Painting a Metal Roof

Painting a Metal Roof

Introduction

This article is meant to clarify the answers to some of the most common questions our customers have about painting a metal roof. This information is aimed at the residential customer, but can easily pertain to a commercial application as well. However, commercial facilities will have other more industrial product selections such as epoxy and aliphatic urethane coatings to choose from that are less common in a residential environment. These types of coatings will not be covered in this article. Product selection will be limited to more readily available products with less involved application procedures.

 

This article is broken down into four basic sections. The first step is to determine what substrate you are painting actually is. This includes both the type of metal and any existing coatings that are in place. The second step is to determine the best method and products to prepare the existing surface for paint. The third step is choosing the correct coating system for the job. The final section will cover some of the dos and don’ts of applying the coating.

 

Please read through the entire article before beginning your project to familiarize yourself with the process as a whole. It’s all too easy to jump right into a project and find yourself suddenly overwhelmed.

Determining the Substrate

The first step in painting any metal roof is determining what substrate and existing coatings you are dealing with. This is a huge factor in what coating system you’ll want to use and is critical to determining how to prepare the existing surface.

 

There are several different types of metals used in roofing applications. Some are more common than others. Historically steel and copper have been widely used. Stainless steel and aluminum are newer and more expensive products used in roofing applications and as a result are less common. There are also various Terne products available. Terne is an alloy of a few different metals that is used to coat a steel core and provide anti-corrosion properties.

 

Let’s start by ruling out the most easily identifiable metal, copper. Copper is pretty easy to spot. It is shiny and copper colored when new, just like a new penny. It dulls and darkens to a brown color as it ages. Eventually it progresses to a green or greenish blue patina as it continues to weather. Regardless of exactly how old it is, copper tends to look nothing like the other “silver” metals used in roofing applications. Copper is also generally left uncoated so the color difference is easy to spot. Most people that opt for a copper roof are taking the patina into consideration as part of their choice and wouldn’t dream of coating it.

 

Now we can separate the ferrous metals from the non ferrous metals. The term ferrous refers to any metal with a primarily iron base. For our purposes that generally means steel. Most of your older roofs will be galvanized steel or Terne tin, which is also steel, despite the name. While the zinc coating used in the galvanizing process will not attract a magnet, the iron core material will. That means that a magnet will be the quickest and easiest way to determine whether the roof is steel. If a magnet sticks to the material then it is most likely galvanized steel or Terne tin. Stainless steel on the other hand is designed not to rust and the alloy metals added to the mixture generally prevent a magnet from sticking to it. Please note that some alloys of stainless steel will hold a magnet, but these types are not generally used in roofing panels.

 

Terne tin is a little trickier to determine. The term “tin” is a misnomer in this situation. It is very rare to find an actual tin roof. Generally, a tin roof is referring to one of two things. The first incarnation of the tin roof was a sheet of steel with a tin coating on the surface to prevent oxidization. The second incarnation is what we call Terne tin. This material still consists of a steel base, but it is coated with a Terne alloy in lieu of actual tin. Originally, tern was an alloy made from a blend of lead and tin. When lead was banned from use in construction Terne II was born. Terne II is an alloy made from a blend of zinc and tin.

 

As you can see, it can be difficult to determine whether a roof is galvanized steel or Terne tin without resorting to chemical tests. Fortunately, it doesn’t really matter. Both galvanized and Terne surfaces are prepared for paint the same way.

 

Let’s cover stainless steel now. Stainless is generally only used in commercial applications and even then it isn’t common due to the added expense. Stainless steel is naturally corrosion resistant, but it is still sometimes coated with an additional Terne II finish. The finish on stainless steel can be bright and shiny or matte depending on the product chosen. Generally, stainless steel is left uncoated and still retains a good appearance. There is really no need to paint stainless steel so it is one of the few roofing materials that will have a bright silver appearance. The Terne version will be harder to distinguish from normal Terne tin so a magnet will be needed.

