TechNews: Thermoplastic Welding Tips

Versico recommends the following best practices to reduce cold welds and help ensure the watertight integrity of TPO, PVC, and KEE HP single-ply roof systems.

1. Equipment
Use proper power sources or commercial-grade generators. Generators should be rated for 3,000 watts for two hand welders, or 6,500 watts for one auto-welder. Proper extension cords are critical. For auto-welders, use a 10-gauge wire with a maximum length of 100 feet; for hand welders, use a 12-gauge wire with a maximum length of 100 feet. Welders should be in good shape, with clean air screens and a clean nozzle.

2. Temperatures
The following are starting guidelines for temperature, speed, and airflow. Settings may vary depending on membrane thickness (45-, 50-, 60-, or 80-mil). Check out Versico’s TPO and PVC/KEE HP welding guides for more information.

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TPO Welding Guide 
PVC/KEE HP Welding Guide 

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3. Critical Welding Steps
Keep in mind that ambient temperatures will affect welding temperatures and speeds, as will welding in the sun versus welding in the shade. Certain substrates can hold heat in the membrane (polyiso insulation), while others can rob the heat from the membrane (concrete). When hand welding, immediately roll across the hot seam at a 45° angle with a 2” silicone roller. This helps to ensure the top membrane is adequately pressed into the bottom membrane. When welding across a step-off, be sure to crease the top membrane into the step-off with a 2” silicone roller immediately after welding. This will help prevent a water channel from forming in the weld. It’s important to perform test welds several times each day because of changing ambient and membrane temperatures. Simply cut a 1”-wide strip across the weld and peel to inspect the weld area. Remember to probe all seams at the end of each work day. Tip: Avoid using the edge of the roller, which can damage or cause cold welds on TPO/PVC.

4. Cleaning and Maintenance
Always clean aged or dirty membrane before welding. On PVC or KEE HP, use PVC and KEE HP Membrane Cleaner; on TPO, use Weathered Membrane Cleaner. Clean all residue from the weld area and allow it to dry before welding. Maintain your equipment before, during, and after welding. Regularly inspect the silicone pressure wheels on your auto-welder and hand roller to make sure they’re not affecting the integrity of the membrane while welding or rolling. Clean the char off the heat gun nozzle using a brass wire brush and keep the intake free of debris to allow maximum airflow. On the auto-welder, adjust the nozzle to eliminate heel drag.

Following these helpful hints will ensure a better installation with fewer cold welds. If you have questions, check out Versico’s TPO and PVC/KEE HP Welding Guides or contact your Field Service Representative.