn’t much different from painting any other metal surface. You’re going to need to follow the same basic steps: preparation, primer, paint.

1. Remove Rust From a Metal Roof

Removing the rust from your metal roof is going to take some physical work. To do this, there are two major methods you could employ.

The first method is going to utilize chemicals to attempt to neutralize the rust and weaken it so that you can then remove it with a scrub brush.

For the second method, you’ll need to employ the help of a pressure washer.

Before attempting either method, ensure that you’ve removed the largest flakes of rust from your roof with a dry scrub brush.

Method 1: Trisodium Phosphate

Savogran 10622 4.5 Lb. TSP All-Purpose Heavy Duty CleanerTrisodium phosphate can penetrate the rust and help to remove stains and prevent the rust from continuing to grow. It’s a common chemical that you can find at most local home improvement stores.

A word of caution: be careful when using trisodium phosphate. It’s a harsh chemical that’s very effective at what it does, but you don’t want to get it on your skin, clothes, eyes, or anywhere else. Make sure to wear rubber gloves and clothes that you’re concerned with getting destroyed, just in case.

You’ll need to dilute the trisodium phosphate before applying it. It comes in a powdered form but will need to be mixed with water at a ratio of one cup trisodium phosphate to one gallon of water.

Once mixed, you’ll need to apply it to any rusty areas using a sprayer. Give it a good 15 minutes to penetrate the rust and start working. Then, using a hard-bristled scrub brush, scrub all of the rust and remove as much of the staining as possible.

Method 2: Pressure Washer

Sun Joe SPX3000 2030 Max PSI 1.76 GPM 14.5-Amp Electric High Pressure Washer, Cleans Cars/Fences/PatiosIf you don’t want to scrub by hand or you’d rather not expose yourself to the harsh trisodium phosphate, then you can opt for the mechanical method instead.

You’ll need a pressure washer to make this work, and it needs to reach at least 2500 PSI if you want to remove the rust from your metal roof.

Simply turn up the pressure and start spraying. Make sure to hit the entire roof, knocking loose any flakes of rust, and spraying off as much of the oxidation coloration as possible.

Combining Methods

Though pressure washers and trisodium phosphate are both effective for removing rust and stains from your roof, their effectiveness can be compounded when you use them together. If you have access to a pressure washer and don’t mind using the harsh chemicals, combining these methods can give you the best results.

First, apply the trisodium phosphate to the roof and give it about 15 minutes to soak in and start loosening up the rust. Then, turn the pressure washer up to a minimum of 2500 PSI and start spraying off the rust and discoloration.

With this method, you likely won’t need to scrub by hand at all. You can just let the chemicals and machines do all the work.

2. Wipe the Roof Down With Vinegar

Because corrugated metal roofs are made with a galvanized coating to prevent corrosion, the paint is going to need some help if we want it to stick. So, we need to neutralize the zinc with an acid. We’re going to use white vinegar since it’s completely natural, inexpensive, easy to find, and completely harmless to you.

Apply some of the white vinegar to a rag. Then, use the rag to wipe down the roof. You don’t have to scrub hard, just lightly apply the vinegar to the entire roof. Be sure not to miss any areas!

3. Apply Primer

It’s finally time to start watching the roof change. The vinegar from the previous step should evaporate pretty quickly, so you won’t have to wait long before you can start applying your primer.

If we use the right supplies, we can ensure that our paint adheres properly and the rust never returns to our metal roof. The question is: what are the right materials to use?

In this case, it all starts with the right primer. Since we’re dealing with an old, rusted surface, we need a primer that’s going to stop that rust from continuing its slow, ruinous ways. Luckily, there are special formulas available that do precisely this, turning your rusted old roof into a fresh surface that’s ready for repainting.

As with any time you paint, start by reading the instructions on your primer can to get any detailed or specific instructions from the manufacturer.

You can apply the paint using a roller or a paint sprayer. Technically, you could use a paintbrush or even a spray can, but those would be very time-consuming methods for painting an entire roof unless your roof is very small!

Make sure to apply the primer as evenly as possible and don’t miss any spots! Also, be careful about painting yourself into a corner; literally! Once you paint an area, you won’t be able to walk on that area again. So paint yourself towards your ladder so you have a way to get back down from the roof when you’re finished!

Once the primer is even applied and you’ve covered the entire roof, you’ll need to wait for it to fully cure before applying your paint. Check the can for specific instructions about how long this will take. For most primers, you should be ready for paint within 24-48 hours.