 

Lastly, we’ll cover aluminum. Aluminum is more expense than steel and thus less common. It’s growing in popularity though because it is light weight, corrosion resistant, and dissipates heat quickly. A magnet will not stick to aluminum roofing material. Aluminum does not really corrode if left exposed, but it does discolor badly from the layer of protective oxidization that forms on its surface, making it an ugly natural finish. Most aluminum roofing will be coated, often coming from the factory in an assortment of colors. Sometimes it will also be anodized like the old paraplanes. Aluminum is very thin a flexible material and most often has a factory finish so it’s easy to spot.

 

Once the type of metal has been determined, you need to figure out what kind of coating if any is currently on it.

 

Traditionally, oil-based roof paints have been the most common product chosen. Most residential applications of any age will have at least one coat of oil on them and often dozens of coats will have built up over the years. Oil paints get brittle as they age and often start peeling as the number of coats increases over time. The paint film gets so hard and so thick that it eventually can’t keep up with the movement the metal experiences with temperature changes. When that happens the paint film starts to sheer from the metal and peeling results. These flakes of peeling paint will be very brittle and break easily, which makes spotting oil-based roof coatings fairly easy. If you can’t get peeling chips for some reason there is another way to tell if the roof has oil on it. Simply wet a rag with denatured alcohol and rub a spot with it. If little or no color comes off on the rag then you have oil paint. If the color does come off you have an acrylic paint. Alcohol is strong enough to melt acrylic products, but not strong enough to affect oil.

 

In more recent years acrylic DTM (direct to metal) products have become more common as a roof coating. Certain roofing materials, such as Terne tin and galvanized steel, accept waterborne coatings more readily than oil-based coatings. Acrylics are also more flexible than oil and thus handle movement in the metal better. They are also faster to dry, allowing a painter to turn a job around quicker. The speed of drying can pose its own problems though. DTMs are generally the product of choice for many factory finished metals. Peeling DTM will be flexible and rubbery. The color will also come off when applying the alcohol test.

 

Another less common roof coating is elastomeric paint. Elastomerics are also waterborne acrylics, but they have elastomeric resins built in as well. These products leave a much thicker and more rubbery film and generally only come in white. Even when a colored version is present they are easy enough to differentiate from a DTM. These coatings are mainly used in commercial or hospitality settings and are mainly used for their heat reflecting properties. This makes them more common in warmer areas such as Florida. Test for this product just like DTM, but pay attention to how thick and rubbery the film is and what color it is.

 

There is one other type of coating that is commonly found on buildings like barns or storage sheds. Asphalt roof coatings are sometimes used on these roofs because they are extremely cheap and are thick enough to fill pinholes in the metal. You have plain asphalt, fibered asphalt and fibered aluminum asphalt. Asphalt will be black and tarry. Fibered asphalt will look like normal asphalt but have more texture from the material fibers in it. The aluminum variety will look like fibered asphalt, but will have a dull aluminum color to it. All of these coatings are a real pain to deal with as far as recoating with other products.

 

Preparation

Bare Metal

Bare metal is the best substrate to work with in most cases. You don’t have the existing coating to deal with. Surface condition can be a factor though.

 

First let’s cover rust and corrosion on steel surfaces. If there is any rust or other corrosion that is loose and scaly it must absolutely be removed via mechanical methods. This can involve wire brushing, scraping, grinding, sanding, and other procedures such as sand or soda blasting. Remove as much rust and scale as possible. When you are left with just a residue you can choose to further treat the issue or to depend on the rust inhibitive properties of your coating system to put a “band-aid” on the problem.

 

It is recommended to further address the residual rust with a solution of phosphoric acid. Products such as Ospho are recommended for this. Ospho is a light phosphoric acid formulation. You simply pour it on the surface and brush it into place. Let it dry and repeat if rust is still apparent. Ospho will etch the surface of the metal and convert the iron oxide (rust) into iron phosphate, an inert substance that turns the metal black. Sweep away any powder left by the process and you are ready for primer and paint.

