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48 MARCH 2016 COATINGSPROMAG.COM Science Behind It The Black Magic Science of Polyurea By Dudley J Primeaux II, PCS, CCI, VersaFlex Incorporated I t is often thought or presented that "polyurea" coating projects are just that: polyurea projects. And not much is given as to why a specifc polyurea system was used and the resulting overall performance. So what makes a good polyurea job or project? Well, it is not the polyurea by itself, but the actual system that was used. Te success in this Water FX application is from following the science of proper application and installation work, which come from having proper training and qualifcations. Over the past 30 years, I've heard that "urethane chemistry," which incorporates polyureas, is a type of black magic science. The Illusive Primer Chemistry In selecting the primer system, the system supplier should consider compatibility issues, environmental issues, and substrate characteristics. For concrete, we know that the surface w ill be weak ( low tensile strength), w ill be porous, and w ill have some moisture content. Selection of a primer system should be based upon the chemistr y of the appli- cation project, including project exposure, environmental issues during installation work, and the recoat w indow of the primer system. For this Water FX work, the VersaFlex VF 20 primer was specified. T his is a 100 percent solids, urethane-based primer system that remains ver y f lexible after cure. In addition to the 100 percent solids characteristics, the primer is based upon renewable resource polyols, which allows for relative cure insensitivity to residual moisture and high alkalinity of the concrete substrate. T his means that the minor residual moisture in the concrete does not interfere or obstruct the reaction or the primer system. Additionally, the high alkalinity of the concrete has no effect on the formed poly mer of the primer system. In addition, the VF 20 primer has been show n to signifi- cantly reduce the Moisture Vapor Emission (MVE) rate in the concrete, as per ASTM F 1869: Standard Test Method for Measuring Moisture Vapor Emission R ate of Concrete Subf loor Using A nhydrous Calcium Chloride. The Performance Polyurea Basecoat Te fact that there may be movement, cracks, and the aesthetic nature of the concrete work, the next layer of the polyurea system — VersaFlex FSS 45DC — was chosen. Te FSS 45DC is a 100 percent solids, plural-component, aromat- ic-based polyurea elastomer system. Te chemistry of this layer includes matched materials viscosities of the isocyanate and resin sides (the components in the plural-component system) and slightly slower (aka longer) gel. A little longer gel time (~12 seconds) allows for several chemical aspects to take place between this coat and the previously applied primer: excellent wet out of the system, enhanced adhesion from the mechanical aspect, and increased chemical bonding. After it has gelled, the basecoat ofers several benefcial chemical aspects as well. First, it ofers a typical 400–450 percent elongation. It also maintains a Shore D Hardness of 45–50, which means that it is able to withstand 15 seconds of an indenter and maintain its shape. (For reference, a truck tire may have a Shore D of 50 where a hard hat has a Shore D of 75.) Te installed cured system also has excellent crack bridging capabilities. Even for the higher tensile strength of the FSS 45DC (about 2,500 psi, or 17.3 MPa), this elasto- mer passes ASTM C 1305: Standard Test Method for Crack Bridging Ability of Liquid-Applied Waterproofng Membrane for crack bridging of an existing crack of >1 inch (3.2 mm) at -20º C (-4º F). The Chemistry Magic of the Topcoat Given that the basecoat is an aromatic polyurea system, which will show surface degradation and color change when exposed to sunlight over time, the aliphatic polyurea system is then required as a topcoat. For this, Water FX used the VersaFlex GelFlex 1115 system. Tis is the beauty in the black magic science of polyurea. Te GelFlex 1115 is a plural-component, 100 percent solids aliphatic polyurea. It is a 1:1 by volume product that is designed to process using the same equipment as was used for the basecoat, in this case the FSS 45DC. Te topcoat product has good balance between elongation, tensile strength, and hardness, like the basecoat, and it also provides for an 85+ 60º gloss of the surface. Tis is possible due to the unique chemistry crosslinking that occurs and an even slower gel time (~1 min) of the system. A ll of those qualities allow the GelFlex 1115 to chemi- cally interact with the FSS 45DC basecoat, such that excellent chemical bonding occurs, creating a durable system. Multiple-Step Science It is not a single-reaction process but a multi-step interaction that provides for this type of success story. By using three coatings that interact together and form a system, Water FX was able to use the black magic of the polyurea technology. CP