Understanding today’s coatings for claddings

All photos courtesy Sto Corp.

by Ed Telson
Even those best-designed, well-constructed buildings degrade if the appropriate exterior coating and finishes are not applied and maintained in a timely manner—this is especially true for demanding environments. Fortunately, there is a wide-ranging array of high-performance architectural coatings available today that can not only safeguard a building’s value, but also create dramatic visual appeal.

It is important to differentiate in the architectural world between the terms, ‘paints’ and ‘coatings.’ The definitions can often blur and be confusing, especially as the industry continues to evolve. The term ‘paint’ can refer to any coating, but is more typically marketed for aesthetics and the general DIY market. The term ‘coating’—especially those deemed ‘functional’ or ‘protective’—applies to products that have likely been tested to meet independent, and often higher, standards. (A third term, ‘finishes,’ should not be confused with paints or coatings, even though all three are often incorrectly treated as being interchangeable. Solids make up the bulk of finish products, and they are applied with a trowel in contrast to coatings and paints that rely on spray units, rollers, and brushes. Some finishes may offer protection from the elements depending on build and quality, while others may be purely decorative.)

Conventional exterior paints do not usually have the same protective qualities as coatings; rather, they are typically more prone to soiling over time and incur mildew and algae caused by weather and wind drift. Ultraviolet (UV) rays from the sun may further accelerate the deterioration of paint. Coatings, on the other hand, are typically specified as a prescriptive system with reference to millage build and application steps designed to achieve a higher level of performance than mere paint. The difference between paints and coatings can be seen in product data sheets, which list test and performance data.

Higher millage, balanced with superior resin performance, can be used as another way to characterize the difference between paints and protective and functional coating systems. When comparing millage, acrylic paints are typically applied in a dry film thickness (DFT) of 0.06 to 0.08 mm (2.5 to 3.5 mils) and contain solids in the 35 to 40 percent range. In other words, 60 to 65 percent of the solvent used to apply the product evaporates.

Architectural protective and functional coatings can range from 53 to 70 percent solids, or even higher. This leaves a DFT between 0.25 and 0.8 mm (10 and 30 mils) on the surface, with only 30 to 47 percent of the product evaporating. In this way, the millage specified by the manufacturer in product data sheets provides an indication of the optimal performance standard for a given protective architectural coating system. With a higher percentage of solids, such coatings offer both decorative and protective characteristics. The industry trend has been to utilize these higher-build acrylics on claddings and substrates for a longer cycle and protection.

Coatings come in a wide variety of choices ranging in quality and system capability—from providing more decorative, short-term benefits to superior protection and durability. Again, an evaluation of product specifications and testing data is the best indicator of probable performance of a coating product and system. Building owners seeking maximum protection for a façade should assess its condition and need for repair before carefully evaluating the available coating solutions.

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