 

If no rust is present on the steel a simple pressure washing may be adequate to clean the surface of the roof. Be aware that a lack of rust indicates the presence of a coating such as zinc galvanizing or Terne. Galvanized or Terne surfaces must be etched with a product like Ospho to avoid adhesion problems with the coating system. When galvanizing or Terne is believed to be present, clean the roof via pressure washing and let dry. Then apply a coat of Ospho and let it dwell for 30 minutes. Rinse clean and allow the surface to dry completely before applying a coating system. You may allow the Ospho to dry and sweep it away in lieu of rinsing it if appearance is not as important. However, rinsing the surface will result in a smoother finish.

 

Let’s move on to aluminum. Aluminum should not form any major corrosion. A simple pressure washing is generally adequate preparation for an aluminum roof. If desired, the metal can be etched with Ospho just like steel. This will result in a better bond with the coating system. If scaling has formed for some reason handle the issue in much the same way as you would rust on a steel surface.

 

Next, we’ll cover stainless steel. You really shouldn’t paint stainless steel. It defeats the purpose of using it in the first place. When you absolutely must paint it, follow the preparation instructions for aluminum.

 

Finally, we’ll cover copper. Copper really should not be painted. It defeats the purpose of using it since copper can last centuries. It also takes away from the natural beauty of the metal. There is also the problem of keeping a coating on it. The chemical reaction that occurs when copper oxidizes burns off just about anything you put on it. So just leave copper alone.

 

Previous Coatings

Unfortunately, a painter is seldom blessed with the gift of a bare metal roof to work with. The great majority of the time the roof will have a previous coating on it. It could even have multiple coats present. Some old roofs have been found to have 30-40 layers of paint on them. When that much paint is present it may be time to replace the metal instead of painting it. Make sure you examine that option alongside the option of a proper repaint to determine which one is better in the long run.

 

If you have an oil coating on the surface in question, which is the most common situation, then you’ll want to remove any loose and peeling areas of paint via mechanical methods. This means scraping, sanding, wire brushing, and so on. Pressure washing will seldom remove all loose debris. Treat any rusting or corroding areas the same as you would if they were present on bare metal. If the majority of the coating is still sound you can get away with spot priming the bare areas you’ve exposed before applying paint. Otherwise, you’ll be best served by removing as much coating as possible before a full coating system of primer and paint is applied.  Once the loose material is removed, pressure wash the surface to remove any residual contamination.

 

Surfaces painted with an acrylic product can be prepared much the same way as a surface coated with an oil product. Just be very careful when removing the loose material. Acrylics tend to peel in strips and keep on peeling if they are not securely adhered, whereas oils break up more readily as they peel.

 

Surfaces painted with an asphalt product are often a lost cause. Asphalts are extremely difficult to coat over effectively and even more difficult to remove. Generally, anything coated with asphalt probably isn’t material of any quality and you’d be better off replacing it. If you must paint over it, remove anything loose via mechanical methods and give it a good pressure washing.

      

 

General Notes

There are a few final notes concerning preparation. It is recommended to use a detergent such as Jomax or TSP when cleaning and pressure washing a roof. Water alone will not always remove all of the contaminants. A detergent is essential to achieving an optimal surface. Once your surface is clean and ready for coating do not leave it for more than a day or two before applying the primer. The more time you allow the surface to remain exposed, the greater the chance it will become contaminated again.

 

A Note on Lead

If you have an older roof you should familiarize yourself with the hazards of lead. Many old roof coatings and Terne formulations used lead in the mix. When grinding or scraping where one of these coatings is present you are releasing lead dust into the environment. Breathing this dust can result in lead poisoning.

 

The EPA has spent the last few years cracking down on lead as well. It’s treated much like asbestos now and heavy fines can result if you make a mistake handling it. Consult the EPA website for more information.

 

Coating Systems

Now that your roof is prepared for paint you need to choose the correct coating system for the existing surface. There are three main types of roof coatings for general residential application. These include traditional oils, newer Acrylic DTMs, and Acrylic Elastomerics.

