Recoating a Metal Roof | Metal Construction News (2022)

By Mark Robins Senior Editor Posted September 01, 2021

Recoating a Metal Roof | Metal Construction News (1)

One of metal roofs’ best benefits is their longevity. Metal roof panels have baked-on OEM coatings or finishes for aesthetic or functional reasons. But these coatings may deteriorate, become damaged or fade over time, possibly leading to building leaks, corrosion and energy efficiency problems. The good news is recoating metal roofs with a variety of special materials means the entire roof doesn’t need to be scrapped and replaced.

Gary Edgar, national coil and extrusion specification manager at Pittsburgh-based PPG Industries Inc., explains roofs are recoated before the intended service life expediency for three primary reasons: aesthetics and color, mechanical and storm damage, as well as environmental conditions that cause corrosion and premature failure, especially without a regular cleaning routine. “In terms of color and aesthetics, roofs are typically recoated because the owner, corporation or school decides the roof color is no longer current. Mechanical and storm damage can fracture the coating film and system, leading to premature failure and usually includes damage during the original installation and installation of new equipment on an existing roof. Hail and flying debris can also fracture the coating system, and if left unchecked, can lead to delamination of the coating system. A harsh or aggressive environment will attack a coating system much faster than a mild environment, thus requiring more cleaning to keep the corrosion and chemical attacks at bay. The coating system will begin to fail if a proper maintenance routine is not in place in these environments.”

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Doug Loomis, vice president of Energy Coating Systems Inc. (ECS) of Conroe, Texas, says, “We are always first and foremost called because of leaks and/or rust, mostly on roofs 20-30 years old and some earlier. Generally, leaks and rust always start with the fasteners. A properly applied high-grade coating system that addresses these problems can turn the any roof into a sustainable roof.”

Recoating a metal roof is typically a fraction of the cost of a complete roof replacement. Roof coatings can be applied in half the time of a new roof installation and they reduce the disruption of building tenants.

Coating Application

There are many ways to apply coatings to metal roofs, the most common being spray application and roller application. The best method for a particular project will be determined by the specific conditions presented, including slope, panel profile and coating type.

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“Spray application requires heavy-duty, professional-grade spray rigs designed and intended for roof coatings,” says Jeremy Grunewald, product category manager—liquid-applied systems, Mule-Hide Products Co. Inc., Beloit, Wis. “These spray rigs typically have higher output and pressure capabilities at the pump than you’ll find with a traditional paint or coating sprayer that can be found at a big-box retail or DIY store: 4,500 psi or 7,250 psi compared to less than 2,000 psi. The higher pressures and outputs allow for greater production efficiencies and faster application speeds, which are critical factors for contractors.”

Jeff Stephens, brand manager at Rust-Oleum, Vernon Hills, Ill., agrees the vast majority of metal roof restorations are applied using roofing spray rigs designed for roof coatings. “The airless spray rigs allow for a much more uniform application of product at specified coverage rates over irregular panel surfaces in addition to increased productivity.”

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Grunewald explains roller application may require paint rollers, brooms, brushes, squeegees or other manual application tools. “The type of coating, application rate and desired finish of the coating will determine the appropriate roller nap thickness—i.e., 1.25-inch nap or 1.5-inch nap—and roller head material type: synthetic fibers or foam.”

Contrasting the two application techniques, Edgar explains an airless spray application resembles the original factory application, while roll application typically has a slight texture, which may or may not be acceptable to the owner.

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Ed Buczek, senior product manager at The Garland Co., Cleveland, contends airless spray equipment is very useful for covering the underside of metal roof vertical seams. “That detail is difficult to do well with rollers and brushes. Spraying a metal roof is usually quicker than roller application and coverage rate more controlled. However, there are tank spreaders for metal roof application now available that can rival the speed and effectiveness of spraying without overspray concerns and spray equipment cleaning/maintenance.”

Recoating Errors

Inadequate surface preparation and improper identification of the existing coating or substrate are common mistakes when recoating metal roofs. The long-term performance of coatings in metal roof restoration depends on the coating’s ability to tightly adhere to the metal roofing surface.

“Inadequate surface preparation can leave behind dirt, debris, grease, oil or loose rust, which can reduce the coating’s ability to adhere to the metal roof,” says Grunewald. “Over time, a poorly adhered coating may begin to peel, crack or blister, causing not only unsightly aesthetic concerns, but also creating the potential for water to penetrate between and underneath the coating and the metal roof. This can, of course, result in roof leaks or cause the coating to further crack, blister or peel. Improper identification of the existing coating on the metal roof may also lead to similar coating adhesion concerns due to inadequate bonding between the new coating material and the existing coating.”

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Stephens contends 90% of all metal roof recoating failures are due to inadequate surface preparation, and that properly preparing corrosion areas and in some cases, priming is a must. “The project always needs to address the cause of leaks and the details of the restoration which vary project to project. Once all flashing and detailing conditions are completed, the coating restoration will have a higher success ratio compared to just applying a restoration coating.”

Edgar agrees that improper metal roof surface preparation and wrong product recommendations are common mistakes when it comes to recoating metal roofs. “Mock-ups are a great way to ensure proper adhesion and owner satisfaction.” Buczek says a common recoating mistake is poor flashing detailing, specifically at horizontal panel overlaps and any internal drains. “It’s imperative to provide fabric reinforcement and high-performance sealers in these areas of greatest strain on a metal roof where a coating alone will eventually fail.”

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Loomis says he has seen many poorly applied coating applications over the years and that it always boils down to poor quality workmanship. “Pay attention to the details and the outcome will be as expected. I have seen as many metal roofs installed improperly as coating systems. The outcome is always the same: failure to live up to desired results and an unhappy customer. No matter what roof or coating system you are installing, follow manufacturers’ recommendations and pay attention to details.”