4. Apply Paint

Painting rusted galvanized metal roof

After coating your once-rusted roof with the rust killing primer, it’s time to paint. While you can use standard exterior paint at this point since the roof is already primed, it’s preferable to add another layer of protection and use a rust-preventative paint with a protective finish that will help ensure your roof doesn’t need another paint job anytime soon.

A word of caution: check the weather before you paint the roof! If a storm comes in while your paint is wet, it’s going to ruin all the hard work you’re about to do. Worse, it’s going to make a massive mess that you’ll have to clean up. Save yourself some trouble and check the weather report before beginning any type of exterior paint job.

Make sure the primer is completely cured before attempting to paint. Painting while the primer isn’t fully cured can result in the ruining of your paint job, requiring you to remove it all and restart. That’s a lot of wasted time for an impatient mistake!

Once you’re satisfied that the primer is completely cured and ready for a coat of paint, you can apply the paint the same way you applied the primer. Using a roller or a paint sprayer are your most efficient methods but you’re free to apply the paint however you’d like.

Again, be sure to get even coverage on the whole roof. You don’t want areas of thicker or thinner paint application because these will likely show when the sun is reflecting off the roof.

5. Final Coat

It’s possible that your roof doesn’t require any additional coats of paint. It’s already been covered with primer and protective enamel, so it’s safe from the elements and well-protected.

But take a look at the finish of your roof. Look closely for darker or lighter spots where the paint was applied more or less heavily, particularly in the sunlight. If you find a lot of these areas, you’ll want to apply an additional paint coat for aesthetic purposes. Once it’s dry, your once-rusted roof is now nearly as good as new, and it might look even better than it did when first installed.

Best Primer for Rusted Metal

Rust-Oleum 7769730 High Performance Rusty Metal PrimerSo, what is the best primer for coating that rusted metal roof? There are quite a few good products on the market, but my favorite is the Rust-Oleum High-Performance Rusty Metal Primer. Its formula is made specifically for rusted metal surfaces and it stops rust where it is so it can’t continue spreading and ruin your new paint job.

Rust-Oleum is one of the biggest and most respected names in metal painting, particularly rusty metal; it’s right in their name! Like many of their products, I’ve had great success with the High-Performance Rusty Metal Primer. It adheres well and goes on easily and smoothly.

Luckily, this formula comes as a liquid instead of a spray so you can easily use it to cover your entire roof. It would be a nuisance trying to do that with spray cans! Plus, this primer dries pretty quickly and will be ready for a coat of paint the day after you apply it.

Best Paint for Galvanized Metal Roof

Corrugated metal roofs are made from galvanized metal. If you’ve ever attempted to paint a galvanized metal surface before, you know that paint doesn’t adhere well. During the galvanization process, zinc is layered on the metal to reduce corrosion, which can have the adverse effect of shedding paint.

RUST-OLEUM 215965 Enamel Paint, 128 Fl Oz (Pack of 1), Regal RedTo combat this, we’re going to implement several simple measures. First, we’re going to wipe down the roof with white vinegar. Since vinegar is an acid, when you apply it to the galvanized metal, a reaction will take place on the surface that promotes paint adhesion.

Next, we’re going to use a primer that will allow us to safely apply whatever paint we prefer on top. But we’re taking things a step further by also using a high-adhesion protective enamel as our final topcoat.

I’ve used quite a few of these products, but once again, my favorite is a Rust-Oleum. This time it’s the Rust-Oleum High-Performance Protective Enamel. It’s corrosion-resistant and extremely durable, helping to protect your metal roof from nature’s wrath.

To help aid with the prevention of rust, this formula is rust-preventative. It also looks incredible and has great coverage, but it’s really the long-lasting durability that earns it the win from me.

Conclusion

It likely seems like a daunting project to take on that dilapidated-looking old rusted-out metal roof. But a few hours and a new coat of paint can revitalize that roof and transform the look of your entire home. And you can do it yourself so it doesn’t have to be expensive. Just follow the steps I’ve laid out here and in no time it will feel like you’re pulling up to a brand new home every time you pull into the driveway.

If you found this article helpful in any way, I’d appreciate it greatly if you could help me reach others with this information by sharing it. And if you have any questions or comments, leave them in the comments box below and I’ll respond as quickly as I can.

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