Polyurea Coatings for Rehabilitation of Metal Roofing

High-build multi-component polyurea-hybrid spray-on coatings can provide the capability to quickly and cost-effectively rehabilitate metal roofs in lieu of more costly and disruptive roof replacement.  The multi-component coating can be sprayed onto a deteriorated coated metal roof surface, with minimal surface preparation.  An Army Installation barracks aluminum alloy roof was chosen for coating application. The barracks were occupied during the rehabilitation process, necessitating careful planning and monitoring of changes in the weather, especially the wind and rain.  The very fast set up time and the potential for overspray to fall on nearby vehicles and personnel also proved to be a significant challenge.  Over a three day period, the 20,000 square-foot roof was primed with two-component water based epoxy using a conventional airless spray system, and then top-coated.  The topcoat, a copper colored polyurea-hybrid roof elastomer, was applied using a two-component proportioner system and a spray gun with a No.2 spray tip at 1,200 psi back pressure.  The coatings required a heated fluid line for both components to reduce the viscosity for spraying.  The setup time of the coating material was several seconds; it was dry to touch in 45 seconds, and easily handled within several minutes.  The final thickness of the coating system was 40 mils.  The short setup and cure times were necessary to prevent runs and sags in the coating normally experienced when spraying high-build coatings on a sloped roof, especially during inclement weather.  Because of the heated lines and fast setup times, the polyurea materials can be effectively sprayed in cold weather whereas conventional coatings cannot.  The polyurea-hybrid coating can be expected to extend the service life of the metal roof by providing a very tough moisture impermeable spray-on membrane, which effectively seals surface defects, even around penetrations, pinholes and seams.