Thermoplastic polyolefin (TPO) is the fastest-growing segment of the commercial roofing industry. These membranes are used for mechanically attached, adhered, and induction welded roofing systems.
Manufacturers continue to work on improving the formulations of their products for the best possible performance in our industry. Still, the essential component of TPO's long-term performance is proper TPO installation techniques by Roofing Contractors. Manufacturers identified hot-air welding of the seams as the practice where the most significant mistakes were being made by contractors that can lead to substantial problems as severe as roof failures years down the line.
Below are some guidelines and tips from manufacturers, contractors, and my observations over the years to ensure a successful and long-performing installation.
Using adequately sized and maintained generators with a minimum of 10k watt output is essential for the performance of your automated welder. No other equipment, such as screw guns, hand welders, etc., should use that generator for a power source. Your extension cord should be a 12-gauge minimum to meet the requirements of the welder.
Test welds should be done twice daily, at a minimum, at the start of the day and after the crew's lunch break. It would be best if you also did test welds whenever the machine is restarted or if you have concerns about the integrity of the weld. You want to avoid both excessive heat and also too-cold of welding temperatures. Extreme heat destroys the polymer stabilizers in the TPO and leads to premature membrane deterioration. Too cold of a welding temperature leads to false welds. This condition appears welded when probed, but then alter pulls apart at the welded seam causing water infiltration into the system and building. Test welds will ensure proper welding temperature and speed throughout your installation. The welding temperature should be the lowest possible to provide good seams at the machine's set production speeds.
Welder drag is a condition caused by improper alignment of the nozzle's inside edge with the roller's edge. If this is not done correctly, improper alignment of the hot-air nozzle creates gouges in the membrane outside of the seam. This condition is the second most common cause of premature membrane deterioration.
The weld must be allowed to cool before being probed. Seam probing for checking seam quality is one of the misused techniques to assure maximum performance. I have seen this done incorrectly by installers and specifiers, third-party quality control personnel, and, yes, even manufacturer inspectors. When probing, your tool should be blunt and not sharpened to a point. Blunt probes can become pointed from general use and should be checked to verify that they are not too sharp before use. An overly sharp probe will unnecessarily dig into the membrane, causing damage. It is essential when probing seams to use caution because incorrect probing can lead to problems down the line.
Hand-welding should only be done when you can't run an automated welder. Hand welders need to be dialed in the same as the automatic units. Remember that the membrane will withstand higher temperatures, but items like prefabricated corners, boots, and T-patches will only tolerate lower temperatures.
All hand welds should be done in two passes.
· The first pass creates the air dam and preheats the membrane
· On the second pass, both the welder and roller are to be perpendicular to each other at a 45-degree angle as it passes along the seam.
Membrane Age and Cleaning
Your goal is to complete all welding before the end of each workday, but most projects will require some additional welding after the initial day of installation. For example, patches over punctures or additional penetrations being added. Use TPO cleaners and allow the solvent to flash off before welding.
Following these guidelines for hot air welding, referring to the membrane manufacturer's specification manuals, and always incorporating internal quality control measures in your installations will give you a quality and long-lasting roof every time.