Parking Lot Flooring: Epoxy or Polyurethane?

Multiple shopping mall construction projects are underway across the country, while renovation and improvement work continues in many existing malls. Since most mall customers generally arrive by vehicle and enter via the parking facilities, parking lot design is gaining increasing importance. In shopping mall parking lots with heavy vehicle traffic, implementing a polymer coating system that is both aesthetic, has high scratch resistance, and can provide long-term service requires attention to several factors. When the time comes to decide what type of coating should be applied to a parking lot floor, the choice between epoxy or polyurethane coating systems can always be somewhat troublesome. Indeed, when research is conducted and the resulting information is analysed, the process of deciding on the correct coating system can be somewhat challenging. Epoxy and polyurethane floor coatings protect concrete floors from stains, damage, chemicals, oils and, perhaps most importantly, wear and tear damage. Both systems are light-reflecting, provide a bright space, are easy to clean and long-lasting. They also have their own specific advantages depending on the application. So which should you use and what is the difference between them?

Advantages of Epoxy Floor Coatings

Epoxy is a thermoset polymer; three different formulations can be used for parking lot floor coating: water-based, solvent-based and 100% solids. With these formulations, coatings of varying thicknesses can be applied; with paint application a dry film thickness of 400-800 microns can be achieved, while with coating application a film thickness of 1.5-3.0 mm can be obtained. The application characteristics of the systems, their inherent adhesion properties and VOC considerations can be important decision factors in some cases. Epoxy adheres extremely well to a properly prepared concrete surface. Because of this property, it is also used as a surface repair and preparation material prior to applying polymer coatings to old and worn concrete floors. The best epoxy formulations are those containing 100% solids; these products provide an extremely hard, durable, thick and impact-resistant surface. These self-levelling epoxies fill small capillary cracks and defects in the floor due to their thickness, and also contribute by protecting the concrete floor. At the same time they have high resistance to surface sticking/peeling caused by hot tyres, scratching and wear. Although UV inhibitors have been added to some epoxy formulations to increase UV resistance, yellowing will occur with prolonged exposure to sunlight. This can be an important consideration when deciding on a parking lot floor coating.

Advantages of Polyurethane Floor Coatings

Polyurethane, like epoxy, is a thermoset polymer and polyurethanes are considered high-performance coatings. Generally known by the shorter name urethane, this is technically incorrect; there is a significant difference between polyurethane and urethane. All coatings published as urethane coating are actually polyurethane coatings. Polyurethane coatings have higher flexibility than epoxy coatings and this flexibility dampens impacts. Additionally, due to the topcoat applied over it, wear resistance is also high. Compared to epoxy coating, polyurethane coating's wear resistance is almost 3 times higher. In some cases, polyurethane's chemical resistance can be higher than epoxies; it has high solvent resistance. For example, its resistance to methylene chloride, the main chemical in paint strippers, is very high. Another advantage of polyurethane over epoxy is that it is UV stable. This property means that there will be no yellowing if exposed to low levels of UV rays for extended periods. The surface of polyurethane is not as hard as epoxy, but polyurethane's scratch resistance is much higher. It also tolerates temperature differences much better and produces excellent results when used in wet areas. Although polyurethane systems have many advantages over epoxy systems, they do not adhere well to concrete, so polyurethane coating is applied after an epoxy primer application to ensure the system is solid and durable. In the application of polyurethane systems, as with epoxy coatings, the concrete surface is mechanically abraded to prepare the surface, followed by epoxy primer application. Polyurethane is used in the layer called striping or intermediate coat, and after self-levelling polyurethane coating is applied over this layer, the coating is finished with an aliphatic topcoat.

When polyurethane is a self-levelling system like epoxy coating, small cracks and damage on the surface are sealed in the same way as with epoxy.

In polyurethane self-levelling materials containing 100% solids, VOC is zero; by using water-based topcoat polyurethanes instead of solvent-containing topcoats, the total VOC values of the system can be kept below limits. Although epoxies are a leading coating system in many industries due to their high load-bearing capacity and resistance to corrosive chemicals, when considering loads and chemicals in parking lot floors, both epoxy and polyurethane can be used as parking lot floor coating systems. The additional properties of polyurethane are characteristics that are important in parking lot floors. Due to polyurethane's elasticity, cracks that may occur in the concrete floor as a result of building movements will be tolerated by the elastic coating applied over it. The coating forms a "crack bridge" over these cracks, preventing water penetration into the concrete floor. In epoxy coatings, water that can penetrate concrete in this way eventually creates negative water pressure, which causes epoxy coatings to lift from the floor. Additionally, water passing through these cracks in the floor can penetrate to the lower levels of the parking lot. This water generally dissolves minerals and salts in the concrete and can drip onto vehicles located in the lower level, damaging their paintwork. Furthermore, polyurethane paint applied as a topcoat has very high friction resistance. For this reason, a parking lot floor coating with polyurethane can successfully serve for many years despite heavy vehicle traffic. An aliphatic polyurethane topcoat will not yellow like epoxies, so it will maintain the colour and vibrancy it had on the day of application. Although a polyurethane system with many additional properties has a slightly higher cost per square metre than epoxies, this difference is not as high as might be thought. When a price/performance comparison is made of these two products, this modest price difference will be seen to be small, and in fact over the long term, due to the longer coating renewal frequency in polyurethane floors, it will be seen to be economical for operations. Saydun Gökşin / General Manager - PÜRKAY Boya ve Kimya San. A.Ş.