As they age, coated metal building products can take on a lackluster appearance. Time and environmental conditions take their toll, and the coating degrades, exposing the underlying substrate to damage. In this situation, architects may be tempted to replace facade materials with new, factory-fresh materials—a costly, time-consuming endeavor that disrupts building occupants and activities and diverts old materials to landfill.
A better option is freshening a building’s exterior with field-applied coatings optimized for metal surfaces. The right exterior coating can provide the same type of fade-resistant performance associated with its factory-applied counterparts.
Choose the right coating system
Careful selection of the right coating system and attention to proper surface preparation can make the difference between a long-lasting finish and one that fails in several years.
Architects have moved away from “off-the-shelf” paint to engineered coating systems formulated to bond to metal substrates. Compatibility among system components—primer and topcoat—and the engineering behind the formulation will help ensure against coating adhesion failure and extend the lifetime of the protective coating. It is important to specify a primer and topcoat system from a single manufacturer as they will be specifically formulated and tested for compatibility and inter-coat adhesion. Poor inter-coat adhesion can allow moisture to get in between the primer and the topcoat, leading to blistering or delamination.
While topcoats may get more attention from a curb-appeal standpoint, the quality and performance of a coating system’s primer can make all the difference. Primers fill the pores of the surfaces being coated and increase the adhesion of the coating. A primer coat helps to seal the surface, hide stains, prevent bleed-through, and create a neutral base for any coating color. If the primer formulation is not engineered for the specific surface substrate—a formulation developed for masonry is not suited for steel surfaces—or environmental conditions, pre-existing issues are likely to progress after refinishing. Further, the same building material may require different primers based on pre-existing conditions, such as the substrate’s age, type and condition of existing coatings, and the environmental factors the coating will be exposed to after the installation, such as salt and water migration or abrasion.
At tough, durable finish
For decades, architects have trusted the long-term, fade-resistant performance of exterior metal building products coated with polyvinylidene fluoride (PVDF) based finishes. These finishes are baked onto products like aluminum doors and window frames at the factory.
Today, architects and specifiers can take advantage of water-based, field-applied coatings with PVDF resin. These coatings have consistently demonstrated an ability to resist fading (Delta E < 5) for 15 years or more in high UV settings like southern Florida.
PVDF’s incredibly strong carbon-fluorine bonds stand up to film erosion, even under exposure to the elements, allowing its protective properties to last significantly longer. The figure below shows the extent to which UV energy breaks down common coating binders, reducing their mechanical protection properties. Also, PVDF resin has very minimal absorption of UV energy, making it ideal for coating applications needing strong UV resistance.
Crucial surface preparation
The process of applying a protective coating to metal exteriors is more complicated than it might seem—if it is done right. Simply pressure-washing the facade and then painting is not nearly enough.
A careful pre-job inspection should be conducted to assess surface conditions and identify environmental contaminants that need to be removed. Before applying the primer, all areas should be examined for pre-existing coating defects such as holidays, crazing, cracking, blisters, efflorescence, blushing, and chalking, as well as surface or substrate defects such as improperly welded areas, mold growth, and corrosion. Proper mitigation should be taken to resolve all issues using The Society for Protective Coatings (SSPC), National Association of Corrosion Engineers (NACE) or the International Organization Standardization (ISO) standards. Surfaces should undergo thorough cleaning using methods such as blasting, power tools, or hand tools, in addition to solvent wipe cleaning. This process aims to eliminate all contaminants, including chlorides, sulfates, nitrates, oil, grease, soil, dust, and mill scale. The Field Coatings Guide, technical data sheet, and specification document from the coating manufacturer provide additional guidance on surface preparation.
A coating’s curing ability, lay down/aesthetics, and dry film thickness (DFT) are impacted by the building’s micro-climate. Coatings applied in poor environmental conditions can risk the long-term performance of the coating and negatively impact its lifecycle. Application will run more smoothly and lead to better results if the coating system has early water resistance and the ability to be applied in a range of temperature and humidity conditions.
Installation mock-ups can help to ensure issues are addressed before they become costly mistakes requiring re-work. Ultimately, a thorough pre-job assessment and selecting a knowledgeable coatings contractor that works directly with the manufacturer, issues should be minimal to nonexistent.
Ernie Porco is a product application engineer at APV Engineered Coatings. He is the subject matter expert for the Neverfade Facade Restoration Coatings with Kynar Aquatec product line, along with the original equipment manufacturer- (OEM-) applied coating products.
