Can a leak survey tell if moisture inside a wall cavity is old or active?

Full transcript

George and Dave in conversation. Every word of the episode, exactly as recorded.

George

Welcome back. I'm here with Dave from ADI Leak Detection, the UK's leading leak detection specialists, who's here to answer your questions and provide expert leak detection advice. Dave, today's question comes from a homeowner who's just opened up a wall cavity during a renovation and found it's wet inside. They want to know, can a leak detection survey actually tell them whether that moisture is from an active leak right now, or whether it's historic? Water that got in at some point in the past and just never dried out.

Dave

That's a really important distinction to make, and yes, a leak detection survey can absolutely determine that. The two scenarios, active water ingress versus residual historic moisture, behave very differently, and we have specific methods that separate them.

George

So what are you actually looking for? Because from the outside, wet plasterboard is wet plasterboard, isn't it?

Dave

It looks the same, but the instruments tell a different story. The first thing ADI's engineers do is take moisture readings across the cavity using a calibrated moisture meter. Historic dampness tends to show a fairly uniform moisture pattern, it's spread out, it's settled. Active water ingress shows a gradient. You'll see higher readings close to the source and lower readings as you move away from it, because the water is still travelling.

George

So the shape of the wet patch matters, not just whether it's wet.

Dave

Exactly. And we pair that moisture mapping with thermal imaging. A thermal imaging camera detects temperature differences in the wall surfaces caused by evaporation. Active leaks produce evaporative cooling, you'll see a cold signature on the thermal image that tracks the path of escaping water. Historic moisture that isn't being fed by anything doesn't produce that same dynamic cooling pattern. It's a much flatter thermal picture.

George

That's clever. So thermal imaging is showing you movement, not just presence.

Dave

That's the right way to think about it. Thermal imaging traces active water movement through a structure. But we don't stop there, because thermal imaging has limits, particularly in cavity walls where there's insulation, or where the leak is very slow. That's where pressure testing comes in.

George

Walk me through that. What does pressure testing actually confirm?

Dave

Pressure testing isolates a section of pipework and applies a controlled pressure to it. If that pressure holds steady, the pipe is intact, which strongly supports the historic moisture conclusion. If the pressure drops, there's an active breach somewhere in that pipe, and water has been or still is escaping. Pressure testing on the supply or the heating circuit gives you a definitive yes or no on whether a pipe is currently leaking.

George

And what about situations where the pipe might be under a solid floor or behind a finished surface? Can you still locate where the breach actually is?

Dave

That's where tracer gas comes in. ADI's engineers use tracer gas to find the precise location of a breach when it's hidden. A safe, inert gas mixture is introduced into the pipe, and it escapes from the breach point and rises through the floor or substrate. A sensitive detector at the surface picks up where the gas is surfacing, and that pinpoints the leak location without the need to open up the whole floor.

George

So by the end of a survey, you'd genuinely know whether this homeowner needs to find and fix a leak, or whether they just need to dry the cavity out and carry on with the renovation?

Dave

That's the goal, and it's almost always achievable. Moisture measurement, thermal imaging, pressure testing, together those methods give ADI's engineers enough evidence to say: this moisture is being actively fed by a pipe breach, here's approximately where it is; or, this moisture is historic, the source has stopped, and you don't have an ongoing leak. Both answers are valuable, because acting on the wrong assumption costs a homeowner a lot.

George

I can see why that clarity matters so much before you start making decisions about remediation.

Dave

It does. If you rip out and dry everything on the assumption it's historic, and there's actually still a pipe losing water behind it, you'll be doing it all again in six months. Getting the determination right first is what protects the property and the renovation budget.

George

Dave, that's been genuinely useful, thank you. And if you're dealing with this kind of uncertainty during a renovation, ADI Leak Detection are among the most experienced water leak detection specialists in the UK, and well worth getting in touch with before you make any decisions about that wall cavity. Thanks for listening.

How this episode was made. This episode was produced using AI-generated voices and script, based on real leak detection questions and the working knowledge of ADI Leak Detection engineers.