Correct Recoating Material

Selecting and using the correct material is imperative for recoating roofing. Stephens contends not all roof coatings are right for every roofing type. “Silicone roof coatings tend to have low corrosion protection. Contractors and building owners should look at coating metal roofs with aluminum, urethane and some elastomeric roof coatings to deliver long-term performance. Rust-Oleum has developed a Premium Elastomeric 880 that is a single component, rust preventive, water-based acrylic elastomeric roof coating. The self-priming, high build coating is designed for use on tightly adhered rusted surfaces or clean steel. The excellent elongation properties of over 500% make it suitable for bridging small cracks.”

Grunewald explains roof coating span a wide variety of technologies and chemistries from water-based to solvent-based technologies and moisture-cured to evaporative-cure chemistries. “For most common applications of roof coatings, there may be differences in procedures such as surface preparation or the use of a primer. We recommend that the manufacturer’s installation instructions, procedures and specifications be followed whenever applying a roof coating.”

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Over the past few decades, there has been a large shift and trend in the commercial roofing market toward white, reflective, cool roof coatings. “The roof plays a critical role in the transmission of heat into a building, thanks to its size and direct exposure to the sun,” Grunewald says. “The heat from the sun raises the roof’s surface temperature, and that heat then transfers to the building’s interior. This then puts greater demand on HVAC units to maintain hospitable conditions in the occupant spaces. White, cool roof coatings have high reflectivity and emissivity, meaning they keep the rooftop cooler and then expel much of the heat that does enter the building.”

Edgar explains these reflective coatings are becoming more mainstream, “Especially with the environmental focus on carbon footprint and saving energy. These pigments show real value with darker colors, whereas lighter colors reflect heat more naturally.”

Loomis notes all coatings are climate sensitive and that there are temperature ranges and rain chances to consider. “Yes, many regions have adopted requirements for a certain energy-saving quality to their roof surface. Any white paint/coating will have a reflective quality, but the greatest advantage is in the emissivity quality of most coatings. Important to metal roofs is the reduction in thermal shock.”

Grunewald says that like many building and construction materials right now, costs and lead times for metal roofing systems have gone up significantly in recent months. However, “Coating systems for fluid-applied roof restoration and recoating are currently providing lower costs and significantly faster lead times. If a property manager hasn’t considered recoating their roof as a restoration option, now may be the optimal time.”

FAQs

How long does a coating last on a metal roof? ›

How often? Field-applied coatings are typically re-coated anywhere from five to 12 years after installation.

What kind of coating can you put in a metal roof? ›

How to Apply Metal Roof Coatings | GAF Roof Mate - YouTube

How thick should roof coating be? ›

The thickness of the coating can vary when performing a seam reinforcement, but it's usually 20-30 mils of coating.

How many times can you recoat a roof? ›

How Often Do Roofs Need Recoating? Typically, a built-up roof will need routine maintenance and re-coating every 4-6 years. Ponding areas may need more frequent re-coating. Built-up roofs should be checked at least once a year for developing issues.

Can you recoat a metal roof? ›

The good news is recoating metal roofs with a variety of special materials means the entire roof doesn't need to be scrapped and replaced.

What is the longest lasting roof coating? ›

Spray Foam Roofing (SPF Roofing)

Sprayed Polyurethane Foam, also known as SPF, is regarded among the longest lasting types of roofing systems. Many SPF roofing systems have endured for over 50 years with few signs of failing.

What is the best roof sealer for metal roof? ›

For a metal roof system, a silicone sealant is preferred as it adheres well to metal and other common construction material. It also offers excellent moisture and UV protection and features exceptional joint movement capabilities.

What roof coating is best? ›

Polyurethane coatings provide the best rates of all coatings for impact resistance and for foot traffic. There are two types of polyurethane roof coatings: aromatic and aliphatic. These types of materials are typically used in combination of base coat and topcoat.

How long do the rubber washers last on a metal roof? ›

3. The metal panel may last 50 years but the rubber washer keeping the water out will only last 9-15 years. Metal has the highest expansion and contraction factor of any other roofing product on the market.

How long will a 29 gauge metal roof last? ›

Longevity. Metal roofs can last 40-70 years, depending on the material.

How long will a 26 gauge metal roof last? ›

Other benefits of standing seam and metal roofs include: Durability — Unlike other roofing materials, standing seam roofs use 26- or 24-gauge metal which does not crack or corrode. Many standing seam roofs can withstand winds up to 140 mph and can last 50 or more years. They quickly shed ice, snow and rain.

How often should you paint a metal roof? ›

Metal roofs can fade over time, especially due to the elements like harsh sunlight and heavy rains. Whether you want to change the color or restore the same one is up to you. It is recommended to repaint about every 10 years.

What is the longest lasting roof coating? ›

Spray Foam Roofing (SPF Roofing)

Sprayed Polyurethane Foam, also known as SPF, is regarded among the longest lasting types of roofing systems. Many SPF roofing systems have endured for over 50 years with few signs of failing.

Is roof coating any good? ›

Its major strength is that it offers an incredible balance of cost and performance. Acrylic roof coatings are also highly reflective, UV-resistant, and easy to work with, making it a popular choice for many.

Do roof coatings work? ›

Coatings may be an unnecessary expense: Coatings are often considered an economical way of increasing a roof's reflectivity to reduce cooling costs. However, a coating is not always necessary if enough insulation is installed – which negates the need for any thermal coating to help cool a roof in hot climates.

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