Overview

Hot-air welding is what makes a TPO roofing system watertight. When done correctly, a robotic heat welder creates seams that are stronger than the membrane itself. When done incorrectly, seams fail — and a flat roof with failed seams will leak. At Trust Roofing, operating the robotic heat welder correctly is a required skill. This training covers how to set up, run, and inspect a robotic hot-air welder for consistent, code-compliant TPO seam welds.

Our Field Standards

Robotic TPO welding follows Trust Roofing field standards.

Field standards include:
* The welder is warmed up and test welds are performed before any production welding begins
* Weld temperature and speed are confirmed on a test seam before proceeding
* The welder tracks along the seam without deviation — straight, consistent passes only
* Weld width meets or exceeds the minimum specification — typically 1.5 inches
* Every seam is probed after welding to confirm bond strength — no exceptions
* Any failed or questionable seam is re-welded before moving to the next seam

Our Process

Setting Up the Welder

* Allow the welder to reach operating temperature — typically 15 minutes
* Perform a test weld on a scrap piece of TPO membrane
* Check the weld width, bond strength, and appearance of the test weld
* Adjust temperature and speed as needed

Understanding Temperature and Speed

Temperature and speed work together:
* Too fast or too cold: under-welded seam — will peel open during probing
* Too slow or too hot: over-welded seam — membrane may wrinkle or burn through
* Correct combination: weld edge shows a slight bead of melted material

Running the Welder

1. Align the welder nozzle precisely at the seam overlap edge
2. Start the welder and allow it to build momentum
3. Maintain a straight, consistent pass — do not wander from the seam line
4. Keep the following distance consistent — do not stop mid-seam if possible
5. Complete each pass to the end of the seam before stopping

Post-Weld Inspection

After each seam:
* Allow the weld to cool — typically 3 to 5 minutes
* Probe the full length with a probe tool
* Any area that lifts during probing is a failed seam — mark and re-weld
* Document seams that required re-welding

Roofing Terms

Hot-Air Welding

The process of fusing two TPO membrane surfaces together using a stream of heated air, melts the thermoplastic material at the interface and creates a molecular bond stronger than the membrane itself when performed correctly.

Weld String

The thin bead of melted material that appears at the leading edge of a properly welded TPO seam, indicates that sufficient heat and pressure have been applied to create a complete fusion bond through the full seam width.

Probe Tool

A small blunt-tipped metal tool used to test TPO weld strength by inserting the tip into the seam edge, a properly welded seam resists penetration; a failed or cold seam allows the probe to slide in easily.

Florida TPO Product Approval

Florida Building Commission product approvals for TPO membrane systems specify minimum weld widths, fastener patterns, and installation procedures, deviation from approved methods voids the system’s Florida approval.

Cold Seam

A TPO weld that appears visually complete on the surface but has not achieved full molecular fusion due to insufficient heat, speed, or roller pressure, identifiable only through probing and a common cause of flat roof leaks in Florida.

Related Topics