Types of Coatings

Traditional oil coatings are linseed based long oils designed to bond tightly to the metal and provide as much flexibility as an oil coating can. This is the type of coating that has been used for many decades and remains the most common product in use today. The biggest drawbacks to oil coatings include lack of colorfastness, brittleness with age, and long dry times. The longer dry times make for slower turnaround and require that care is given to the time of day you are painting. In spring and autumn weather, painting too late into the day with an oil product can make it susceptible to spotting from evening dew.

 

Acrylic DTMs are newer products that have come down from the industrial and railroad divisions. These products have been formulated to take the place of traditional oil coatings in a world that is constantly pushing for GREEN building initiatives. They are very durable, have better colorfastness than oils, better flexibility on metal surfaces, and have a faster turnaround time since they dry rapidly. The drawback to the rapid dry time is that you must be careful not to apply them in direct sunlight or on very hot days to avoid lapping and flash drying, which will result in a less than desirable appearance and possible adhesion issues.

 

Elastomerics are more of a specialized product. They are more commonly used in commercial and hospitality projects, but can be used quite successfully in a residential application. An elastomeric coating is a waterborne blend of acrylic and elastomeric resins. It is much thicker than a normal acrylic coating and provides a thick rubbery membrane when dry. These types of coatings are generally used in warmer climates such as Florida due to their ability to reflect heat and provide a little insulation from the sun.  They often contain ceramic micro-spheres to further promote heat reflection. Elastomerics are most readily available in white, which is also the best color to reflect heat. Other colors are sometimes available, usually on a special order basis, and more common in cooler climates like Canada. Elastomerics behave very much like acrylics with the exception of having a much lower spread rate due to the their thick viscosity. Their heat reflecting properties as well as the ability to fill small pinholes are their strongest advantages. However, most homeowner generally do not like the appearance of elastomeric coatings, especially when they are available only in white.

 

Choosing a Product

Which type of product to use depends largely on the surface you are coating as well as the intended application. Considering the focus of this article, we’ll assume the intended application is your standard residential roof. Therefore, we can focus on what the substrate calls for.

 

When to Use Oil

An oil system should be used when you have a very rusty ferrous metal surface that you do not intend to etch and convert with a product like Ospho. Oil roof primers and paints are naturally better at handling rust bleed through and reducing future oxidation of the metal.

 

Oil products should also be used when the existing coating is already an oil product, especially when multiple coats are present. If you have an old roof with existing oil paint on it you are better off recoating it with more oil unless you are willing to strip the roof to bare metal. Acrylic DTMs and Elastomerics have an aggressive bite and will often bond to old oil without an issue. However, the acrylic and oil products expand and contract and a much different rate. This usually results in the acrylic coating pulling the old oil coating loose, which will result in peeling. The top coat is only as good as what lies beneath it.

 

When to Use Acrylic DTM

Acrylic DTMs should be used on any surface that is not friendly to oil products. These include aluminum, galvanized, and Terne products. You will get a much better bond to the properly prepared surface of one of these metals from an acrylic than you will from an oil.

 

Acrylic DTMs should also be used when colorfastness and flexibility are a major concern. They will greatly outperform oil products on both accounts.

 

Acrylic DTMs are also the product of choice when trying to coat over old asphalt products. There is no guarantee in this situation that anything will really stay bonded to the old asphalt surface, but acrylics have a better chance of adhering than oils.

 

In general, any new surface should be properly prepared and coated with an Acrylic DTM unless the specific properties of an elastomeric are called for. Oil will eventually disappear under pressure from the EPA. There is no reason to coat a new surface with a dying technology and have to deal with conversion issues in the future.

 

When to Use Elastomerics

Elastomerics need little explanation. They are such specialized products that very few situations will call for them. They are primarily called for if you are specifically looking for their heat reflecting properties.

 

Application Dos & Don’ts

Generally, application of any of these systems will consist of applying one coat of rust inhibitive primer and two coats of finish with proper dry time between coats. It is important that the primer be rust inhibitive on ferrous surfaces. In the case of oil products you will most likely be looking at a red oxide metal primer. Acrylic DTMs are also available in a red oxide variety. Both types also commonly come in gray and sometimes white, but red oxide is preferred for the greatest rust inhibitive capability. Elastomeric coatings should be applied over a coat of red oxide acrylic DTM primer.

