Wet Film Thickness (WFT) Explained

Fire Resistance Is Thickness-Dependent

Fire resistance ratings — such as 30, 60 or 90 minutes — are achieved through independent laboratory testing of intumescent coating systems applied at specific thicknesses. These tests establish how long coated steel remains below its critical failure temperature during a fire.

The specified WFT for a 30-minute rating is fundamentally different from that required for 60 or 90 minutes. If the coating is under-applied, the steel will heat faster than the tested system allows. Over-application can also create defects, cracking or adhesion issues. Fire performance is only achieved when coatings are applied exactly to the tested specification.

Immediate, In-Process Measurement

WFT is measured immediately after application using calibrated wet film gauges. Measurements are taken while the coating is still wet, allowing adjustments to be made in real time to ensure compliance before curing begins.

This approach ensures consistency across complex steel profiles and prevents compliance issues being discovered after curing.

Why WFT Logging Matters

Every WFT measurement is recorded and cross-referenced to the project specification. These records form a critical part of the fire-protection compliance pack.

WFT documentation provides clear, auditable evidence that the installed system matches the fire-rated design.

WFT measurement and verification are non-negotiable in compliant fire protection. Accurate thickness control, environmental monitoring and structured records are what separate verified fire performance from unproven application. This level of control can only be delivered by trained, competent contractors operating within defined quality systems.

We prioritise wet film thickness control, environmental logging, product traceability and layer-by-layer inspection throughout application. Comprehensive documentation ensures building control approval, insurance acceptance and assured project sign-off.