Apex technical guide
Intumescent coatings for structural steel
An introduction to passive fire-protection coatings, specification control, film thickness and why traceable application records matter.
Published by Apex Specialist Spray Coatings LTD · Updated 2026-08-31 · Our experience and preparation standards
What an intumescent coating does
An intumescent coating is part of a specified passive fire-protection system. When exposed to heat it expands to form an insulating char that helps delay the steel reaching a critical temperature.
The specification controls the work
Required protection depends on the steel section, exposure, design temperature, fire-resistance period and tested coating system. The product and dry-film thickness must come from the project specification rather than a general allowance.
Preparation and compatibility
The steel condition and existing primer are checked before application. Primers, intumescent layers and decorative top seals must be compatible components of the approved system.
- Record environmental conditions
- Control wet and dry film thickness
- Observe recoat and curing periods
- Maintain batch and application records
Inspection and handover
Film readings and records are reviewed against the specification, with defects corrected before the final compatible finish is applied. A clear handover provides traceability for the completed passive fire-protection work.
