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72 SEPTEMBER 2015 COATINGSPROMAG.COM Science Behind It A Specially Designed Polyurethane System By Adriaan van der Capellen, West Coat Rep for Polycoat USA T he underground parking garage at the Camelot Apartments was constructed before the coating contractor arrived on site. It was created using precast planks, which is a work of art in itself, over which a topping slab was poured. Te topping slab had numerous issues. Te concrete was severely cracked — hairline and larger cracking — all over the place. On top of that, it had a bad fnish that was really rough. It was also leaking into the next level of parking below. W hen the coating crew started to prep the garage with shot blasters, a standard method of surface prep, the process started to blow up the concrete and expose even more cracks. Tose results made it clear that the crew couldn't just apply a typical vehicular coating system to the deck. Instead, they would need to come up with a solution to repair the concrete prior to application of a vehicular deck coating system. Te team came up with a hybrid solution that would mitigate the various problems. Creating a System Because of the existing condition of the garage slab, the concrete wouldn't accept a standard polyurethane deck coating system. Tose typical systems can only be applied at certain thicknesses or they' ll blister, outgas, and pinhole, and this garage needed more than a typical deck coating system. To deal with these conditions, the team decided to use a polyurethane deck coating system consisting of a chemi- cally cured basecoat that can be applied at any thickness without blistering followed by the application of a standard moisture-cured polyurethane intermediate and topcoat. Te system included the main workhorse, PC-260 from Polycoat, which is an elastomeric base membrane. It is a solvent-free, high-solids, two-component polyurethane coating that's fast curing and can be applied at any rate to achieve desired thick- ness. Because the team knew that the coating would puddle in areas due to the unevenness of the slab, this polyurethane membrane was chosen because it doesn't blister. However, the polyurethane basecoat couldn't be used alone. As a rule, polyurethane coatings do not bond to concrete without a primer. Te primer used was Polyprime 21, which is an epoxy polyamine primer with a high solids content. It has unique penetrating characteristics that penetrated and sealed all of the garage's cracks. Essentially, the primer penetrates and bonds to the concrete; the basecoat then bonds to the primer. Tis was followed by the application of moisture-cured polyurethane intermediate and top coats. Te cracks were, of course, repaired by indus- try standard crack repair methods involving striping cracks less than 1/16th inch (1.6 mm) in width with basecoat and grinding or routing cracks over 1/16th inch (1.6 mm) to a ¼- by ¼-inch (6.4 mm x 6.4 mm) width and caulking with a polyurethane sealant. Because the polyurethane intermediate and top coats alone are as slick as a skating rink when wet, aggregate must be broadcast into the intermediate coat for non-skid. Te intermediate coat and topcoat were Poly-I-Gard 246, which is a polyurethane coating; it's a standard coating for vehicular deck systems. Tis Poly-I-Gard 246 has important physical characteristics, such as hardness, tensile strength, elonga- tion, and tear resistance, that allow it to be subjected to vehicular trafc. Te Pol-I-Gard 246 was applied to the entire deck and broadcast with sand; it was applied again to the high-wear areas (e.g., turning areas and drive lanes) and again broad- cast with sand. It was then applied to the entire deck without sand as the fnal topcoat. Te use of the coating with the aggregate helped to create an anti-skid and wear surface that can also be cleaned easily of all parking-related grimes, including oils and fuels. Parking Schooled W hen that whole system was complete, what was left was a waterproof vehicular trafc deck coating system with an aggregate wear system and a fve-year warranty. By combin- ing the strength of the polyurethane coating along with the primer and the protection of the topcoat and aggregate, this parking garage was set for success. CP