 

If you have a sound existing coating and are applying a coating of the same type of product over it, i.e. oil over oil, then fully priming the roof is not necessary. Spot prime any bare areas and then apply two coats of finish product over the entire roof.

 

Application via brush, roller, spray or a combination thereof is acceptable provided proper film build of each coat is achieved. Use a film gauge to check this if necessary.

 

Avoid applying a coating in direct sunlight, especially waterborne coatings. Also be sure to honor the approved range of temperatures for the product in question. Generally, surface temperatures should fall between 50 and 90 degrees Fahrenheit. Surface temperature refers to the temperature of the surface you are painting, not the ambient air temperature. A metal roof that has been in direct sunlight for a while can be much hotter than the air around it. Too hot of a surface can cause the solvents in a product to flash off too fast and prevent proper bonding. This can also result in visual defects such as dull and shiny spots and a crinkled film. Too cold of a surface can retard drying and curing of the product and also result in adhesion issues.

 

Avoid painting too early or too late into the day, especially in spring or autumn weather. Dew is often the culprit when visual problems occur on an exterior paint film. Painting a surface too early in the morning when the weather has been very cool does not give dew time to dissipate and can result in adhesion and blushing issues. Painting too late in the day allows dew to form before the paint film is dry and can also cause blushing.

 

Be careful to get good coverage on the seams of the roof. These are the most difficult areas to coat well when applying product with a roller or brush. The flat surfaces are much easier to achieve full coverage.

 

Refer to the documentation or sales representative of the specific product you choose to use for full recommended application procedures.

 

Application Tools

 

Conclusion

The proceeding information should make it clear that application method is only one small part of the equation when dealing with a metal roof. Properly identifying the existing surface and correctly preparing it for a coating are essential steps to achieving a good looking paint job that will last for many years.

 

The length of this article may make painting your roof seem like a formidable task, but be assured that it is not. There are simply numerous variables that need to be covered. Once you have identified the substrate and chosen a product to apply, you’ll always know the best system for future use. Then it all comes down to common sense and knowing how to use your painting equipment.

 

This article was written with an emphasis on identifying the surface to be painted, properly preparing it, and choosing which type of coating is best for your application. Application tips have been provided but application procedures have been kept to a minimum. Once you’ve chosen a brand and specific product for your job, it is best to adhere to the manufacturer’s recommended application procedures first and foremost.

 

I hope this information has been helpful to those of you about to tackle a roof painting project. Please feel free to comment with any questions or concerns. I’ll try to keep this article up to date with any new information that seems relevant.

 

Disclaimer

I have worked in retail and commercial sales of residential and industrial coatings for over a decade. I am not a chemist or a metallurgist, though I do frequently have input from the chemists and field representatives of the paint manufacturers with which I deal. My knowledge is based solely on my real life experience with the products and situations discussed above, not on any official training. Please use this information as a starting point for your project, but discuss the details with your local paint representatives before proceeding.

By Chad Simmons – Morris Paint & Floor Covering, Inc.

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Comments

    • Pete Jones
    • June 22, 2013
    Reply

    If I have an oil surface over tern, after prepping the rusted areas, can I paint over the oil base with acrylic?

    1. Reply

      I wouldn’t recommend it. Oil and acrylic expand and contract at different rates. Acrylic also has a very aggressive bite. In my experience applying and oil over an acrylic often results the the new coating pulling the old coating off the metal. The acrylic is more elastic and moves more than the oil and since it bonds so well it’ll rip it off the metal. This is especially true on surfaces like tern, where the oil only bonds so well to begin with. Stick with oil in this situation unless you intend to strip the paint down to bare metal on the entire roof.

