Approved gas protection installers do some of the most important work on any development, and most of it disappears under concrete within days. The quality is usually excellent. But in my experience carrying out verification visits, it's rare to leave site without finding at least one thing that needs attention.
That isn't a reflection on the installer. More often than not, it's what happens around them.
The site doesn't stand still
An installer can leave a membrane in perfect condition at 3pm, and by the next morning it has been walked on by steel fixers, had rebar chairs pushed through it, or had a new service duct added that wasn't on the drawings. Weather, programme pressure and other trades all take their toll.
Those issues can't be blamed on the installer, but if they're buried under the slab, the installer's name is still on the job.
Why sampling isn't enough
Partial verification assumes problems are spread evenly across the area. In reality, they tend to appear in a few specific places:
- Service penetrations added or moved after installation
- Laps disturbed by foot traffic or weather
- Corners, steps and junctions with walls and cavity trays
- Damage from following trades
- Venting layers crushed or blocked
Checking only part of the area risks missing the one detail that matters.
Verification works in the installer's favour
Full, independent verification gives approved installers:
- Evidence that their work was right at handover
- Protection if damage occurs after they've left the area
- A clear record, with photos tied to each plot and location
- The chance to put things right before the pour, when it's quick and cheap
It turns "we did a good job" into "here's the proof we did a good job."
Supporting the design
Standards such as BS 8485 and CIRIA C735 place real value on independent verification because the design assumes a continuous, well-installed system. Verifying all of it gives everyone, from designer to client to installer, confidence that the system will perform as intended.
Working together
The best results I see come from installers and verifiers working as a team: coordinating around the programme, flagging late changes, and signing off each area before the pour. Approved installers already hold themselves to high standards. 100% verification simply makes sure those standards are still intact when the concrete arrives.
Installers, what's the most common issue you come back to find after other trades have been through? I'd be keen to hear your experiences.