Seam Probe

A seam probe is a simple hand tool used to check the seams of single-ply roof membranes for gaps, voids and unbonded sections. It typically has a handle and a slender metal shaft ending in a blunt, slightly hooked or rounded tip. The tip is drawn along the outer edge of a lap with light pressure; where the seam is properly fused or bonded the tip slides along the edge, but where there is a void it catches and enters the seam.

Where it is used

• Thermoplastic membranes (TPO and PVC) joined by hot-air welding. Membrane manufacturers' guidance calls for all seams to be probed, typically at the end of each work day once they have cooled.
• EPDM seams joined with tape or adhesive, to check edges for lifting.
• Flashings, patches and details where hand welding is more prone to gaps.
• Inspection of existing roofs during maintenance surveys and leak investigations.

Technique

Seams must be allowed to cool fully before probing, since warm thermoplastic can be pushed open by the tool and give a false failure, or seal over a void. The inspector runs the probe along the entire length of each seam, paying special attention to T-joints (where three layers meet), step-offs, corners and around penetrations, which are the most common locations for voids. Defects found are marked with a crayon or marker and repaired, usually by re-welding or by welding a patch over the area, followed by probing again.

Limits

Probing checks only the leading edge of a seam. A seam can be intact at the edge but poorly fused behind it, which is why manufacturers also call for test welds and peel tests during installation. Probing also cannot find punctures in the field of the membrane; electronic leak detection and visual inspection address those. A probe with a sharp point can damage membranes, so dedicated seam probes are designed with rounded tips.

Related tools

Hot-air welders, silicone seam rollers, and peel-test cutters make up the basic seam quality-control kit on thermoplastic roofs.