A hot-air weld is either fused or it is only touching.

A TPO roof is a field of sheets joined by melting their surfaces together. The membrane itself rarely fails in the middle of a sheet. The seam is the system, and unlike the membrane the seam is not supplied by a manufacturer — it is made on the roof, on the day, in whatever conditions that day provided.

Compare this on your roof

A low-slope commercial roof at dusk, mechanical curbs silhouetted against a warm horizon.

At a glance

The system, before the sales pitch.

Specification first. Every row below is a property of the system, not a claim about a product line.

The weld is made, not delivered: Hot air softens both surfaces and pressure fuses them into one material. A correct weld is stronger than the sheet either side of it. Everything about quality control on a TPO project is therefore about the process rather than about the material that arrived on the truck.
Three variables, and they move through the day: Heat, speed and pressure. A robotic welder is set for the membrane thickness, the ambient temperature, the wind and the surface condition. All four change between early morning and mid-afternoon, which is why settings correct at eight are checked again later rather than assumed to hold.
A cold weld is indistinguishable by eye: A seam that is stuck rather than fused looks exactly like a sound one and will pass any visual walk. That single fact is the reason testing exists, and it is why a photograph of a tidy-looking seam proves nothing at all about whether it will hold.

A wide low-slope commercial roof running to a distant edge, mechanical units punctuating the field.

How the system behaves

Performance is an assembly, not a product name.

A domed rooflight on a raised kerb in a white single-ply membrane roof, welded seams running across the field around it.

Probe testing the whole length

A rounded seam probe run along the edge of every completed seam, with enough pressure to find an unfused section and not enough to open a sound one. It is done over the full length rather than on a sample, and it is a normal part of the working day rather than an inspection event that happens at the end.

Test welds and destructive samples

A sample weld run at the start of a shift and pulled apart by hand: a sound weld tears the membrane rather than separating at the seam. On larger projects, samples cut from the finished roof are pulled the same way and the openings patched. Both produce a dated result that goes in the file.

What ends up in the record

Welder settings and the conditions they were set for, who probed which areas and when, the shift test-weld results, and the location of every destructive cut with its repair. That is the difference between a warranty document and evidence that the roof was built the way the warranty assumes.

Choose a starting point

Match the next step to the condition.

A short, non-diagnostic guide for working out what kind of assessment conversation to prepare for.

What best describes the property today?

Decision support

Choose a starting point.

Four situations, and the sensible next move for each. It does not diagnose a roof, decide insurance coverage, or stand in for somebody looking at the property.

What the next step actually is
What to have ready before anyone arrives
What we will not ask you to do

Questions

Useful answers, without overpromising.

Can a TPO seam be repaired?

Yes, with compatible material, proper cleaning and preparation, and a weld made to the same standard as the original. The constraint is usually the age and surface condition of the existing membrane rather than the repair itself.

Why does the weather stop the work?

Because the weld depends on the surface. Dew, moisture, dust and a cold substrate all interfere with fusion, and a seam welded onto a damp or dirty surface is the classic cold weld. Waiting for the roof to dry is not a delay, it is part of the method.

Can seams be welded on an old TPO roof?

Sometimes, and it has to be established rather than assumed. Weathered membrane loses weldability at the surface, so it needs cleaning and often priming, and beyond a certain point it will not take a reliable weld at all. That test comes before a repair is quoted, not after it has failed.

Can I ask to see the testing?

Yes, and it should not come as a surprise request. Probing is part of the working day rather than an event at the end, so what you are really asking for is the record: the shift test-weld results, who probed which areas and when, and the location of every destructive cut with its repair. That set is the difference between a warranty document and evidence the roof was built the way the warranty assumes.

Assessment request

Tell us what is happening at the property.

Short, routing-only questions. Nothing here asks you to diagnose the roof yourself.