    • Fred Jaques
    • May 20, 2014
    Reply

    Very informative article, thank you. In the Seattle area, it is hard to find pros who repaint metal roofs. All the roofing businesses want to do is selling you a new roof.
    My roof uses SNAP-LOC 0.018 inch thick steel panels, made by Champion Metal of Washington, Inc. It has been installed 16 years ago. The color is fading and the underlying zinc coating (G90) is showing up. It needs to be repainted. I don’t know the original paint, except it is “a 1 mil/two coat Baked-on finish”.
    The pitch of the roof is 1 in 5 and the surface is about 3,200 sq. feet.
    I have some questions:
    1. Can just the bare zinc areas be treated ?
    2. Can the old brick red color be matched?
    3. How long do you think this repair would last?
    4. Is acrylic DTM the correct paint to use?
    Thanks
    Fred

    1. Reply

      First things first. Have you contacted Champion? They supposedly put a 50 year warranty on this roofing. I’d find out exactly what is covered before incurring any cost of repairs yourself. To answer some of your questions:
      1) Yes just the bare areas could be coated. I’d mechanically abrade it and etch it with a phosphoric acid solution first. Then apply the spot primer and finish coats.
      2) Yes the color can be matched. However it may not match well enough to look good when spot painting, especially considering how long the surface has weathered.
      3) Longevity is very dependent on weather conditions. The coating will probably hold up well for several years. The color, being a field tinted red, would likely fade over the first few years. Reds and yellow do not hold up to sunlight well. That’s why most of these colors are factory mixed with industrial pigments. You may be able to find a dealer that has an industrial tinter and can give you better life expectancy out of the matched color.
      4) This is tricky. Normally I would say yes. The coating that is on your roof is Akzo Nobel Ceram-A-Star 950, which is an acrylic based system. However, it is also silicone modified. Silicone causes all kinds of issues because nothing else likes to stick to it. I’m not sure of what the exact silicone content is and whether it would cause adhesion issues. This link is to info on the Champion site. http://championmetal.com/metal-roofing-and-siding-resources.html You can find information there about repainting you product. They have recommended products that will be your safest bet. Of course you are getting into products that are not so commonly available. Therefore you will likely have to get them through Champion and pay a premium price for them.

      I would send all this to my manufacturer reps to get some info and recommendations for you, however the brand I carry for this is a regional company that will not be available in your area. If you want to stay away from the specialized Akzo product, I’d recommend a visit to Sherwin Williams or PPG. They have extensive industrial lines and should be able to get you in contact with their technical personnel that can make an informed recommendation on which of their products will work. If they won’t recommend anything for it, then you’ll likely be looking at acquiring the Akzo products.

      I hope this helps. Thanks for reading.

        • Fred Jaques
        • May 22, 2014
        Reply

        Thank you very much for your answers.

        Yes, I contacted Champion a few days ago. A secretary transferred me to a manager. He was absent, so I left a message. He never called back…

        To repaint the roof, the Champion web site lists an application guideline of an AkzoNobel VAOC31630 Gray Tiecoat, followed by an AkzoNobel CERAM-A-CRYL II top coat. They specify a 0.25 mil (!) application. Also, they don’t have a procedure for the subsequent application of the CERAM-A-CRYL II top coat.
        I will try to get this stuff, but it’s like pulling teeth.
        My problem is to find a competent roof painter who has done this rigmarole.

        1. Reply

          I’ve had a hard time trying to track down an MSDS for the product to even see what the silicone content is, if they even list it. I did finally track down a number for Akzo Nobel Technical, which also wasn’t easy. 1-800-294-3361. I’d see if they can give you any insight on where to get the product from. You may want to inquire about warranty as well. They rate the product at 30 years. In the past Akzo has always been good about providing product even if the problem was not their fault.

          As far as painters go, these look to be single component products that any decent painter could apply. The key is making sure they prep the surface correctly to avoid problems.

