The Midwest Roofing Contractors Association (MRCA) has a reputation for top-notch technical sessions, and its 2010 annual conference in Indianapolis was no exception. A standing-room-only crowd was on hand for the panel on “TPO Long-Term Performance.” 

The Midwest Roofing Contractors Association (MRCA) has a reputation for top-notch technical sessions, and its 2010 annual conference in Indianapolis was no exception. A standing-room-only crowd was on hand for the panel on “TPO Long-Term Performance.” Moderated by MRCA’s technical advisor, Rene Dupuis of SRI Consultants Inc., the panel featured Helene Hardy Pierce of GAF Materials Corp., Dwayne Wacenske of Firestone Building Products, Tom Taylor of GAF Materials Corp., and Randall Ober of Carlisle SynTec.

Wacenske concluded the panel discussion by examining installation practices that affect the performance of both TPO and PVC. “Installation practices affect the long-term performance of the roofing system,” he said. “Initially the roof may be fine, but some problems can arise years later.”

Hot-air welding of the seams was identified as the most common source of trouble. Wacenske recommended that test welds be done at least twice daily - at the start of the day and after lunch - and whenever the machine is restarted. The most common problem was excessive heat during welding, which can consume polymer stabilizers. Excess heat can result from the air temperature being too high as well as the welder speed being too low. Wacenske noted the ideal welding temperature should be the lowest temperature that provides good seams at production speeds.

Another common problem is welder drag. “Improper alignment of the hot-air nozzle can create gouges in the membrane outside of the seam,” said Wacenske. “The inside edge of the nozzle should be aligned with the edge of the roller.”

Probing seams can also lead to problems. “Be careful probing seams,” he said. “Use a blunt probe. Probes sharpen with use and occasionally must be dulled.” He urged contractors to keep the tip of the probe horizontal to avoid causing damage.

Creasing the membrane when it is folded during installation is another installation error that can lead to problems down the road. “Folding over the membrane can result in a hard crease and surface cracking,” he explained. “Membrane can be folded back for applying adhesives or fasteners, but weight should not be placed on the fold to hold it in place.”

The panel’s entire PowerPoint presentation is available at www.mrca.org.