Fire-resistant coatings and boards on steel structures provide years of protection, but are not an "apply and forget" solution. Weather influences, mechanical damage, and aging can gradually diminish their effectiveness.
In this guide you will read which types of fire-resistant coatings exist, what determines their service life, how an inspection with thickness measurement works and how to have damage repaired correctly.
What types of fire-resistant coatings are there?
- Intumescent coatings, also called fire-resistant paint. A relatively thin layer that swells in heat into an insulating layer. There are water-based, solvent-based and epoxy-based variants.
- Cementitious and fibre-based sprayed coatings. Thicker layers that insulate the steel without swelling, mainly used where the steel stays out of sight.
- Board cladding. Fire-resistant boards around the profile. Not a coating, but often included in the same maintenance plan.
A coating system has a fixed build-up: a primer suited to the system, the fire-resistant layer in the calculated thickness and, where necessary, a topcoat. That build-up has been assessed as a whole. Anyone who replaces one layer with a product the manufacturer does not specify as compatible falls outside the assessed application.
Indoors or outdoors: the environment determines the system
Fire-resistant coatings are assessed on the environment in which they may be used. The European assessment distinguishes four types:
| Type | Suitable for |
|---|---|
| X | All environments, including fully outdoors |
| Y | Indoors and semi-exposed, such as an open car park: frost, but no rain and little sunlight |
| Z1 | Indoors, including at high humidity |
| Z2 | Indoors, at normal humidity |
A coating intended for dry indoor spaces ages faster in an unheated, damp room or on an open parking deck. An inspection should therefore also ask whether the environment still suits the system used, for example after a change of use of the space.
How long does a fire-resistant coating last?
There is no fixed service life. A properly applied coating that suits its environment can last a long time in a dry indoor space. European assessments assume a working life for testing purposes, but that is no guarantee and no expiry date: what matters is whether the system still suits the environment and whether the layer is intact. Damage from later building work, moisture and an unsuitable environment are the main reasons why the protection falls short locally.
What damages a coating?
- UV radiation and moisture for coatings applied outdoors
- Mechanical damage from impacts, collisions, or work carried out near the structure
- Chemical exposure in industrial environments
- Ageing of the material, especially if the environment does not suit the system
Signs that inspection is needed
- Visible cracks, flaking, or delamination of the coating
- Rust becoming visible through the coating
- Mechanical damage following renovation or use of the space
- New brackets, fixings or drill holes in the profile, made by other parties
How an inspection with thickness measurement works
- Requesting the data: which system was applied, with what thickness per profile, and what is in the completion file.
- Visual check of all protected profiles, with extra attention to connections, edges and places where work was done later.
- Thickness measurement with a magnetic or electromagnetic gauge. The instrument measures the total build-up; the thickness of primer and top coat is deducted from it.
- Comparison with the thickness schedule: the measured dry film thickness per profile must meet the calculated value, within the system's tolerances.
- Check of the rest of the system: does the system suit the environment, are the primer and topcoat compatible, and does the layer adhere properly. A sufficient film thickness alone does not prove that the protection is in order.
- Recording the result per profile, with photo and location, in the logbook.
A visual inspection is not always enough to assess the remaining fire resistance. If in doubt, we measure the film thickness and compare it with the film thickness schedule and the assessment of the system applied.
Repairing damage: how to do it right
A damaged coating can usually be repaired locally. The condition is that the repair stays within the original system:
- Use the same product, or a product that the manufacturer explicitly specifies as suitable, and follow the manufacturer's repair instructions.
- Remove loose parts, clean the substrate and restore the corrosion protection first.
- Apply the fire-resistant layer to the calculated thickness, overlapping onto the intact layer around it.
- Finish with the prescribed top coat and measure the thickness again.
- Record the repair: location, product, measured thickness and date.
Painting over it with ordinary paint seems harmless, but it can hinder the intumescence in a fire. So always consult before a fire-protected profile is given a different colour.
Documentation is just as important as the maintenance itself
For insurers and regulators, demonstrating periodic maintenance is often just as important as the quality of the maintenance itself. We record every inspection and repair action in a clear logbook.
Still deciding between coating and board cladding? Then read fire-resistant coating or cladding.
Frequently asked questions
There is no fixed period. A periodic visual check is sensible, for example annually in buildings where a lot of building work takes place or where the structure is vulnerable, and always after work near the structure. A film thickness measurement is needed if there is doubt about the film thickness, after damage and at handover.
Only with a top coat that the manufacturer has approved for that system. Ordinary paint can hinder the intumescence in a fire, reducing the protection.
With a magnetic or electromagnetic coating thickness gauge on the steel. The gauge gives the total build-up. After deducting primer and top coat, the dry film thickness of the fire-resistant layer remains, which is compared per profile with the calculated value.
Only if the system has been assessed for outdoor use and is finished with the prescribed top coat. Systems for indoor use age quickly outdoors due to rain, moisture and UV radiation.
Want to know more about maintenance & inspection?
Periodic maintenance and inspection of your fire protection, with everything verifiably recorded in a digital logbook.
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