    • Traci
    • June 4, 2014
    Reply

    I was searching for field paint for a zincalume/galvalume roof and came across this thread. Did you ever find a solution, Fred? We live at the beach in a harsh environment (Los Angeles = salt, wind, fog, dew nightly, and POLLUTION) and our roof just looks old and drab. We want to paint it, if we can get 7-10 years out of it. I am meeting with a guy from Nu-Tech Paints tomorrow. They are based out of New Zealand or Australia and just started distributing in the US a few years ago. http://www.nutechpaintsca.com. This is a pretty new subject for roofers in general as there aren’t all that many metal roofs down here. It’s frustrating.

      • Fred Jaques
      • June 6, 2014
      Reply

      Thanks for the info, Traci.
      I have the same problems with my roof as you have, 11 miles South of Seattle. I also have a whole bunch of fir needles getting stuck in the metal ribs and they are very acidic.
      I found an outfit back East that does exactly the painting job I need, with the exact paint needed, see http://www.metalrecoaters.com/about.asp However, their web contact is broken and they don’t answer my faxes.
      I might try these Nutech people. But you are right, trying to have a metal roof repainted is very frustrating. Nether roofers nor painters know how to do it! I think that most people let their roof rust and put up a new roof.

    • Lea kasala
    • August 22, 2014
    Reply

    Used elastomeric on metal and it turned orange,like a speeded up rusting. I sanded them off again, but I’m left with what type of white paint i should coat it with before spray painting it.

    1. Reply

      Water based coatings can do that if not primed correctly. If it’s a ferrous metal surface, i.e. an iron based metal like steel, it needs to be primed with a rust inhibitive DTM primer after taking care of any scaling rust and converting any rust residue with phosphoric acid. Then you can apply a quality elastomeric coating over the DTM primer.

    • Mitch
    • May 29, 2015
    Reply

    Great and informative… The first article I have come along that really provides information and not trying to manipulate you into some sales pitch or just ends up being a bunch of crap… Also from the few things I knew everything seem to line up so it also gain confidence in the rest of the information provided.Nice job and thank you.

    • Scott
    • August 9, 2016
    Reply

    I had a 1922 standing seam terne metal roof with multiple peeling layers and have successfully removed all multiple prior coatings with a two step method:
    (1) a Wagner power steamer, model 705 bought for about $50 at Home Depot. Using the Steamer Plate in the kit laying on the roof for about 3-4 minutes it released the bond of 95 years of coating down to the 85% bare metal and 15% of the original first coating. Used a narrow paint scraper to remove the paint layers relatively easily (compared to other methods!) while I heated a section using the steam plate, moved the plate to the next section and scrape that previously heated section and repeat. Most of the bare metal was exposed on my roof using this method. There was still a small amount of bonding left from the first coating which on my roof was a linseed oil primer with a nicely faded thin oil top coat. The great thing about this steam method is you are not kicking up any dust whatsoever, and paint chips do no fly into the air. The moistened paint chips are easily cleaned up afterwards.
    (2) I coated the remaining original scraps of stuck paint left from the steaming method with Klean Strip Aircraft Stripper, lightly scraped again and was left with a smooth brand new looking terne metal surface to recoat ! Since there was only a small amount of the orignal coating left on the metal that stripper worked like a champ.

    The last coating i did was a Devoe Devguard 4308 Industrial alkyd coating with Devguard spot priming recommended by Devoe. It only lasted 2 years before turning from beautiful dark gloss hunter green to nasty flat weathered blue, and let me tell you, two years is not enough for all that prep work!! Planning on going with an Acrylic DTM for the color and gloss retention that Chad talked about in this article. Any suggestion on the best performing Acrylic DTM for long lasting glossy Hunter green pigment? Any idea how long the terne metal can be exposed to rain and wether before rusting starts?

    1. Reply

      Sounds like you did some real work on that one. Good job on prep. I use to sell Devoe product and while some of their products were good, they really don’t have anything specifically formulated for a roof. Was the Hunter Green tinted for you or did it come pre-packaged from the factory? If it was tinted for you, do you know if they used industrial pigments or standard pigments? All of this plays a factor. Factory tinted product uses industrial strength pigment, which will last longer in sun exposure. Store tinted usually uses standard pigment, which will fade quicker. It is possible to store tint with industrial pigment, but unless the shop specializes in industrial work they probably don’t have a machine setup with industrial pigments. These pigments dry out quickly and if you don’t tint from them often then end up being a huge waste of money. Oil paint also just fades and gets brittle on exteriors far faster than acrylics.

