December 5, 2019
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Seam probing is an important final step in the hot air welding process because it is a good indicator to determine if proper fusion has occurred between the membrane layers. Whether the membrane is TPO or PVC, both products need to be probed – but with slightly different techniques.
Probing must be done once hot air welds have thoroughly cooled (at least 20 minutes). Premature probing can damage warm seams. Hot air welded seams must be probed throughout the day to check seam quality and to make proper adjustments to hot air welding equipment. The repair of deficiencies must be done routinely throughout the day, but no later than the end of each workday.
A blunt or dull cotter pin puller is an acceptable tool to perform the probing task. Versico offers a custom-designed Seam Probe that incorporates an ergonomic, threaded handle with a heat-treated, plated steel tip. With continued use these tools will wear down, creating a tip that is too sharp for probing. Blunting the tip is necessary when this occurs.
When a substantial amount of probing is necessary, an extension pole can be threaded into the handle of the Versico probe. This allows the operator to stand up while probing long runs of field seams.
Draw your 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 welded overlap area, use a water-soluble marker to mark 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. Versico recommends that repairs be made the same day deficiencies 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. Another reason all laps must be probed each day soon after they have cooled is 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.
Considerations when probing TPO systems
1.) TPO does not "flow" like PVC. If you observe an area in which you see "flow" of the bottom ply, scorched areas of detail/flashing membrane, or scorched field membrane welds, these areas should be probed. If these areas are overheated to the point of membrane damage, an overlay repair will be required even if the weld probes successfully.
2.) A properly heated field membrane weld will typically have a visual "sheen" approximately 1/2" wide on the bottom sheet at the weld overlap. When walking seams, look for the sheen. If it is not present, probe to ensure weld quality.
3.) TPO seams require a minimum 1.5" weld. Welds less than 1.5" must be overlaid as stated in Versico’s specifications and details, even if probing does not produce deficiencies.
Considerations when probing PVC systems
1.) Welds on PVC systems should produce "bleed out". Bleed out refers to the flow of the bottom ply (of the top sheet) outside of the weld. If you do not see bleed out at seam areas, this increases the probability the seam did not receive enough heat when it was welded. Be sure to probe these areas to ensure weld quality.
2.) PVC is a “softer” and more flexible membrane than TPO. As such, a different probe should be used than the one used on TPO roofing systems. The PVC probe should have a blunt/dull tip, or utilize a "hook" screwdriver with a flat head.
3.) PVC seams require a minimum 1.5" weld. If you observe welds which are less than 1.5", these should be overlaid following specifications and details, even if probing does not produce deficiencies.
Remember, application of Cut Edge Sealant should not begin until all probing is completed.
Please contact Jim Gage with questions.
Senior Technical Specialist