TecTopics: Focus on Test Welds and Seam Probing

March 27, 2023
When installing thermoplastic membranes, test welds and seam probing are essential to ensuring watertight seams and a roofing system that will provide long-term protection. For more detailed information about heat welding equipment and procedures, check out Spec Supplement T-01-23.

Test Welds
  • At a minimum, Carlisle recommends performing a test weld prior to beginning work each morning and afternoon.
  • The test sample should be approximately 1"-wide and longer than the width of the seam (cut across the heat welded seam).
  • Peel the test sample apart after it has thoroughly cooled (approximately 10 minutes) and examine for a consistent 1½"-wide minimum weld. Delamination of the membrane from the scrim reinforcement is an indication of a properly welded seam.
  • Discolored or scorched membrane – Increase speed setting if membrane discolors.
  • Voids and wrinkles – A properly welded seam should be free of voids and wrinkles and must be at least 1½"-wide.
Seam Probing
  • The use of a Carlisle Seam Probe is recommended to probe all heat-welded seams. Probing seams must be done once heat welds have thoroughly cooled. Heat welded seams must be probed throughout the day to check seam quality and to make proper adjustments to heat welding equipment. The repair of deficiencies must be done routinely throughout the day but no later than the end of each workday.
  • Prior to probing, allow heat-welded seams to cool thoroughly for a minimum of 30 minutes. Premature probing can damage warm seams.
  • Draw probing tool tip along the edge of the heat welded seam. Apply firm pressure to probe the seam junction, but not into the bottom membrane sheet. The tool will not penetrate into the lap area of a properly welded seam.
  • If the seam-probing tool penetrates into the lap area, mark the seam using a water-soluble marker at the beginning and the end of voids or wrinkles in the seam edge.
  • Repair seam deficiencies as soon as possible using the hand-held welder. Carlisle recommends that repairs be made the same day they are discovered.
  • Probe repaired seams after they have cooled completely. If the repair is acceptable, wipe off the water-soluble marker lines; if not acceptable, repair the seam using standard heat welded overlay procedures.
  • Note: All laps must be probed each day soon after they have cooled to verify the welder set-up is effective. Particular attention must be given to all membrane intersections and heat-welded seams at insulation joints. In addition, there should be periodic checks (including at the start of each day) to verify good peel strength.
For more information, check out our TPO and PVC/KEE HP Welding Guides.
TPO Welding Guide
PVC/KEE HP Welding Guide

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