      As for product recommendation, it really depends on where you are at. I sell mostly Davis Paint Acrylic DTM, which comes in a selection of factory packaged roof colors. This product was originally developed by Davis Frost (Davis Paint’s parent company) for recoating old rail cars. It was originally spray only, but has been reformulated for brush and roller and introduced to their standard industrial line. It’s a very tough and proven product. Davis is a small regional company out of Lynchburg, VA though so availability is not that great if you are not on the mid-east coast. I know a very successful product for this type of application is Sherwin Williams Sher-cryl. This should be available nationwide. It is a system though, requiring a certain method of prep, primer, and top-coat. It’s also way overpriced in my opinion. I’d recommend you talk to a local SW rep about the product if you are interested in using it. The other brand I carry is Pratt & Lambert, which is a sub-brand of Sherwin Williams. They have never had a strong industrial line that I would recommend anything from for this application. P&L has recently dropped their entire industrial line and taken on the Krylon Industrial line, which is also a sub-brand of Sherwin Williams. This has been very recent and I have no experience with this new product line yet, so I can’t make any recommendations there. My experience with other brands is limited and well out of date at this point. Products have certainly changed a lot since I carried anything else. PPG and Muralo would probably be other good lines to look at with a proven track record for industrial finishes. I’d stay away from Duron as that was bought up by Sherwin Williams some time ago and they are gradually reducing that company to a shell before it disappears completely.

    • Jeanie Osburn
    • October 1, 2016
    Reply

    We have a Follansbee Terne II metal roof which we had installed in 1994. We’ve painted it twice since the original coat. The last time we painted was in 2008 and our powerwashing basically took off all the original Calbar paint. We coated it with Follansbee’s Rapid-Dri primer followed by 3 coats of their Rapid-Dri stainless steel fleck top coat. It’s time for us to paint the roof again (it’s been 8 years), however, to my dismay, Follansbee is out of business, and I can’t get their paint. We don’t have much peeling. Just a couple of places. What brand of paint would you recommend? We had really good luck with the Follansbee paint, and would like something that works as well.

    1. Reply

      Jeanie,
      This is a tricky situation. My supplier has run into this coating before and most products seem to have issues bonding to it due to the stainless steel fleck. I’ve got my manufacturer checking with their technical department to see if there is a product recommendation for anything in their line. I’ll get back to you as soon as I get a solid answer.

      1. Reply

        Jeanie,
        At this point, I’ve contacted multiple suppliers and gotten zero good information. None of them are willing to spec a coating system for this. They all seem to think there is going to be some major issue with it, but no one is willing to tell me exactly why. I can only assume the existing coating is known to be difficult to recoat and the manufacturers are shying from it to avoid liability. Sorry I couldn’t be more help on this one. I’ve contacted Davis Frost, Sherwin Williams, Devoe, and PPG with no luck. There may be other more specialized brands available in your area that would be worth checking into.

    • JACK SORENSEN
    • October 30, 2016
    Reply

    Good article – what type paint should be used over asphalt coating if any left after pressure washing? Thanks

    1. Reply

      Generally Acrylic paints will bond better over residual Asphalt coatings than oil based products will. A good DTM would be the best choice.

    • Joe
    • November 3, 2016
    Reply

    Thanks so much for this piece. I have 100 year old row house in Washington DC. I was trying to learn what coating to use on the 20 year old flat seam metal roof of my front porch. When that replacement roof was new it had an oil paint on it and instinctively painted it 10 years ago with oil but did no research on prep. I will soon paint it again with oil based paint and good preparation per your piece…..and I will have much more than “instinct” to guide me. The in-depth information you provide gives me confidence that I am spending my time and money well as I ready this good house for its next 100 years and owners who recognize good stewardship of this property.

    1. Reply

      I’m glad you find the information useful. Good luck with your project.

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